[AIX] Implement AIX special alignment rule about double/long double

[Xiangling_L]

Summary

Implement AIX default power alignment rule by adding PreferredAlignment and PreferredNVAlignment in ASTRecordLayout class.

The implementation aims at returning correct value for __alignof(x) and alignof(x) under power alignment rules.

The AIX power alignment rules apply the natural alignment of the
"first member" if it is of a floating-point data type (or is an aggregate
whose recursively "first" member or element is such a type). The alignment
associated with these types for subsequent members use an alignment value
where the floating-point data type is considered to have 4-byte alignment.

For the purposes of the foregoing: vtable pointers, non-empty base classes,
and zero-width bit-fields count as prior members; members of empty class
types marked no_unique_address are not considered to be prior members.

Notes:

1. ASTRecordLayout Layout.Alignment records the min alignment/ABI align of object, which is also the value _Alignof(x) should return;

2.Layout.NonVirtualAlignment records min alignment of nv part of object

3. The size/nvsize of object will be rounded up to PreferredAlignment/PreferredNVAlignment on AIX.

4.getPreferredTypeAlign = __alignof(x) = preferred alignment of object

[Xiangling_L]

clang/lib/AST/ASTContext.cpp

2418

Thank you for your suggestion. I think currently, there are three targets disabling this query, XCore, X86 and MSP430. Since @efriedma mentioned we tried to avoid OS-specific checks here, I am not sure if mark this completely-target-specific is a good idea? Personally, I think a query like allowsLargerPreferedTypeAlignment() would give more semantic meaning.

[efriedma]

clang/lib/AST/RecordLayoutBuilder.cpp

661

Please explain here what the different values (-1, 0, 1, 2) mean. Or use an enum.

[Xiangling_L]

Replace int with an more self-explanatory enum;

[efriedma]

clang/lib/AST/RecordLayoutBuilder.cpp

667

Instead of specifically tracking whether you've found an OverlappingEmpty field, could you just have something like "bool FoundNonOverlappingEmptyField = false;", and set it to true when you handle a field that isn't OverlappingEmpty? I don't think we need to specifically track whether we've found an OverlappingEmpty field.

[Xiangling_L]

Simplify the code;
Add one more testcase related to [[no_unique_addr]];

clang/lib/AST/RecordLayoutBuilder.cpp

667

I think you are right. We do not need to specifically track whether we've found an OverlappingEmpty field. But I think we do need an enum to track if the first non-OverlappingEmptyField is handled or not.

Or the following case is problematic:

struct A {
  int : 0;
  double d;
};

The double d will mistakenly match FieldOffset == CharUnits::Zero() && D->getFieldIndex() != 0 && !IsOverlappingEmptyField && FoundNonOverlappingEmptyField , which we shouldn't because it is not the first member of the struct.

[efriedma]

clang/lib/AST/RecordLayoutBuilder.cpp

667

Okay, so now there are three states. But the FirstNonOverlappingEmptyFieldFound is transient: on exit from ItaniumRecordLayoutBuilder::LayoutField, FirstNonOverlappingEmptyFieldStatus never contains FirstNonOverlappingEmptyFieldFound. I think it would be more clear to use a local variable for that.

1922

I don't think you need to distinguish the D->getFieldIndex() == 0 case from the D->getFieldIndex() != 0 case.

[Xiangling_L]

Replace the transient status by a local var;
Clean up the code;

[efriedma]

LGTM

[jasonliu]

clang/include/clang/AST/RecordLayout.h

75

nit for comment: I don't think it's related to performance nowadays, and it's more for ABI-compat reason.

clang/lib/AST/ASTContext.cpp

2410

static_cast instead of c cast?

clang/lib/AST/RecordLayoutBuilder.cpp

827

We added supportsAIXPowerAlignment, so let's make use of that.
We could replace every call to isAIXLayout with supportsAIXPowerAlignment. This name is more expressive as well.

1233

Use a lambda for this query would be more preferable if same logic get used twice.

1922

Maybe it's a naive thought, but is it possible to replace NonOverlappingEmptyFieldFound with IsOverlappingEmptyField && FieldOffsets.size() == 0?

1996

hmm... Are we sure we should use FieldAlign instead of PreferredAlign here?
Same for the else below.

clang/lib/Basic/Targets/PPC.h

389

nit: use "else if" with the above if statement?
If it enters one of the Triples above, it's not necessary to check if it is AIX any more.

420–421

This could get combined with the new if for AIX below.

431

nit: use "else if" with the above if statement?

clang/test/Layout/aix-no-unique-address-with-double.cpp

63

Not an action item, but just an interesting note that, in some cases(like this one) power alignment rule could reverse the benefit of having [[no_unique_address]] at the first place.

[hubert.reinterpretcast]

clang/include/clang/Basic/TargetInfo.h

1400

Minor nit: Use backquotes around the XL option value "power".

clang/lib/AST/ASTContext.cpp

2421–2423

Comment should be updated.

2432

Does supportsAIXPowerAlignment express the condition we want to check here? That might be true for an implementation operating with mac68k alignment rules.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

661

I suggest to replace (if correct) "non-overlappingEmptyField" with "non-empty or empty-but-non-overlapping field".

663

Having "handled" at the front is a better indication (aside from the type) that "field" is not the main term. Also, minor nit: there's trailing whitespace at the end of the line here.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1928

I tried clang -cc1 -triple powerpc-ibm-aix -fsyntax-only with
<stdin>:

struct A {
  struct B {
    double d[3];
  } b;
};

extern char x[__alignof__(struct A)];
extern char x[8];

I got an assertion failure:

clang: /src/clang/lib/AST/RecordLayoutBuilder.cpp:2078: void {anonymous}::ItaniumRecordLayoutBuilder::UpdateAlignment(clang::CharUnits, clang::CharUnits, clang::CharUnits): Assertion `llvm::isPowerOf2_64(PreferredNewAlignment.getQuantity()) && "Alignment not a power of 2"' failed.

[hubert.reinterpretcast]

clang/test/Layout/aix-double-struct-member.cpp

2

There's no testing for _Complex types.

struct A {
  struct B {
    long double _Complex d[3];
  } b;
};

extern char x[__alignof__(struct A)];
extern char x[8];

[Xiangling_L]

Addressed comments;
Fixed the ICE problem with array as first member;
Add support for Complex type;

clang/lib/AST/ASTContext.cpp

2432

Yeah, supportsAIXPowerAlignment cannot separate the preferred alignment of double, long double between power/natural and mac68k alignment rules. But I noticed that currently, AIX target on wyvern or XL don't support mac68k , so maybe we should leave further changes to the patch which is gonna implement mac68k alignment rules? The possible solution I am thinking is we can add checking if the decl has AlignMac68kAttr into query to separate things out.

Another thing is that once we start supporting mac68k alignment rule(if we will), should we also change the ABI align values as well? (e.g. for double, it should be 2 instead)

clang/lib/AST/RecordLayoutBuilder.cpp

661

Thanks for your suggestion. But I kinda prefer using NonOverlappingEmptyField, it is more consistent with IsOverlappingEmptyField. And also the equivalent name to NonOverlappingEmptyField is NonOverlappingAndNonEmptyField which is tedious I think.

1922

I don't think these two work the same. NonOverlappingEmptyFieldFound represents the 1st non-empty and non-overlapping field in the record. IsOverlappingEmptyField && FieldOffsets.size() == 0 represents something opposite.

1996

The way I see the PreferredAlign is not the real alignment the record uses (which I believe the community don't expect us to see it that way either). All code here should be attached to ABI align. Specially, on AIX, PreferredAlign is something we use to round up the record size, but it won't affect the record layout besides of that. So in other words, we are just tracking what PreferredAlignment value is here.

[hubert.reinterpretcast]

clang/lib/AST/ASTContext.cpp

2432

If the "base state" is AIX power alignment for a platform, I suggest that the name be defaultsToAIXPowerAlignment.

clang/lib/AST/RecordLayoutBuilder.cpp

661

I am suggesting a change to the comment and not the name here. If both the comment and the name uses the same (possibly confusing) form to express the concept, then the comment does not aid comprehension of the code.

[Xiangling_L]

Adjust the function name;
Adjust the comment;

[jasonliu]

clang/lib/AST/RecordLayoutBuilder.cpp

1922

You are right. I meant could we replace it with !(IsOverlappingEmptyField && FieldOffsets.size() == 0)?

[Xiangling_L]

clang/lib/AST/RecordLayoutBuilder.cpp

1922

I don't think so. The replacement does not work for the case:

struct A {
  int : 0;
  double d;
};

where __alignof(A) should be 4;

[jasonliu]

clang/lib/AST/RecordLayoutBuilder.cpp

1922

Got it. Thanks!

[jasonliu]

LGTM. I have no further comments on this patch.

[hubert.reinterpretcast]

clang/include/clang/AST/RecordLayout.h

75

I'm still evaluating this; however, I might as well note a minor nit first:
s/perserving/preserving/g;
for all instances within this patch.

[Xiangling_L]

Corrected the comments;

[hubert.reinterpretcast]

clang/test/Layout/aix-double-struct-member.cpp

2

I am concerned that none of the tests actually create an instance of the classes under test and check the alignment (or related adjustments) in the IR. That is, we set up the preferred alignment value but don't check that we use it where we should.

As it is, it seems array new/delete has problems:

#include <assert.h>
extern "C" void *calloc(decltype(sizeof 0), decltype(sizeof 0));
extern "C" void free(void *);
extern "C" int printf(const char *, ...);

extern void *allocated_ptr;
extern decltype(sizeof 0) allocated_size;
struct B {
  double d;
  ~B() {}
  static void *operator new[](decltype(sizeof 0) sz);
  static void operator delete[](void *p, decltype(sizeof 0) sz);
};
B *allocBp();

#ifdef ALLOCBP
void *allocated_ptr;
decltype(sizeof 0) allocated_size;
void *B::operator new[](decltype(sizeof 0) sz) {
  void *alloc = calloc(1u, allocated_size = sz);
  printf("%p: %s\n", alloc, __PRETTY_FUNCTION__);
  printf("%zu\n", sz);
  return allocated_ptr = alloc;
}
void B::operator delete[](void *p, decltype(sizeof 0) sz) {
  printf("%p: %s\n", p, __PRETTY_FUNCTION__);
  printf("%zu\n", sz);
  assert(sz == allocated_size);
  assert(p == allocated_ptr);
  free(p);
}
B *allocBp() { return new B[2]; }
#endif

#ifdef MAIN
int main(void) { delete[] allocBp(); }
#endif

The xlclang++ invocation from XL C/C++ generates padding before the 32-bit new[] cookie. I'm not seeing that padding with this patch.

[hubert.reinterpretcast]

clang/test/Layout/aix-double-struct-member.cpp

3

My build with this patch also hits cases where the preferred alignment is increased to 8, but the offset of the associated member is not 8-byte aligned:

extern "C" int printf(const char *, ...);
struct A0 {};
struct Y : A0 {
  double mem;
};
struct Z : A0 {
  Y y;
};
extern char alignz[__alignof__(Z)];
extern char alignz[8];
int main(void) {
  Z z;
  printf("%td\n",
         &reinterpret_cast<char &>(z.y) - &reinterpret_cast<char &>(z));
}

*** Dumping AST Record Layout
         0 | struct Z
         0 |   struct A0 (base) (empty)
         4 |   struct Y y
         4 |     struct A0 (base) (empty)
         4 |     double mem
           | [sizeof=16, dsize=12, align=4, preferredalign=8,
           |  nvsize=12, nvalign=4, preferrednvalign=8]

238

Typo: s/tes8/test8/;

348

Same comment.

[hubert.reinterpretcast]

clang/lib/AST/ASTContext.cpp

2421–2423

I suggest to clarify the binding of the parenthetical and also to make the context that the required alignment is lower than the natural alignment more explicit:

// Double (and, for targets supporting AIX `power` alignment, long double) and
// long long should be naturally aligned (despite requiring less alignment) if
// possible.

clang/lib/AST/RecordLayoutBuilder.cpp

1216–1217

This comment belongs inside the lambda.

1217

The lambda is currently being named for what is produced based on the identity of what gets passed to it and not named for what it does.

This should be named getPackedBaseAlignFromUnpacked or similar.

1219

I suggest not applying "ABI compat" with Clang <= 6 on AIX. There was is no Clang <= 6 with AIX support.

1269

Suggestion:

// AIX `power` alignment does not apply the preferred alignment for non-union
// classes if the source of the alignment (the current base in this context)
// follows introduction of the first member with allocated space.

1801

The name is wrong for the value (the value corresponding to this name is !IsOverlappingEmptyField). I would suggest something like FoundNonOverlappingEmptyFieldToHandle.

1804

Move the definition of the variable here and just use the if condition as the initializer.

[Xiangling_L]

clang/test/Layout/aix-double-struct-member.cpp

2

Thank. I will create more practical testcases as you mentioned in your concern. And regarding to padding before the 32-bit new[] cookie issue, I am wondering is that part of power alignment rule or what rules do we follow to generate this kind of padding?

[hubert.reinterpretcast]

clang/test/Layout/aix-double-struct-member.cpp

2

The padding has to do with the alignment. The allocation function returns 8-byte aligned memory. The 32-bit cookie takes 4 of the first 8 bytes. The type's preferred alignment is 8, so there are 4 bytes of padding.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1269

Adjustment to my suggestion:
s/first member with allocated space/first subobject with exclusively allocated space/;

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1915

Suggestion:

// The AIX `power` alignment rules apply the natural alignment of the
// "first member" if it is of a floating-point data type (or is an aggregate
// whose recursively "first" member or element is such a type). The alignment
// associated with these types for subsequent members use an alignment value
// where the floating-point data type is considered to have 4-byte alignment.
//
// For the purposes of the foregoing: vtable pointers, non-empty base classes,
// and zero-width bit-fields count as prior members; members of empty class
// types marked `no_unique_address` are not considered to be prior members.

This fixes a number of issues with the comment, including:

• The meaning of "first member" is unclear and the intended meaning is unlikely to be understood from common meanings of the term.
• The recursive application of the rule was not captured (the relationship is not merely "contains").
• The statement about 4-byte alignment needed to take stricter alignment due to other factors into account.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1825

See my other comment for rationale on why HandledFirstNonOverlappingEmptyField should be set to !IsUnion instead of true.

A comment would be appropriate here:

if (FoundNonOverlappingEmptyField) {
  // For a union, the current field does not represent all "firsts".
  HandledFirstNonOverlappingEmptyField = !IsUnion;
}

1923

IsOverlappingEmptyField is still in play (as seen in further checks below). I do not believe it is appropriate to set HandledFirstNonOverlappingEmptyField to true in that case (possible because IsUnion overrides what is currently called FoundNonOverlappingEmptyField).

There are a few ways to address this. For example, HandledFirstNonOverlappingEmptyField could be set to !IsUnion instead for to true. This is semantically sound, because HandledFirstNonOverlappingEmptyField is meant to indicate that there would not be further "firsts" to consider (and that is not true for unions).

I believe the code should not require user to convince themselves that non-sequitur logic washes away, so I would like a fix for this although it introduces no functional change.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1928

I don't think there's a reason to use getBaseElementType (which is used to handle arrays) on the element type of a ComplexType.

1929

I believe castAs should be expected to succeed here.

1932

I believe an assertion that PreferredAlign was 4 would be appropriate.

1937

Use a lambda instead of duplicating the code.

1942

Is there a reason to use getBaseElementTypeUnsafe for this case and Context.getBaseElementType for the other ones? Also, it would make sense to factor out the array-type considerations once at the top of the if-else chain instead of doing so in each alternative.

1944

I'd be a bit concerned if this failed. Can we assert that we get a non-null pointer back?

[Xiangling_L]

clang/test/Layout/aix-double-struct-member.cpp

2

Regarding with checking the alignment where we use them, AFAIK the problematic cases include not only the cookie padding issue you mentioned here, but also the alignment of argument type, return type etc.

So I am wondering does it make sense to have them handled in a separate patch since this is already a big one? We can use this patch to implement the correct value of __alignof and alignof and use a second patch to handle the places where we use them where we should?

[hubert.reinterpretcast]

clang/test/Layout/aix-double-struct-member.cpp

2

Yes, we can scope the patch that way somewhat; however, some cases of "[using the __alignof__ value] where we should" that is missing is within the determination of the base and field offsets. We should keep those within the scope of this patch.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1921

This if condition does not currently capture that a zero-extent array in a base class renders the base class not empty.

struct Z { char zea[0]; };
struct A {
  Z z [[no_unique_address]];
  double d;
};
struct B : Z { double d; };
static_assert(__alignof__(A) == __alignof__(B));

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1269

Add:
[ ... ] or zero-extent array.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1950

Testing using my build with this patch seems to indicate that tracking FieldAlign for UnpackedFieldAlign does not lead to the desired result.

The QQ and ZZ cases differ only on the packed attribute on Q. They are observed to have different sizes; however, we get a -Wpacked diagnostic claiming that the packed attribute was unnecessary (and could therefore be removed).

struct [[gnu::packed]] Q {
  double x [[gnu::aligned(4)]];
};
struct QQ : Q { char x; };

struct Z {
  double x [[gnu::aligned(4)]];
};
struct ZZ : Z { char x; };

extern char qx[sizeof(QQ)];
extern char qx[12];
extern char qz[sizeof(ZZ)];
extern char qz[16];

<stdin>:1:24: warning: packed attribute is unnecessary for 'Q' [-Wpacked]
struct [[gnu::packed]] Q {
                       ^
1 warning generated.

[hubert.reinterpretcast]

clang/lib/AST/ASTContext.cpp

2432

This last question about the ABI align values is relevant to considerations for natural alignment support as well. More generally, the question is whether the "minimum alignment" of the type in a context subject to alternative alignment rules is altered to match said alignment rule. This is observable via the diagnostic associated with C++11 alignment specifiers.

The existing behaviour of mac68k alignment suggests that the "minimum alignment" is context-free.

#pragma options align=mac68k
struct Q {
  double x alignas(2);  // expected-error {{less than minimum alignment}}
};
#pragma options align=reset

Compiler Explorer link: https://godbolt.org/z/9NM5_-

[Xiangling_L]

clang/lib/AST/ASTContext.cpp

2432

Thank you for your explanation.

clang/lib/AST/RecordLayoutBuilder.cpp

1929

castAs is not declared in current context, do we really want to use it by introducing one more header?

1942

Sorry, I didn't pay attention to the different versions of getBaseElementType functions here and I believe this part of code came from our old compiler's changesets. My understanding would be since type qualifiers are not very meaningful in our case and getBaseElementTypeUnsafe() is more efficient than getBaseElementType(), we can use getBaseElementTypeUnsafe() all over the place instead.

[Xiangling_L]

Rebased on the latest master;
Fixed -Wpacked warning issue;
Fixed EmptySubobjects related offset issue;
Fixed zero-extent array in a base class related issue;
Addressed other comments;

[hubert.reinterpretcast]

clang/lib/AST/ASTContext.cpp

2409

Please add a comment regarding the situations where the ABIAlign value is greater than the PreferredAlignment value. It may be appropriate to assert that, absent those cases, the PreferredAlignment value is at least that of ABIAlign.

2409

It does not appear that the maximum of the two values is the correct answer:

struct C {
  double x;
} c;
typedef struct C __attribute__((__aligned__(2))) CC;

CC cc;
extern char x[__alignof__(cc)];
extern char x[2]; // this is okay with IBM XL C/C++

clang/lib/AST/RecordLayoutBuilder.cpp

1932

It seems that overriding the value should only be done after additional checks:

typedef double __attribute__((__aligned__(2))) Dbl;
struct A {
  Dbl x;
} a;
extern char x[__alignof__(a)];
extern char x[2]; // this is okay with IBM XL C/C++

I am getting concerned that the logic here overlaps quite a bit with getPreferredTypeAlign and refactoring to make the code here more common with getPreferredTypeAlign is necessary.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1929

castAs should be declared:
https://clang.llvm.org/doxygen/classclang_1_1Type.html#a436b8b08ae7f2404b4712d37986194ce

Also, the additional point is that the if here should be unnecessary. BTy should not be null. We should use castAs to gain the guarantee (with assertions) that BTy is not null.

[Xiangling_L]

Fixed the typedef related issues;
Added more testcases;

clang/lib/AST/ASTContext.cpp

2409

Please add a comment regarding the situations where the ABIAlign value is greater than the PreferredAlignment value.

I added a if condition to guard the situation where ABIAlign should be returned instead of adding a comment. Please let me know if that is sufficient.

clang/lib/AST/RecordLayoutBuilder.cpp

1932

Fixed the typedef related cases with my new changes, and the overlaps were not a lot as I expected. So I didn't do any refactoring yet. Please let me know if you still think it's necessary to refactor the code somehow.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

666

Minor nit: s/as base/as a base/;

703

Minor nit: Please fix the formatting.

1223

Thanks; verified that this is correct with xlclang++ from IBM XL C/C++ for AIX with:

struct A {
  char x;
};
struct B {
  int x;
};
struct __attribute__((__packed__)) C : A, B {} c;

Length is 5:

[10]    m   0x00000004      .bss     1  extern                    c
[11]    a4  0x00000005       0    0     CM       RW    0    0

@Xiangling_L, I suggest adding a case for this to the tests.

1273

Unions cannot have base classes. Please assert !IsUnion.

1277

Suggestion:

// The maximum field alignment overrides the base align/(AIX-only) preferred
// base align.

clang/test/Layout/aix-power-alignment-typedef.cpp

19

Instead of checking the value of a, the alignment can be checked more directly from the IR for cc.

[hubert.reinterpretcast]

clang/lib/AST/ASTContext.cpp

2414

Minor nit: s/is/should be/;

clang/lib/AST/RecordLayoutBuilder.cpp

1208

Just set HandledFirstNonOverlappingEmptyField to true with a comment before the if:
By handling a base class that is not empty, we're handling the "first (inherited) member".

1824

Add a comment before the if:

// We're going to handle the "first member" based on
// `FoundNonOverlappingEmptyFieldToHandle` during the current invocation of
// this function; record it as handled for future invocations.

Given the rationale from the comment, move the subject if to immediately after the determination of FoundNonOverlappingEmptyFieldToHandle. That way, the setting of HandledFirstNonOverlappingEmptyField becomes less complicated to track.

1855

It seems that the code to set AlignIsRequired is missing from this path.

typedef double Dbl __attribute__((__aligned__(2)));
typedef Dbl DblArr[];

union U {
  DblArr fam;
  char x;
};

U u[2];
extern char x[sizeof(u)];
extern char x[4];

1928

I think the if condition above is too complicated as a filter for setting HandledFirstNonOverlappingEmptyField. I would prefer if we don't need to set HandledFirstNonOverlappingEmptyField here. Please see my other comment about HandledFirstNonOverlappingEmptyField.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1930

"Qualified" is a term of art in the context of C/C++ types. Please remove "IfQualified" from the name. The lambda just needs to be named for what it does. When naming it for the conditions where it should be called, "if" (as opposed to "assuming") implies that the function checks the condition itself.

1947

Please don't write a check on a variable right after making an assertion on what its value should be.

[Xiangling_L]

Fixed typedef issue on incomplete array field and add a test for it;
Added a test for where pack attribute on object also apply on base classes;
Addressed other comments;

clang/lib/AST/RecordLayoutBuilder.cpp

1223

Sure, I will add it.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1068

I would suggest setting HandledFirstNonOverlappingEmptyField to true here with an assertion that the current type is not a union.

1807

The condition is still more complex than I think it should be.

If we have found a "first" other-than-overlapping-empty-field, then we should set HandledFirstNonOverlappingEmptyField to true for non-union cases.

If HandledFirstNonOverlappingEmptyField being false is not enough for FieldOffset == CharUnits::Zero() to be true, then I think the correction would be to set HandledFirstNonOverlappingEmptyField in more places.

I would like to remove the check on FieldOffset == CharUnits::Zero() from here and instead have an assertion that !HandledFirstNonOverlappingEmptyField implies FieldOffset == CharUnits::Zero().

Also, since we're managing HandledFirstNonOverlappingEmptyField in non-AIX cases, we should remove the DefaultsToAIXPowerAlignment condition for what is currently named FoundFirstNonOverlappingEmptyFieldToHandle (adjusting uses of it as necessary) and rename FoundFirstNonOverlappingEmptyFieldToHandle to FoundFirstNonOverlappingEmptyField.

1854–1855

ATy seems to be an unused variable now.

1856

I guess this works (we have a test for it), but the previous code made a point to use the element type and not the array type (and the comment above says we can't directly query getTypeInfo with the array type). @Xiangling_L, can you confirm if the comment is out-of-date and update it?

1926

It should now be the case that FoundFirstNonOverlappingEmptyFieldToHandle is true for all union members that are not empty, meaning that the IsUnion part of the check only serves to admit attempts to handle types that are empty (and thus does not have subobjects that would induce an alignment upgrade).

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1274

This needs to check HandledFirstNonOverlappingEmptyField:

struct A {
  char x[0];
};
struct B {
  double d;
};
struct C : A, B { char x; } c;

1275

Note that PreferredBaseAlign is only truly meaningful after this line, and related fields, such as UnpackedPreferredBaseAlign, require similar treatment. With UnpackedAlignTo being dependent on a meaningful value of UnpackedPreferredBaseAlign, it needs an update here as well.

Consider the following source. Noting that C and D are identical except for the packed attribute and yield identical layout properties despite that difference, we should be getting a -Wpacked warning with -Wpacked (but it is missing).

struct A {
  double d;
};

struct B {
  char x[8];
};

struct [[gnu::packed]] C : B, A { // expected-warning {{packed attribute is unnecessary}}
  char x alignas(4)[8];
} c;

struct D : B, A {
  char x alignas(4)[8];
} d;

*** Dumping AST Record Layout
         0 | struct C
         0 |   struct B (base)
         0 |     char [8] x
         8 |   struct A (base)
         8 |     double d
        16 |   char [8] x
           | [sizeof=24, dsize=24, align=4, preferredalign=4,
           |  nvsize=24, nvalign=4, preferrednvalign=4]

*** Dumping AST Record Layout
         0 | struct D
         0 |   struct B (base)
         0 |     char [8] x
         8 |   struct A (base)
         8 |     double d
        16 |   char [8] x
           | [sizeof=24, dsize=24, align=4, preferredalign=4,
           |  nvsize=24, nvalign=4, preferrednvalign=4]

[Xiangling_L]

clang/lib/AST/RecordLayoutBuilder.cpp

1807

Also, since we're managing HandledFirstNonOverlappingEmptyField in non-AIX cases, we should remove the DefaultsToAIXPowerAlignment condition for what is currently named FoundFirstNonOverlappingEmptyFieldToHandle

I am not sure if we want to remove the DefaultsToAIXPowerAlignment condition and bother with maintaining correct status of HandledFirstNonOverlappingEmptyField for other targets.

We are actually claiming HandledFirstNonOverlappingEmptyField is an auxiliary flag used for AIX only in its definition comments.

Besides, if we do want to manage HandledFirstNonOverlappingEmptyField in non-AIX cases, I noticed that we have to set this flag to true somewhere for objective-C++ cases.

1856

I am sure getTypeInfo can recognize the element type for IncompleteArray. I will update the comments.

[Xiangling_L]

Fixed a -Wpacked related case and added the case to the tests;
Fixed the base class related code issue;
Addressed other comments;

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1807

Okay, the other option I'm open is setting HandledFirstNonOverlappingEmptyField to true up front when not dealing with AIX power alignment.

[Xiangling_L]

clang/lib/AST/RecordLayoutBuilder.cpp

1807

Thanks, that works too. I will address it in the next commit.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1269–1270

It seems this is a leftover copy of the code that has been moved above?

1806

The rename I suggested in my previous round of review was in coordination with maintaining the value not just for AIX. Since we're only maintaining the value for AIX, I prefer the previous name (or FoundFirstNonOverlappingEmptyFieldForAIX).

1807

Please merge the if conditions to reduce nesting:

if (DefaultsToAIXPowerAlignment && !HandledFirstNonOverlappingEmptyField) {

1814

Keep this reference to the variable up-to-date with its name.

1817

Change the condition of the if here to !IsOverlappingEmptyField and move the setting of FoundFirstNonOverlappingEmptyField to true into this if.

Move the previous comment and merge it with this one here:

[ ... ] record it as handled for future invocations (except for unions, because the current field does not represent all "firsts").

1927

Sorry for not seeing this earlier (I only notice some things when I hide the inline comments). I think performBuiltinTypeAlignmentUpgrade would read better at the call site (and better capture the checking, which is based on the kind of built-in type, that is within the lambda).

clang/test/Layout/aix-Wpacked.cpp

9 ↗

(On Diff #276528)

Clang diagnostics are normally checked using -verify (as opposed to FileCheck). To use it, I think this needs to be split into the "expecting no diagnostics" and the "expecting diagnostics" cases. As it is, I think the CHECK-NOT has a problem because it checks for plain 'Q'.

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1210

We need some sort of IsFirstNonEmptyBase to record that the current base qualifies for the alignment upgrade:

struct A { double x; };
struct B : A {} b;

1266

Query !IsFirstNonEmptyBase instead of HandledFirstNonOverlappingEmptyField here.

[Xiangling_L]

Fixed a base class related case by adding IsFirstNonEmpty flag;
Split the aix-Wpacked.cpp testcase into two;
Addressed other comments;

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1246

Move the comment to above the previous if and make the following if the else of the previous if.

1807

I'm not seeing the change for https://reviews.llvm.org/D79719?id=276143#inline-767942?

clang/test/Layout/aix-Wpacked-expecting-diagnostics.cpp

19

Minor nit: Remove the space before the semicolon.

clang/test/Layout/aix-Wpacked-no-diagnostics.cpp

15

Is there a reason to drop the FileCheck checking for the layout?

[Xiangling_L]

Set Handled... = true for non-AIX power alignment;
Addressed other comments;

[hubert.reinterpretcast]

clang/lib/AST/RecordLayoutBuilder.cpp

1244

IsFirstNonEmptyBase can be removed. It is set, but not used.

[Xiangling_L]

Removed unused var;

[Xiangling_L]

clang/test/Layout/aix-Wpacked-no-diagnostics.cpp

15

I dropped the FileCheck because the layout of QQ and Q are fairly simple and wanted the test focus more on no-diagnostics side. But I can add it back if that helps.

[hubert.reinterpretcast]

I've done another pass over the code (but did not get through the tests). I have no comments about the code at this time. My understanding is that @jasonliu will be doing another pass over this patch, so he can approve while I'm away on vacation.

[jasonliu]

clang/lib/AST/ASTContext.cpp

2418

Should this if statement go above the if (const auto *RT = T->getAs<RecordType>()) ?
When Target does not allow larger prefered type alignment, then we should return ABIAlign immediately without going through the RecordType query?

clang/lib/AST/RecordLayoutBuilder.cpp

1235

Add const?

1804

const ?

clang/lib/Basic/Targets/PPC.h

425

SuitableAlign is set in line 412 as well. Please consider combining the two if statements if grouping things together makes code easier to parse.

clang/test/Layout/aix-double-struct-member.cpp

3

You are not using < %s here. So -x c++ is redundant?

306

b is not necessary when you take the sizeof of B below?

clang/test/Layout/aix-no-unique-address-with-double.cpp

139

I think this case is interesting and may worth adding too:

struct F {
  [[no_unique_address]] Empty emp, emp2;
  double d;
};

clang/test/Layout/aix-power-alignment-typedef.cpp

13

remove c ?

26

remove a?

44

remove u?

[Xiangling_L]

clang/lib/AST/ASTContext.cpp

2418

Agree. I will update this.

clang/test/Layout/aix-double-struct-member.cpp

3

Yeah, thanks, I will remove it.

clang/test/Layout/aix-no-unique-address-with-double.cpp

139

Sure.

[Xiangling_L]

Add one more testcase;
Addressed other comments;

[jasonliu]

Thanks. No further comments from me.

[Xiangling_L]

• Simplified the test command line;
• Split the typedef related tests into two to address the LIT testcase failure on windows platform;

[ebevhan]

clang/lib/AST/RecordLayoutBuilder.cpp

1779

It seems that in factoring out this to setDeclInfo, it was changed from using getTypeInfoInChars to using getTypeInfo+toCharUnitsFromBits. This is causing some downstream issues for us with non-bytesize-multiple types.

Changing setDeclInfo to use the original function instead seems to work without issues. Would it be acceptable to change this?

[efriedma]

clang/lib/AST/RecordLayoutBuilder.cpp

1779

In general, we want to avoid representing type size/alignment in bits where it isn't necessary; refactoring along those lines is welcome.

[ebevhan]

I submitted a patch with the changes at D85191.

clang/include/clang/AST/RecordLayout.h

private:
   CharUnits Size;
 
   /// DataSize - Size of record in characters without tail padding.
   CharUnits DataSize;
 
   // Alignment - Alignment of record in characters.
   CharUnits Alignment;
 
+  // PreferredAlignment - Preferred alignment of record in characters. This
+  // can be different than Alignment in cases where it is beneficial for
+  // performance or backwards compatibility preserving (e.g. AIX-ABI).
+  CharUnits PreferredAlignment;
+
   // UnadjustedAlignment - Maximum of the alignments of the record members in
   // characters.
   CharUnits UnadjustedAlignment;
 
   /// RequiredAlignment - The required alignment of the object.  In the MS-ABI
   /// the __declspec(align()) trumps #pramga pack and must always be obeyed.
   CharUnits RequiredAlignment;
 
   /// FieldOffsets - Array of field offsets in bits.
   ASTVector<uint64_t> FieldOffsets;
 
   /// CXXRecordLayoutInfo - Contains C++ specific layout information.
   struct CXXRecordLayoutInfo {
     /// NonVirtualSize - The non-virtual size (in chars) of an object, which is
     /// the size of the object without virtual bases.
     CharUnits NonVirtualSize;
 
     /// NonVirtualAlignment - The non-virtual alignment (in chars) of an object,
     /// which is the alignment of the object without virtual bases.
     CharUnits NonVirtualAlignment;
 
+    /// PreferredNVAlignment - The preferred non-virtual alignment (in chars) of
+    /// an object, which is the preferred alignment of the object without
+    /// virtual bases.
+    CharUnits PreferredNVAlignment;
+
     /// SizeOfLargestEmptySubobject - The size of the largest empty subobject
     /// (either a base or a member). Will be zero if the class doesn't contain
     /// any empty subobjects.
     CharUnits SizeOfLargestEmptySubobject;
 
     /// VBPtrOffset - Virtual base table offset (Microsoft-only).
     CharUnits VBPtrOffset;
 
struct CXXRecordLayoutInfo {
     VBaseOffsetsMapTy VBaseOffsets;
   };
 
   /// CXXInfo - If the record layout is for a C++ record, this will have
   /// C++ specific information about the record.
   CXXRecordLayoutInfo *CXXInfo = nullptr;
 
   ASTRecordLayout(const ASTContext &Ctx, CharUnits size, CharUnits alignment,
-                  CharUnits unadjustedAlignment,
+                  CharUnits preferredAlignment, CharUnits unadjustedAlignment,
                   CharUnits requiredAlignment, CharUnits datasize,
                   ArrayRef<uint64_t> fieldoffsets);
 
   using BaseOffsetsMapTy = CXXRecordLayoutInfo::BaseOffsetsMapTy;
 
   // Constructor for C++ records.
-  ASTRecordLayout(const ASTContext &Ctx,
-                  CharUnits size, CharUnits alignment,
-                  CharUnits unadjustedAlignment,
-                  CharUnits requiredAlignment,
-                  bool hasOwnVFPtr, bool hasExtendableVFPtr,
-                  CharUnits vbptroffset,
-                  CharUnits datasize,
-                  ArrayRef<uint64_t> fieldoffsets,
+  ASTRecordLayout(const ASTContext &Ctx, CharUnits size, CharUnits alignment,
+                  CharUnits preferredAlignment, CharUnits unadjustedAlignment,
+                  CharUnits requiredAlignment, bool hasOwnVFPtr,
+                  bool hasExtendableVFPtr, CharUnits vbptroffset,
+                  CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
                   CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
+                  CharUnits preferrednvalignment,
                   CharUnits SizeOfLargestEmptySubobject,
-                  const CXXRecordDecl *PrimaryBase,
-                  bool IsPrimaryBaseVirtual,
+                  const CXXRecordDecl *PrimaryBase, bool IsPrimaryBaseVirtual,
                   const CXXRecordDecl *BaseSharingVBPtr,
-                  bool EndsWithZeroSizedObject,
-                  bool LeadsWithZeroSizedBase,
-                  const BaseOffsetsMapTy& BaseOffsets,
-                  const VBaseOffsetsMapTy& VBaseOffsets);
+                  bool EndsWithZeroSizedObject, bool LeadsWithZeroSizedBase,
+                  const BaseOffsetsMapTy &BaseOffsets,
+                  const VBaseOffsetsMapTy &VBaseOffsets);
 
   ~ASTRecordLayout() = default;
 
   void Destroy(ASTContext &Ctx);
 
 public:
   ASTRecordLayout(const ASTRecordLayout &) = delete;
   ASTRecordLayout &operator=(const ASTRecordLayout &) = delete;
 
   /// getAlignment - Get the record alignment in characters.
   CharUnits getAlignment() const { return Alignment; }
 
+  /// getPreferredFieldAlignment - Get the record preferred alignment in
+  /// characters.
+  CharUnits getPreferredAlignment() const { return PreferredAlignment; }
+
   /// getUnadjustedAlignment - Get the record alignment in characters, before
   /// alignment adjustement.
   CharUnits getUnadjustedAlignment() const { return UnadjustedAlignment; }
 
   /// getSize - Get the record size in characters.
   CharUnits getSize() const { return Size; }
 
   /// getFieldCount - Get the number of fields in the layout.
   unsigned getFieldCount() const { return FieldOffsets.size(); }
 
   /// getFieldOffset - Get the offset of the given field index, in
   /// bits.
   uint64_t getFieldOffset(unsigned FieldNo) const {
     return FieldOffsets[FieldNo];
   }
 
   /// getDataSize() - Get the record data size, which is the record size
   /// without tail padding, in characters.
-  CharUnits getDataSize() const {
-    return DataSize;
-  }
+  CharUnits getDataSize() const { return DataSize; }
 
   /// getNonVirtualSize - Get the non-virtual size (in chars) of an object,
   /// which is the size of the object without virtual bases.
   CharUnits getNonVirtualSize() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
 
     return CXXInfo->NonVirtualSize;
   }
 
-  /// getNonVirtualSize - Get the non-virtual alignment (in chars) of an object,
-  /// which is the alignment of the object without virtual bases.
+  /// getNonVirtualAlignment - Get the non-virtual alignment (in chars) of an
+  /// object, which is the alignment of the object without virtual bases.
   CharUnits getNonVirtualAlignment() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
 
     return CXXInfo->NonVirtualAlignment;
   }
 
+  /// getPreferredNVAlignment - Get the preferred non-virtual alignment (in
+  /// chars) of an object, which is the preferred alignment of the object
+  /// without virtual bases.
+  CharUnits getPreferredNVAlignment() const {
+    assert(CXXInfo && "Record layout does not have C++ specific info!");
+
+    return CXXInfo->PreferredNVAlignment;
+  }
+
   /// getPrimaryBase - Get the primary base for this record.
   const CXXRecordDecl *getPrimaryBase() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
 
     return CXXInfo->PrimaryBase.getPointer();
   }
 
   /// isPrimaryBaseVirtual - Get whether the primary base for this record
public:
   }
 
   /// hasVBPtr - Does this class have a virtual function table pointer.
   bool hasVBPtr() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
     return !CXXInfo->VBPtrOffset.isNegative();
   }
 
-  CharUnits getRequiredAlignment() const {
-    return RequiredAlignment;
-  }
+  CharUnits getRequiredAlignment() const { return RequiredAlignment; }
 
   bool endsWithZeroSizedObject() const {
     return CXXInfo && CXXInfo->EndsWithZeroSizedObject;
   }
 
   bool leadsWithZeroSizedBase() const {
     assert(CXXInfo && "Record layout does not have C++ specific info!");
     return CXXInfo->LeadsWithZeroSizedBase;

clang/include/clang/Basic/TargetInfo.h

 
   /// Check if the target supports CFProtection branch.
   virtual bool
   checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const;
 
   /// Whether target allows to overalign ABI-specified preferred alignment
   virtual bool allowsLargerPreferedTypeAlignment() const { return true; }
 
+  /// Whether target defaults to the `power` alignment rules of AIX.
+  virtual bool defaultsToAIXPowerAlignment() const { return false; }
+
   /// Set supported OpenCL extensions and optional core features.
   virtual void setSupportedOpenCLOpts() {}
 
   /// Set supported OpenCL extensions as written on command line
   virtual void setOpenCLExtensionOpts() {
     for (const auto &Ext : getTargetOpts().OpenCLExtensionsAsWritten) {
       getTargetOpts().SupportedOpenCLOptions.support(Ext);
     }

clang/lib/AST/ASTContext.cpp

CharUnits ASTContext::getTypeUnadjustedAlignInChars(QualType T) const {
   return toCharUnitsFromBits(getTypeUnadjustedAlign(T));
 }
 CharUnits ASTContext::getTypeUnadjustedAlignInChars(const Type *T) const {
   return toCharUnitsFromBits(getTypeUnadjustedAlign(T));
 }
 
 /// getPreferredTypeAlign - Return the "preferred" alignment of the specified
 /// type for the current target in bits.  This can be different than the ABI
-/// alignment in cases where it is beneficial for performance to overalign
-/// a data type.
+/// alignment in cases where it is beneficial for performance or backwards
+/// compatibility preserving to overalign a data type.
 unsigned ASTContext::getPreferredTypeAlign(const Type *T) const {
   TypeInfo TI = getTypeInfo(T);
   unsigned ABIAlign = TI.Align;
 
   T = T->getBaseElementTypeUnsafe();
 
   // The preferred alignment of member pointers is that of a pointer.
   if (T->isMemberPointerType())
     return getPreferredTypeAlign(getPointerDiffType().getTypePtr());
 
+  if (const auto *RT = T->getAs<RecordType>()) {
+    if (TI.AlignIsRequired)
+      return ABIAlign;
+
+    unsigned PreferredAlign = static_cast<unsigned>(
+        toBits(getASTRecordLayout(RT->getDecl()).PreferredAlignment));
+    assert(PreferredAlign >= ABIAlign &&
+           "PreferredAlign should be at least as large as ABIAlign.");
+    return PreferredAlign;
+  }
+
   if (!Target->allowsLargerPreferedTypeAlignment())
     return ABIAlign;
 
-  // Double and long long should be naturally aligned if possible.
+  // Double (and, for targets supporting AIX `power` alignment, long double) and
+  // long long should be naturally aligned (despite requiring less alignment) if
+  // possible.
   if (const auto *CT = T->getAs<ComplexType>())
     T = CT->getElementType().getTypePtr();
   if (const auto *ET = T->getAs<EnumType>())
     T = ET->getDecl()->getIntegerType().getTypePtr();
   if (T->isSpecificBuiltinType(BuiltinType::Double) ||
       T->isSpecificBuiltinType(BuiltinType::LongLong) ||
-      T->isSpecificBuiltinType(BuiltinType::ULongLong))
+      T->isSpecificBuiltinType(BuiltinType::ULongLong) ||
+      (T->isSpecificBuiltinType(BuiltinType::LongDouble) &&
+       Target->defaultsToAIXPowerAlignment()))
     // Don't increase the alignment if an alignment attribute was specified on a
     // typedef declaration.
     if (!TI.AlignIsRequired)
       return std::max(ABIAlign, (unsigned)getTypeSize(T));
 
   return ABIAlign;
 }
 
 /// getTargetDefaultAlignForAttributeAligned - Return the default alignment
 /// for __attribute__((aligned)) on this target, to be used if no alignment
 /// value is specified.
 unsigned ASTContext::getTargetDefaultAlignForAttributeAligned() const {
   return getTargetInfo().getDefaultAlignForAttributeAligned();
 }
 
 /// getAlignOfGlobalVar - Return the alignment in bits that should be given
 /// to a global variable of the specified type.
 unsigned ASTContext::getAlignOfGlobalVar(QualType T) const {
   uint64_t TypeSize = getTypeSize(T.getTypePtr());
   return std::max(getTypeAlign(T), getTargetInfo().getMinGlobalAlign(TypeSize));
 }
 
 /// getAlignOfGlobalVarInChars - Return the alignment in characters that

clang/lib/AST/RecordLayout.cpp

if (CXXInfo) {
     Ctx.Deallocate(CXXInfo);
   }
   this->~ASTRecordLayout();
   Ctx.Deallocate(this);
 }
 
 ASTRecordLayout::ASTRecordLayout(const ASTContext &Ctx, CharUnits size,
                                  CharUnits alignment,
+                                 CharUnits preferredAlignment,
                                  CharUnits unadjustedAlignment,
                                  CharUnits requiredAlignment,
                                  CharUnits datasize,
                                  ArrayRef<uint64_t> fieldoffsets)
     : Size(size), DataSize(datasize), Alignment(alignment),
+      PreferredAlignment(preferredAlignment),
       UnadjustedAlignment(unadjustedAlignment),
       RequiredAlignment(requiredAlignment) {
   FieldOffsets.append(Ctx, fieldoffsets.begin(), fieldoffsets.end());
 }
 
 // Constructor for C++ records.
-ASTRecordLayout::ASTRecordLayout(const ASTContext &Ctx,
-                                 CharUnits size, CharUnits alignment,
-                                 CharUnits unadjustedAlignment,
-                                 CharUnits requiredAlignment,
-                                 bool hasOwnVFPtr, bool hasExtendableVFPtr,
-                                 CharUnits vbptroffset,
-                                 CharUnits datasize,
-                                 ArrayRef<uint64_t> fieldoffsets,
-                                 CharUnits nonvirtualsize,
-                                 CharUnits nonvirtualalignment,
-                                 CharUnits SizeOfLargestEmptySubobject,
-                                 const CXXRecordDecl *PrimaryBase,
-                                 bool IsPrimaryBaseVirtual,
-                                 const CXXRecordDecl *BaseSharingVBPtr,
-                                 bool EndsWithZeroSizedObject,
-                                 bool LeadsWithZeroSizedBase,
-                                 const BaseOffsetsMapTy& BaseOffsets,
-                                 const VBaseOffsetsMapTy& VBaseOffsets)
+ASTRecordLayout::ASTRecordLayout(
+    const ASTContext &Ctx, CharUnits size, CharUnits alignment,
+    CharUnits preferredAlignment, CharUnits unadjustedAlignment,
+    CharUnits requiredAlignment, bool hasOwnVFPtr, bool hasExtendableVFPtr,
+    CharUnits vbptroffset, CharUnits datasize, ArrayRef<uint64_t> fieldoffsets,
+    CharUnits nonvirtualsize, CharUnits nonvirtualalignment,
+    CharUnits preferrednvalignment, CharUnits SizeOfLargestEmptySubobject,
+    const CXXRecordDecl *PrimaryBase, bool IsPrimaryBaseVirtual,
+    const CXXRecordDecl *BaseSharingVBPtr, bool EndsWithZeroSizedObject,
+    bool LeadsWithZeroSizedBase, const BaseOffsetsMapTy &BaseOffsets,
+    const VBaseOffsetsMapTy &VBaseOffsets)
     : Size(size), DataSize(datasize), Alignment(alignment),
+      PreferredAlignment(preferredAlignment),
       UnadjustedAlignment(unadjustedAlignment),
-    RequiredAlignment(requiredAlignment), CXXInfo(new (Ctx) CXXRecordLayoutInfo)
-{
+      RequiredAlignment(requiredAlignment),
+      CXXInfo(new (Ctx) CXXRecordLayoutInfo) {
   FieldOffsets.append(Ctx, fieldoffsets.begin(), fieldoffsets.end());
 
   CXXInfo->PrimaryBase.setPointer(PrimaryBase);
   CXXInfo->PrimaryBase.setInt(IsPrimaryBaseVirtual);
   CXXInfo->NonVirtualSize = nonvirtualsize;
   CXXInfo->NonVirtualAlignment = nonvirtualalignment;
+  CXXInfo->PreferredNVAlignment = preferrednvalignment;
   CXXInfo->SizeOfLargestEmptySubobject = SizeOfLargestEmptySubobject;
   CXXInfo->BaseOffsets = BaseOffsets;
   CXXInfo->VBaseOffsets = VBaseOffsets;
   CXXInfo->HasOwnVFPtr = hasOwnVFPtr;
   CXXInfo->VBPtrOffset = vbptroffset;
   CXXInfo->HasExtendableVFPtr = hasExtendableVFPtr;
   CXXInfo->BaseSharingVBPtr = BaseSharingVBPtr;
   CXXInfo->EndsWithZeroSizedObject = EndsWithZeroSizedObject;

clang/lib/AST/RecordLayoutBuilder.cpp

 //=== RecordLayoutBuilder.cpp - Helper class for building record layouts ---==//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/AST/RecordLayout.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/ASTDiagnostic.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/VTableBuilder.h"
+#include "clang/AST/RecordLayout.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/MathExtras.h"
 
 using namespace clang;
 
 namespace {
protected:
   EmptySubobjectMap *EmptySubobjects;
 
   /// Size - The current size of the record layout.
   uint64_t Size;
 
   /// Alignment - The current alignment of the record layout.
   CharUnits Alignment;
 
+  /// PreferredAlignment - The preferred alignment of the record layout.
+  CharUnits PreferredAlignment;
+
   /// The alignment if attribute packed is not used.
   CharUnits UnpackedAlignment;
 
   /// \brief The maximum of the alignments of top-level members.
   CharUnits UnadjustedAlignment;
 
   SmallVector<uint64_t, 16> FieldOffsets;
 
protected:
   /// #pragma pack.
   CharUnits MaxFieldAlignment;
 
   /// DataSize - The data size of the record being laid out.
   uint64_t DataSize;
 
   CharUnits NonVirtualSize;
   CharUnits NonVirtualAlignment;
+  CharUnits PreferredNVAlignment;
 
   /// If we've laid out a field but not included its tail padding in Size yet,
   /// this is the size up to the end of that field.
   CharUnits PaddedFieldSize;
 
   /// PrimaryBase - the primary base class (if one exists) of the class
   /// we're laying out.
   const CXXRecordDecl *PrimaryBase;
 
   /// PrimaryBaseIsVirtual - Whether the primary base of the class we're laying
   /// out is virtual.
   bool PrimaryBaseIsVirtual;
 
   /// HasOwnVFPtr - Whether the class provides its own vtable/vftbl
   /// pointer, as opposed to inheriting one from a primary base class.
   bool HasOwnVFPtr;
 
   /// the flag of field offset changing due to packed attribute.
   bool HasPackedField;
 
+  /// HandledFirstNonOverlappingEmptyField - An auxiliary field used for AIX.
+  /// When there are OverlappingEmptyFields existing in the aggregate, the
+  /// flag shows if the following first non-empty or empty-but-non-overlapping
+  /// field has been handled, if any.
+  bool HandledFirstNonOverlappingEmptyField;
+
   typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
 
   /// Bases - base classes and their offsets in the record.
   BaseOffsetsMapTy Bases;
 
   // VBases - virtual base classes and their offsets in the record.
   ASTRecordLayout::VBaseOffsetsMapTy VBases;
 
   /// IndirectPrimaryBases - Virtual base classes, direct or indirect, that are
   /// primary base classes for some other direct or indirect base class.
   CXXIndirectPrimaryBaseSet IndirectPrimaryBases;
 
   /// FirstNearlyEmptyVBase - The first nearly empty virtual base class in
   /// inheritance graph order. Used for determining the primary base class.
   const CXXRecordDecl *FirstNearlyEmptyVBase;
 
   /// VisitedVirtualBases - A set of all the visited virtual bases, used to
   /// avoid visiting virtual bases more than once.
   llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBases;
 
   /// Valid if UseExternalLayout is true.
   ExternalLayout External;
 
   ItaniumRecordLayoutBuilder(const ASTContext &Context,
                              EmptySubobjectMap *EmptySubobjects)
       : Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
-        Alignment(CharUnits::One()), UnpackedAlignment(CharUnits::One()),
-        UnadjustedAlignment(CharUnits::One()),
-        UseExternalLayout(false), InferAlignment(false), Packed(false),
-        IsUnion(false), IsMac68kAlign(false), IsMsStruct(false),
-        UnfilledBitsInLastUnit(0), LastBitfieldTypeSize(0),
-        MaxFieldAlignment(CharUnits::Zero()), DataSize(0),
-        NonVirtualSize(CharUnits::Zero()),
+        Alignment(CharUnits::One()), PreferredAlignment(CharUnits::One()),
+        UnpackedAlignment(CharUnits::One()),
+        UnadjustedAlignment(CharUnits::One()), UseExternalLayout(false),
+        InferAlignment(false), Packed(false), IsUnion(false),
+        IsMac68kAlign(false), IsMsStruct(false), UnfilledBitsInLastUnit(0),
+        LastBitfieldTypeSize(0), MaxFieldAlignment(CharUnits::Zero()),
+        DataSize(0), NonVirtualSize(CharUnits::Zero()),
         NonVirtualAlignment(CharUnits::One()),
+        PreferredNVAlignment(CharUnits::One()),
         PaddedFieldSize(CharUnits::Zero()), PrimaryBase(nullptr),
-        PrimaryBaseIsVirtual(false), HasOwnVFPtr(false),
-        HasPackedField(false), FirstNearlyEmptyVBase(nullptr) {}
+        PrimaryBaseIsVirtual(false), HasOwnVFPtr(false), HasPackedField(false),
+        HandledFirstNonOverlappingEmptyField(false),
+        FirstNearlyEmptyVBase(nullptr) {}
 
   void Layout(const RecordDecl *D);
   void Layout(const CXXRecordDecl *D);
   void Layout(const ObjCInterfaceDecl *D);
 
   void LayoutFields(const RecordDecl *D);
   void LayoutField(const FieldDecl *D, bool InsertExtraPadding);
   void LayoutWideBitField(uint64_t FieldSize, uint64_t TypeSize,
protected:
 
   /// InitializeLayout - Initialize record layout for the given record decl.
   void InitializeLayout(const Decl *D);
 
   /// FinishLayout - Finalize record layout. Adjust record size based on the
   /// alignment.
   void FinishLayout(const NamedDecl *D);
 
-  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment);
+  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment,
+                       CharUnits PreferredAlignment);
+  void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
+    UpdateAlignment(NewAlignment, UnpackedNewAlignment, NewAlignment);
+  }
   void UpdateAlignment(CharUnits NewAlignment) {
-    UpdateAlignment(NewAlignment, NewAlignment);
+    UpdateAlignment(NewAlignment, NewAlignment, NewAlignment);
   }
 
   /// Retrieve the externally-supplied field offset for the given
   /// field.
   ///
   /// \param Field The field whose offset is being queried.
   /// \param ComputedOffset The offset that we've computed for this field.
   uint64_t updateExternalFieldOffset(const FieldDecl *Field,
protected:
   void setDataSize(uint64_t NewSize) { DataSize = NewSize; }
 
   ItaniumRecordLayoutBuilder(const ItaniumRecordLayoutBuilder &) = delete;
   void operator=(const ItaniumRecordLayoutBuilder &) = delete;
 };
 } // end anonymous namespace
 
 void ItaniumRecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
   for (const auto &I : RD->bases()) {
     assert(!I.getType()->isDependentType() &&
            "Cannot layout class with dependent bases.");
 
     const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
 
     // Check if this is a nearly empty virtual base.
     if (I.isVirtual() && Context.isNearlyEmpty(Base)) {
       // If it's not an indirect primary base, then we've found our primary
if (!MaxFieldAlignment.isZero()) {
     BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
     UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
   }
 
   // Round up the current record size to pointer alignment.
   setSize(getSize().alignTo(BaseAlign));
 
   // Update the alignment.
-  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+  UpdateAlignment(BaseAlign, UnpackedBaseAlign, BaseAlign);
 }
 
 void ItaniumRecordLayoutBuilder::LayoutNonVirtualBases(
     const CXXRecordDecl *RD) {
   // Then, determine the primary base class.
   DeterminePrimaryBase(RD);
 
   // Compute base subobject info.
void ItaniumRecordLayoutBuilder::LayoutNonVirtualBases(
   } else if (RD->isDynamicClass()) {
     assert(DataSize == 0 && "Vtable pointer must be at offset zero!");
     CharUnits PtrWidth =
       Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
     CharUnits PtrAlign =
       Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
     EnsureVTablePointerAlignment(PtrAlign);
     HasOwnVFPtr = true;
+
+    assert(!IsUnion && "Unions cannot be dynamic classes.");
+    HandledFirstNonOverlappingEmptyField = true;
+
     setSize(getSize() + PtrWidth);
     setDataSize(getSize());
   }
 
   // Now lay out the non-virtual bases.
   for (const auto &I : RD->bases()) {
 
     // Ignore virtual bases.
     if (I.isVirtual())
       continue;
void ItaniumRecordLayoutBuilder::LayoutVirtualBase(
   VBases.insert(std::make_pair(Base->Class,
                        ASTRecordLayout::VBaseInfo(Offset, false)));
 
   AddPrimaryVirtualBaseOffsets(Base, Offset);
 }
 
 CharUnits
 ItaniumRecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
-  const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base->Class);
-
+  assert(!IsUnion && "Unions cannot have base classes.");
 
+  const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base->Class);
   CharUnits Offset;
 
   // Query the external layout to see if it provides an offset.
   bool HasExternalLayout = false;
   if (UseExternalLayout) {
     // FIXME: This appears to be reversed.
     if (Base->IsVirtual)
       HasExternalLayout = External.getExternalNVBaseOffset(Base->Class, Offset);
     else
       HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
   }
 
+  auto getBaseOrPreferredBaseAlignFromUnpacked = [&](CharUnits UnpackedAlign) {
     // Clang <= 6 incorrectly applied the 'packed' attribute to base classes.
     // Per GCC's documentation, it only applies to non-static data members.
-  CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
-  CharUnits BaseAlign =
-      (Packed && ((Context.getLangOpts().getClangABICompat() <=
+    return (Packed && ((Context.getLangOpts().getClangABICompat() <=
                         LangOptions::ClangABI::Ver6) ||
-                  Context.getTargetInfo().getTriple().isPS4()))
+                       Context.getTargetInfo().getTriple().isPS4() ||
+                       Context.getTargetInfo().getTriple().isOSAIX()))
                ? CharUnits::One()
-          : UnpackedBaseAlign;
+               : UnpackedAlign;
+  };
+
+  CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
+  CharUnits UnpackedPreferredBaseAlign = Layout.getPreferredNVAlignment();
+  CharUnits BaseAlign =
+      getBaseOrPreferredBaseAlignFromUnpacked(UnpackedBaseAlign);
+  CharUnits PreferredBaseAlign =
+      getBaseOrPreferredBaseAlignFromUnpacked(UnpackedPreferredBaseAlign);
+
+  bool DefaultsToAIXPowerAlignment =
+      Context.getTargetInfo().defaultsToAIXPowerAlignment();
+  if (DefaultsToAIXPowerAlignment) {
+    bool IsFirstNonEmptyBase = false;
+    if (!Base->Class->isEmpty() && !HandledFirstNonOverlappingEmptyField) {
+      IsFirstNonEmptyBase = true;
+      // By handling a base class that is not empty, we're handling the
+      // "first (inherited) member".
+      HandledFirstNonOverlappingEmptyField = true;
+    }
+
+    // AIX `power` alignment does not apply the preferred alignment for
+    // non-union classes if the source of the alignment (the current base in
+    // this context) follows introduction of the first subobject with
+    // exclusively allocated space or zero-extent array.
+    if (!IsFirstNonEmptyBase) {
+      UnpackedPreferredBaseAlign = UnpackedBaseAlign;
+      PreferredBaseAlign = BaseAlign;
+    }
+  }
 
+  CharUnits UnpackedAlignTo = !DefaultsToAIXPowerAlignment
+                                  ? UnpackedBaseAlign
+                                  : UnpackedPreferredBaseAlign;
   // If we have an empty base class, try to place it at offset 0.
   if (Base->Class->isEmpty() &&
       (!HasExternalLayout || Offset == CharUnits::Zero()) &&
       EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
     setSize(std::max(getSize(), Layout.getSize()));
-    UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+    UpdateAlignment(BaseAlign, UnpackedAlignTo, PreferredBaseAlign);
 
     return CharUnits::Zero();
   }
 
-  // The maximum field alignment overrides base align.
+  // The maximum field alignment overrides the base align/(AIX-only) preferred
+  // base align.
   if (!MaxFieldAlignment.isZero()) {
     BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
-    UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
+    PreferredBaseAlign = std::min(PreferredBaseAlign, MaxFieldAlignment);
+    UnpackedAlignTo = std::min(UnpackedAlignTo, MaxFieldAlignment);
   }
 
+  CharUnits AlignTo =
+      !DefaultsToAIXPowerAlignment ? BaseAlign : PreferredBaseAlign;
   if (!HasExternalLayout) {
     // Round up the current record size to the base's alignment boundary.
-    Offset = getDataSize().alignTo(BaseAlign);
+    Offset = getDataSize().alignTo(AlignTo);
 
     // Try to place the base.
     while (!EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset))
-      Offset += BaseAlign;
+      Offset += AlignTo;
   } else {
     bool Allowed = EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset);
     (void)Allowed;
     assert(Allowed && "Base subobject externally placed at overlapping offset");
 
-    if (InferAlignment && Offset < getDataSize().alignTo(BaseAlign)) {
+    if (InferAlignment && Offset < getDataSize().alignTo(AlignTo)) {
       // The externally-supplied base offset is before the base offset we
       // computed. Assume that the structure is packed.
       Alignment = CharUnits::One();
       InferAlignment = false;
     }
   }
 
   if (!Base->Class->isEmpty()) {
     // Update the data size.
     setDataSize(Offset + Layout.getNonVirtualSize());
 
     setSize(std::max(getSize(), getDataSize()));
   } else
     setSize(std::max(getSize(), Offset + Layout.getSize()));
 
   // Remember max struct/class alignment.
-  UpdateAlignment(BaseAlign, UnpackedBaseAlign);
+  UpdateAlignment(BaseAlign, UnpackedAlignTo, PreferredBaseAlign);
 
   return Offset;
 }
 
 void ItaniumRecordLayoutBuilder::InitializeLayout(const Decl *D) {
   if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
     IsUnion = RD->isUnion();
     IsMsStruct = RD->isMsStruct(Context);
void ItaniumRecordLayoutBuilder::InitializeLayout(const Decl *D) {
   // mac68k alignment supersedes maximum field alignment and attribute aligned,
   // and forces all structures to have 2-byte alignment. The IBM docs on it
   // allude to additional (more complicated) semantics, especially with regard
   // to bit-fields, but gcc appears not to follow that.
   if (D->hasAttr<AlignMac68kAttr>()) {
     IsMac68kAlign = true;
     MaxFieldAlignment = CharUnits::fromQuantity(2);
     Alignment = CharUnits::fromQuantity(2);
+    PreferredAlignment = CharUnits::fromQuantity(2);
   } else {
     if (const MaxFieldAlignmentAttr *MFAA = D->getAttr<MaxFieldAlignmentAttr>())
       MaxFieldAlignment = Context.toCharUnitsFromBits(MFAA->getAlignment());
 
     if (unsigned MaxAlign = D->getMaxAlignment())
       UpdateAlignment(Context.toCharUnitsFromBits(MaxAlign));
   }
 
   // If there is an external AST source, ask it for the various offsets.
   if (const RecordDecl *RD = dyn_cast<RecordDecl>(D))
     if (ExternalASTSource *Source = Context.getExternalSource()) {
       UseExternalLayout = Source->layoutRecordType(
           RD, External.Size, External.Align, External.FieldOffsets,
           External.BaseOffsets, External.VirtualBaseOffsets);
 
       // Update based on external alignment.
       if (UseExternalLayout) {
         if (External.Align > 0) {
           Alignment = Context.toCharUnitsFromBits(External.Align);
+          PreferredAlignment = Context.toCharUnitsFromBits(External.Align);
         } else {
           // The external source didn't have alignment information; infer it.
           InferAlignment = true;
         }
       }
     }
 }
 
void ItaniumRecordLayoutBuilder::Layout(const CXXRecordDecl *RD) {
   // Lay out the vtable and the non-virtual bases.
   LayoutNonVirtualBases(RD);
 
   LayoutFields(RD);
 
   NonVirtualSize = Context.toCharUnitsFromBits(
       llvm::alignTo(getSizeInBits(), Context.getTargetInfo().getCharAlign()));
   NonVirtualAlignment = Alignment;
+  PreferredNVAlignment = PreferredAlignment;
 
   // Lay out the virtual bases and add the primary virtual base offsets.
   LayoutVirtualBases(RD, RD);
 
   // Finally, round the size of the total struct up to the alignment
   // of the struct itself.
   FinishLayout(RD);
 
void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   UnadjustedAlignment =
       std::max(UnadjustedAlignment, Context.toCharUnitsFromBits(FieldAlign));
   UpdateAlignment(Context.toCharUnitsFromBits(FieldAlign),
                   Context.toCharUnitsFromBits(UnpackedFieldAlign));
 }
 
 void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
                                              bool InsertExtraPadding) {
+  auto *FieldClass = D->getType()->getAsCXXRecordDecl();
+  bool PotentiallyOverlapping = D->hasAttr<NoUniqueAddressAttr>() && FieldClass;
+  bool IsOverlappingEmptyField =
+      PotentiallyOverlapping && FieldClass->isEmpty();
+
+  CharUnits FieldOffset =
+      (IsUnion || IsOverlappingEmptyField) ? CharUnits::Zero() : getDataSize();
+
+  bool DefaultsToAIXPowerAlignment =
+      Context.getTargetInfo().defaultsToAIXPowerAlignment();
+  bool FoundFirstNonOverlappingEmptyFieldForAIX = false;
+  if (DefaultsToAIXPowerAlignment && !HandledFirstNonOverlappingEmptyField) {
+    assert(FieldOffset == CharUnits::Zero() &&
+           "The first non-overlapping empty field should have been handled.");
+
+    if (!IsOverlappingEmptyField) {
+      FoundFirstNonOverlappingEmptyFieldForAIX = true;
+
+      // We're going to handle the "first member" based on
+      // `FoundFirstNonOverlappingEmptyFieldForAIX` during the current
+      // invocation of this function; record it as handled for future
+      // invocations (except for unions, because the current field does not
+      // represent all "firsts").
+      HandledFirstNonOverlappingEmptyField = !IsUnion;
+    }
+  }
+
   if (D->isBitField()) {
     LayoutBitField(D);
     return;
   }
 
   uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
-
   // Reset the unfilled bits.
   UnfilledBitsInLastUnit = 0;
   LastBitfieldTypeSize = 0;
 
-  auto *FieldClass = D->getType()->getAsCXXRecordDecl();
-  bool PotentiallyOverlapping = D->hasAttr<NoUniqueAddressAttr>() && FieldClass;
-  bool IsOverlappingEmptyField = PotentiallyOverlapping && FieldClass->isEmpty();
   bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
 
-  CharUnits FieldOffset = (IsUnion || IsOverlappingEmptyField)
-                              ? CharUnits::Zero()
-                              : getDataSize();
+  bool AlignIsRequired = false;
   CharUnits FieldSize;
   CharUnits FieldAlign;
   // The amount of this class's dsize occupied by the field.
   // This is equal to FieldSize unless we're permitted to pack
   // into the field's tail padding.
   CharUnits EffectiveFieldSize;
 
+  auto setDeclInfo = [&](bool IsIncompleteArrayType) {
+    TypeInfo TI = Context.getTypeInfo(D->getType());
+    FieldAlign = Context.toCharUnitsFromBits(TI.Align);
+    // Flexible array members don't have any size, but they have to be
+    // aligned appropriately for their element type.
+    EffectiveFieldSize = FieldSize =
+        IsIncompleteArrayType ? CharUnits::Zero()
+                              : Context.toCharUnitsFromBits(TI.Width);
+    AlignIsRequired = TI.AlignIsRequired;
+  };
+
   if (D->getType()->isIncompleteArrayType()) {
-    // This is a flexible array member; we can't directly
-    // query getTypeInfo about these, so we figure it out here.
-    // Flexible array members don't have any size, but they
-    // have to be aligned appropriately for their element type.
-    EffectiveFieldSize = FieldSize = CharUnits::Zero();
-    const ArrayType* ATy = Context.getAsArrayType(D->getType());
-    FieldAlign = Context.getTypeAlignInChars(ATy->getElementType());
+    setDeclInfo(true /* IsIncompleteArrayType */);
   } else if (const ReferenceType *RT = D->getType()->getAs<ReferenceType>()) {
     unsigned AS = Context.getTargetAddressSpace(RT->getPointeeType());
-    EffectiveFieldSize = FieldSize =
-      Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(AS));
-    FieldAlign =
-      Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(AS));
-  } else {
-    std::pair<CharUnits, CharUnits> FieldInfo =
-      Context.getTypeInfoInChars(D->getType());
-    EffectiveFieldSize = FieldSize = FieldInfo.first;
-    FieldAlign = FieldInfo.second;
+    EffectiveFieldSize = FieldSize = Context.toCharUnitsFromBits(
+        Context.getTargetInfo().getPointerWidth(AS));
+    FieldAlign = Context.toCharUnitsFromBits(
+        Context.getTargetInfo().getPointerAlign(AS));
+  } else {
+    setDeclInfo(false /* IsIncompleteArrayType */);
 
     // A potentially-overlapping field occupies its dsize or nvsize, whichever
     // is larger.
     if (PotentiallyOverlapping) {
       const ASTRecordLayout &Layout = Context.getASTRecordLayout(FieldClass);
       EffectiveFieldSize =
           std::max(Layout.getNonVirtualSize(), Layout.getDataSize());
     }
if (IsMsStruct) {
         }
         if (TypeSize > FieldAlign &&
             llvm::isPowerOf2_64(TypeSize.getQuantity()))
           FieldAlign = TypeSize;
       }
     }
   }
 
+  // The AIX `power` alignment rules apply the natural alignment of the
+  // "first member" if it is of a floating-point data type (or is an aggregate
+  // whose recursively "first" member or element is such a type). The alignment
+  // associated with these types for subsequent members use an alignment value
+  // where the floating-point data type is considered to have 4-byte alignment.
+  //
+  // For the purposes of the foregoing: vtable pointers, non-empty base classes,
+  // and zero-width bit-fields count as prior members; members of empty class
+  // types marked `no_unique_address` are not considered to be prior members.
+  CharUnits PreferredAlign = FieldAlign;
+  if (DefaultsToAIXPowerAlignment && !AlignIsRequired &&
+      FoundFirstNonOverlappingEmptyFieldForAIX) {
+    auto performBuiltinTypeAlignmentUpgrade = [&](const BuiltinType *BTy) {
+      if (BTy->getKind() == BuiltinType::Double ||
+          BTy->getKind() == BuiltinType::LongDouble) {
+        assert(PreferredAlign == CharUnits::fromQuantity(4) &&
+               "No need to upgrade the alignment value.");
+        PreferredAlign = CharUnits::fromQuantity(8);
+      }
+    };
+
+    const Type *Ty = D->getType()->getBaseElementTypeUnsafe();
+    if (const ComplexType *CTy = Ty->getAs<ComplexType>()) {
+      performBuiltinTypeAlignmentUpgrade(CTy->getElementType()->castAs<BuiltinType>());
+    } else if (const BuiltinType *BTy = Ty->getAs<BuiltinType>()) {
+      performBuiltinTypeAlignmentUpgrade(BTy);
+    } else if (const RecordType *RT = Ty->getAs<RecordType>()) {
+      const RecordDecl *RD = RT->getDecl();
+      assert(RD && "Expected non-null RecordDecl.");
+      const ASTRecordLayout &FieldRecord = Context.getASTRecordLayout(RD);
+      PreferredAlign = FieldRecord.getPreferredAlignment();
+    }
+  }
+
   // The align if the field is not packed. This is to check if the attribute
   // was unnecessary (-Wpacked).
-  CharUnits UnpackedFieldAlign = FieldAlign;
+  CharUnits UnpackedFieldAlign =
+      !DefaultsToAIXPowerAlignment ? FieldAlign : PreferredAlign;
   CharUnits UnpackedFieldOffset = FieldOffset;
 
-  if (FieldPacked)
+  if (FieldPacked) {
     FieldAlign = CharUnits::One();
+    PreferredAlign = CharUnits::One();
+  }
   CharUnits MaxAlignmentInChars =
       Context.toCharUnitsFromBits(D->getMaxAlignment());
   FieldAlign = std::max(FieldAlign, MaxAlignmentInChars);
+  PreferredAlign = std::max(PreferredAlign, MaxAlignmentInChars);
   UnpackedFieldAlign = std::max(UnpackedFieldAlign, MaxAlignmentInChars);
 
   // The maximum field alignment overrides the aligned attribute.
   if (!MaxFieldAlignment.isZero()) {
     FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
+    PreferredAlign = std::min(PreferredAlign, MaxFieldAlignment);
     UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
   }
 
+  CharUnits AlignTo =
+      !DefaultsToAIXPowerAlignment ? FieldAlign : PreferredAlign;
   // Round up the current record size to the field's alignment boundary.
-  FieldOffset = FieldOffset.alignTo(FieldAlign);
+  FieldOffset = FieldOffset.alignTo(AlignTo);
   UnpackedFieldOffset = UnpackedFieldOffset.alignTo(UnpackedFieldAlign);
 
   if (UseExternalLayout) {
     FieldOffset = Context.toCharUnitsFromBits(
-                    updateExternalFieldOffset(D, Context.toBits(FieldOffset)));
 
     if (!IsUnion && EmptySubobjects) {
       // Record the fact that we're placing a field at this offset.
       bool Allowed = EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset);
       (void)Allowed;
       assert(Allowed && "Externally-placed field cannot be placed here");
     }
   } else {
     if (!IsUnion && EmptySubobjects) {
       // Check if we can place the field at this offset.
       while (!EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset)) {
         // We couldn't place the field at the offset. Try again at a new offset.
         // We try offset 0 (for an empty field) and then dsize(C) onwards.
         if (FieldOffset == CharUnits::Zero() &&
             getDataSize() != CharUnits::Zero())
-          FieldOffset = getDataSize().alignTo(FieldAlign);
+          FieldOffset = getDataSize().alignTo(AlignTo);
         else
-          FieldOffset += FieldAlign;
+          FieldOffset += AlignTo;
       }
     }
   }
 
   // Place this field at the current location.
   FieldOffsets.push_back(Context.toBits(FieldOffset));
 
   if (!UseExternalLayout)
if (!IsOverlappingEmptyField) {
 
     PaddedFieldSize = std::max(PaddedFieldSize, FieldOffset + FieldSize);
     setSize(std::max(getSizeInBits(), getDataSizeInBits()));
   } else {
     setSize(std::max(getSizeInBits(),
                      (uint64_t)Context.toBits(FieldOffset + FieldSize)));
   }
 
-  // Remember max struct/class alignment.
+  // Remember max struct/class ABI-specified alignment.
   UnadjustedAlignment = std::max(UnadjustedAlignment, FieldAlign);
-  UpdateAlignment(FieldAlign, UnpackedFieldAlign);
+  UpdateAlignment(FieldAlign, UnpackedFieldAlign, PreferredAlign);
 }
 
 void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
   // In C++, records cannot be of size 0.
   if (Context.getLangOpts().CPlusPlus && getSizeInBits() == 0) {
     if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
       // Compatibility with gcc requires a class (pod or non-pod)
       // which is not empty but of size 0; such as having fields of
void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
   // size.
   setSize(std::max(getSizeInBits(), (uint64_t)Context.toBits(PaddedFieldSize)));
 
   // Finally, round the size of the record up to the alignment of the
   // record itself.
   uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastUnit;
   uint64_t UnpackedSizeInBits =
       llvm::alignTo(getSizeInBits(), Context.toBits(UnpackedAlignment));
-  uint64_t RoundedSize =
-      llvm::alignTo(getSizeInBits(), Context.toBits(Alignment));
+
+  uint64_t RoundedSize = llvm::alignTo(
+      getSizeInBits(),
+      Context.toBits(!Context.getTargetInfo().defaultsToAIXPowerAlignment()
+                         ? Alignment
+                         : PreferredAlignment));
 
   if (UseExternalLayout) {
     // If we're inferring alignment, and the external size is smaller than
     // our size after we've rounded up to alignment, conservatively set the
     // alignment to 1.
     if (InferAlignment && External.Size < RoundedSize) {
       Alignment = CharUnits::One();
+      PreferredAlignment = CharUnits::One();
       InferAlignment = false;
     }
     setSize(External.Size);
     return;
   }
 
   // Set the size to the final size.
   setSize(RoundedSize);
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
     if (Packed && UnpackedAlignment <= Alignment &&
         UnpackedSizeInBits == getSizeInBits() && !HasPackedField)
       Diag(D->getLocation(), diag::warn_unnecessary_packed)
           << Context.getTypeDeclType(RD);
   }
 }
 
 void ItaniumRecordLayoutBuilder::UpdateAlignment(
-    CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
+    CharUnits NewAlignment, CharUnits UnpackedNewAlignment,
+    CharUnits PreferredNewAlignment) {
   // The alignment is not modified when using 'mac68k' alignment or when
   // we have an externally-supplied layout that also provides overall alignment.
   if (IsMac68kAlign || (UseExternalLayout && !InferAlignment))
     return;
 
   if (NewAlignment > Alignment) {
     assert(llvm::isPowerOf2_64(NewAlignment.getQuantity()) &&
            "Alignment not a power of 2");
     Alignment = NewAlignment;
   }
 
   if (UnpackedNewAlignment > UnpackedAlignment) {
     assert(llvm::isPowerOf2_64(UnpackedNewAlignment.getQuantity()) &&
            "Alignment not a power of 2");
     UnpackedAlignment = UnpackedNewAlignment;
   }
+
+  if (PreferredNewAlignment > PreferredAlignment) {
+    assert(llvm::isPowerOf2_64(PreferredNewAlignment.getQuantity()) &&
+           "Alignment not a power of 2");
+    PreferredAlignment = PreferredNewAlignment;
+  }
 }
 
 uint64_t
 ItaniumRecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
                                                       uint64_t ComputedOffset) {
   uint64_t ExternalFieldOffset = External.getExternalFieldOffset(Field);
 
   if (InferAlignment && ExternalFieldOffset < ComputedOffset) {
     // The externally-supplied field offset is before the field offset we
     // computed. Assume that the structure is packed.
     Alignment = CharUnits::One();
+    PreferredAlignment = CharUnits::One();
     InferAlignment = false;
   }
 
   // Use the externally-supplied field offset.
   return ExternalFieldOffset;
 }
 
 /// Get diagnostic %select index for tag kind for
ASTContext::getASTRecordLayout(const RecordDecl *D) const {
   const ASTRecordLayout *NewEntry = nullptr;
 
   if (isMsLayout(*this)) {
     MicrosoftRecordLayoutBuilder Builder(*this);
     if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
       Builder.cxxLayout(RD);
       NewEntry = new (*this) ASTRecordLayout(
           *this, Builder.Size, Builder.Alignment, Builder.Alignment,
-          Builder.RequiredAlignment,
-          Builder.HasOwnVFPtr, Builder.HasOwnVFPtr || Builder.PrimaryBase,
-          Builder.VBPtrOffset, Builder.DataSize, Builder.FieldOffsets,
-          Builder.NonVirtualSize, Builder.Alignment, CharUnits::Zero(),
+          Builder.Alignment, Builder.RequiredAlignment, Builder.HasOwnVFPtr,
+          Builder.HasOwnVFPtr || Builder.PrimaryBase, Builder.VBPtrOffset,
+          Builder.DataSize, Builder.FieldOffsets, Builder.NonVirtualSize,
+          Builder.Alignment, Builder.Alignment, CharUnits::Zero(),
           Builder.PrimaryBase, false, Builder.SharedVBPtrBase,
           Builder.EndsWithZeroSizedObject, Builder.LeadsWithZeroSizedBase,
           Builder.Bases, Builder.VBases);
     } else {
       Builder.layout(D);
       NewEntry = new (*this) ASTRecordLayout(
           *this, Builder.Size, Builder.Alignment, Builder.Alignment,
-          Builder.RequiredAlignment,
-          Builder.Size, Builder.FieldOffsets);
+          Builder.Alignment, Builder.RequiredAlignment, Builder.Size,
+          Builder.FieldOffsets);
     }
   } else {
     if (const auto *RD = dyn_cast<CXXRecordDecl>(D)) {
       EmptySubobjectMap EmptySubobjects(*this, RD);
       ItaniumRecordLayoutBuilder Builder(*this, &EmptySubobjects);
       Builder.Layout(RD);
 
       // In certain situations, we are allowed to lay out objects in the
       // tail-padding of base classes.  This is ABI-dependent.
       // FIXME: this should be stored in the record layout.
       bool skipTailPadding =
           mustSkipTailPadding(getTargetInfo().getCXXABI(), RD);
 
       // FIXME: This should be done in FinalizeLayout.
       CharUnits DataSize =
           skipTailPadding ? Builder.getSize() : Builder.getDataSize();
       CharUnits NonVirtualSize =
           skipTailPadding ? DataSize : Builder.NonVirtualSize;
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
+          *this, Builder.getSize(), Builder.Alignment,
+          Builder.PreferredAlignment, Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
           Builder.Alignment, Builder.HasOwnVFPtr, RD->isDynamicClass(),
           CharUnits::fromQuantity(-1), DataSize, Builder.FieldOffsets,
           NonVirtualSize, Builder.NonVirtualAlignment,
+          Builder.PreferredNVAlignment,
           EmptySubobjects.SizeOfLargestEmptySubobject, Builder.PrimaryBase,
           Builder.PrimaryBaseIsVirtual, nullptr, false, false, Builder.Bases,
           Builder.VBases);
     } else {
       ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
       Builder.Layout(D);
 
       NewEntry = new (*this) ASTRecordLayout(
-          *this, Builder.getSize(), Builder.Alignment, Builder.UnadjustedAlignment,
+          *this, Builder.getSize(), Builder.Alignment,
+          Builder.PreferredAlignment, Builder.UnadjustedAlignment,
           /*RequiredAlignment : used by MS-ABI)*/
           Builder.Alignment, Builder.getSize(), Builder.FieldOffsets);
     }
   }
 
   ASTRecordLayouts[D] = NewEntry;
 
   if (getLangOpts().DumpRecordLayouts) {
if (Impl) {
     // frequently.
     if (SynthCount == 0)
       return getObjCLayout(D, nullptr);
   }
 
   ItaniumRecordLayoutBuilder Builder(*this, /*EmptySubobjects=*/nullptr);
   Builder.Layout(D);
 
-  const ASTRecordLayout *NewEntry =
-    new (*this) ASTRecordLayout(*this, Builder.getSize(),
-                                Builder.Alignment,
-                                Builder.UnadjustedAlignment,
-                                /*RequiredAlignment : used by MS-ABI)*/
-                                Builder.Alignment,
-                                Builder.getDataSize(),
-                                Builder.FieldOffsets);
+  const ASTRecordLayout *NewEntry = new (*this) ASTRecordLayout(
+      *this, Builder.getSize(), Builder.Alignment, Builder.PreferredAlignment,
+      Builder.Alignment, Builder.getDataSize(), Builder.FieldOffsets);
 
   ObjCLayouts[Key] = NewEntry;
 
   return *NewEntry;
 }
 
 static void PrintOffset(raw_ostream &OS,
                         CharUnits Offset, unsigned IndentLevel) {
static void DumpRecordLayout(raw_ostream &OS, const RecordDecl *RD,
 
   if (!PrintSizeInfo) return;
 
   PrintIndentNoOffset(OS, IndentLevel - 1);
   OS << "[sizeof=" << Layout.getSize().getQuantity();
   if (CXXRD && !isMsLayout(C))
     OS << ", dsize=" << Layout.getDataSize().getQuantity();
   OS << ", align=" << Layout.getAlignment().getQuantity();
+  if (C.getTargetInfo().defaultsToAIXPowerAlignment())
+    OS << ", preferredalign=" << Layout.getPreferredAlignment().getQuantity();
 
   if (CXXRD) {
     OS << ",\n";
     PrintIndentNoOffset(OS, IndentLevel - 1);
     OS << " nvsize=" << Layout.getNonVirtualSize().getQuantity();
     OS << ", nvalign=" << Layout.getNonVirtualAlignment().getQuantity();
+    if (C.getTargetInfo().defaultsToAIXPowerAlignment())
+      OS << ", preferrednvalign="
+         << Layout.getPreferredNVAlignment().getQuantity();
   }
   OS << "]\n";
 }
 
-void ASTContext::DumpRecordLayout(const RecordDecl *RD,
-                                  raw_ostream &OS,
+void ASTContext::DumpRecordLayout(const RecordDecl *RD, raw_ostream &OS,
                                   bool Simple) const {
   if (!Simple) {
     ::DumpRecordLayout(OS, RD, *this, CharUnits(), 0, nullptr,
-                       /*PrintSizeInfo*/true,
+                       /*PrintSizeInfo*/ true,
                        /*IncludeVirtualBases=*/true);
     return;
   }
 
   // The "simple" format is designed to be parsed by the
   // layout-override testing code.  There shouldn't be any external
   // uses of this format --- when LLDB overrides a layout, it sets up
   // the data structures directly --- so feel free to adjust this as
   // you like as long as you also update the rudimentary parser for it
   // in libFrontend.
 
   const ASTRecordLayout &Info = getASTRecordLayout(RD);
   OS << "Type: " << getTypeDeclType(RD).getAsString() << "\n";
   OS << "\nLayout: ";
   OS << "<ASTRecordLayout\n";
   OS << "  Size:" << toBits(Info.getSize()) << "\n";
   if (!isMsLayout(*this))
     OS << "  DataSize:" << toBits(Info.getDataSize()) << "\n";
   OS << "  Alignment:" << toBits(Info.getAlignment()) << "\n";
+  if (Target->defaultsToAIXPowerAlignment())
+    OS << "  PreferredAlignment:" << toBits(Info.getPreferredAlignment())
+       << "\n";
   OS << "  FieldOffsets: [";
   for (unsigned i = 0, e = Info.getFieldCount(); i != e; ++i) {
-    if (i) OS << ", ";
+    if (i)
+      OS << ", ";
     OS << Info.getFieldOffset(i);
   }
   OS << "]>\n";
 }

clang/lib/Basic/Targets/OSTargets.h

if (this->PointerWidth == 64) {
       this->WCharType = this->UnsignedShort;
     }
     this->UseZeroLengthBitfieldAlignment = true;
   }
 
   // AIX sets FLT_EVAL_METHOD to be 1.
   unsigned getFloatEvalMethod() const override { return 1; }
   bool hasInt128Type() const override { return false; }
+
+  bool defaultsToAIXPowerAlignment() const override { return true; }
 };
 
 void addWindowsDefines(const llvm::Triple &Triple, const LangOptions &Opts,
                        MacroBuilder &Builder);
 
 // Windows target
 template <typename Target>
 class LLVM_LIBRARY_VISIBILITY WindowsTargetInfo : public OSTargetInfo<Target> {

clang/lib/Basic/Targets/PPC.h

case llvm::Triple::AIX:
       IntPtrType = SignedLong;
       SuitableAlign = 64;
       break;
     default:
       break;
     }
 
     if (Triple.isOSFreeBSD() || Triple.isOSNetBSD() || Triple.isOSOpenBSD() ||
-        Triple.getOS() == llvm::Triple::AIX || Triple.isMusl()) {
+        Triple.isMusl()) {
       LongDoubleWidth = LongDoubleAlign = 64;
       LongDoubleFormat = &llvm::APFloat::IEEEdouble();
+    } else if (Triple.isOSAIX()) {
+      LongDoubleWidth = 64;
+      LongDoubleAlign = DoubleAlign = 32;
+      LongDoubleFormat = &llvm::APFloat::IEEEdouble();
     }
 
     // PPC32 supports atomics up to 4 bytes.
     MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 32;
   }
 
   BuiltinVaListKind getBuiltinVaListKind() const override {
     // This is the ELF definition, and is overridden by the Darwin sub-target
     return TargetInfo::PowerABIBuiltinVaList;
   }
 };
if (Triple.isOSAIX()) {
       SuitableAlign = 64;
     } else if ((Triple.getArch() == llvm::Triple::ppc64le)) {
       resetDataLayout("e-m:e-i64:64-n32:64");
       ABI = "elfv2";
     } else {
       resetDataLayout("E-m:e-i64:64-n32:64");
       ABI = "elfv1";
     }
 
-    if (Triple.isOSFreeBSD() || Triple.getOS() == llvm::Triple::AIX ||
-        Triple.isMusl()) {
+    if (Triple.isOSFreeBSD() || Triple.isMusl()) {
       LongDoubleWidth = LongDoubleAlign = 64;
       LongDoubleFormat = &llvm::APFloat::IEEEdouble();
+    } else if (Triple.isOSAIX()) {
+      SuitableAlign = 64;
+      LongDoubleWidth = 64;
+      LongDoubleAlign = DoubleAlign = 32;
+      LongDoubleFormat = &llvm::APFloat::IEEEdouble();
     }
 
     // PPC64 supports atomics up to 8 bytes.
     MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;
   }
 
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::CharPtrBuiltinVaList;
   }
 
   // PPC64 Linux-specific ABI options.

clang/test/Layout/aix-Wpacked-expecting-diagnostics.cpp

+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -Wpacked \
+// RUN:     -fdump-record-layouts -fsyntax-only -verify -x c++ < %s | \
+// RUN:   FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -Wpacked \
+// RUN:     -fdump-record-layouts -fsyntax-only -verify -x c++ < %s | \
+// RUN:   FileCheck %s
+
+struct A {
+  double d;
+};
+
+struct B {
+  char x[8];
+};
+
+struct [[gnu::packed]] C : B, A { // expected-warning{{packed attribute is unnecessary for 'C'}}
+  char x alignas(4)[8];
+} ;
+
+int b = sizeof(C);
+
+// CHECK:               0 | struct C
+// CHECK-NEXT:          0 |   struct B (base)
+// CHECK-NEXT:          0 |     char [8] x
+// CHECK-NEXT:          8 |   struct A (base)
+// CHECK-NEXT:          8 |     double d
+// CHECK-NEXT:         16 |   char [8] x
+// CHECK-NEXT:            | [sizeof=24, dsize=24, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=24, nvalign=4, preferrednvalign=4]

clang/test/Layout/aix-Wpacked-no-diagnostics.cpp

+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -Wpacked \
+// RUN:     -fdump-record-layouts -fsyntax-only -verify -x c++ < %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -Wpacked \
+// RUN:     -fdump-record-layouts -fsyntax-only -verify -x c++ < %s
+
+// expected-no-diagnostics
+
+struct [[gnu::packed]] Q {
+  double x [[gnu::aligned(4)]];
+};
+
+struct QQ : Q { char x; };
+
+int a = sizeof(QQ);

clang/test/Layout/aix-double-struct-member.cpp

+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only -x c++ %s | \
+// RUN:   FileCheck %s
+
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc64-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only -x c++ %s | \
+// RUN:   FileCheck %s
+
+namespace test1 {
+// Test the class layout when having a double which is/is not the first struct
+// member.
+struct D {
+  double d1;
+  int i1;
+};
+
+struct DoubleFirst {
+  struct D d2;
+  int i2;
+};
+
+struct IntFirst {
+  int i3;
+  struct D d3;
+};
+
+int a = sizeof(DoubleFirst);
+int b = sizeof(IntFirst);
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::D
+// CHECK-NEXT:         0 |   double d1
+// CHECK-NEXT:         8 |   int i1
+// CHECK-NEXT:           | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT:           |  nvsize=16, nvalign=4, preferrednvalign=8]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::DoubleFirst
+// CHECK-NEXT:         0 |   struct test1::D d2
+// CHECK-NEXT:         0 |     double d1
+// CHECK-NEXT:         8 |     int i1
+// CHECK-NEXT:        16 |   int i2
+// CHECK-NEXT:           | [sizeof=24, dsize=24, align=4, preferredalign=8,
+// CHECK-NEXT:           |  nvsize=24, nvalign=4, preferrednvalign=8]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test1::IntFirst
+// CHECK-NEXT:         0 |   int i3
+// CHECK-NEXT:         4 |   struct test1::D d3
+// CHECK-NEXT:         4 |     double d1
+// CHECK-NEXT:        12 |     int i1
+// CHECK-NEXT:           | [sizeof=20, dsize=20, align=4, preferredalign=4,
+// CHECK-NEXT:           |  nvsize=20, nvalign=4, preferrednvalign=4]
+} // namespace test1
+
+namespace test2 {
+// Test the class layout when having a zero-sized bitfield followed by double.
+struct Double {
+  int : 0;
+  double d;
+};
+
+int a = sizeof(Double);
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:         0 | struct test2::Double
+// CHECK-NEXT:       0:- |   int
+// CHECK-NEXT:         0 |   double d
+// CHECK-NEXT:           | [sizeof=8, dsize=8, align=4, preferredalign=4,
+// CHECK-NEXT:           |  nvsize=8, nvalign=4, preferrednvalign=4]
+} // namespace test2
+
+namespace test3 {
+// Test the class layout when having a double member in union.
+union A {
+  int b;
+  double d;
+};
+
+struct UnionStruct {
+  union A a;
+  int i;
+};
+
+int a = sizeof(UnionStruct);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | union test3::A
+// CHECK-NEXT:          0 |   int b
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test3::UnionStruct
+// CHECK-NEXT:          0 |   union test3::A a
+// CHECK-NEXT:          0 |     int b
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |   int i
+// CHECK-NEXT:            | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=16, nvalign=4, preferrednvalign=8]
+
+} // namespace test3
+
+namespace test4 {
+// Test the class layout when having multiple base classes.
+struct A {
+  int a;
+};
+
+struct B {
+  double d;
+};
+
+class S : A, B {
+};
+
+int a = sizeof(S);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test4::A
+// CHECK-NEXT:          0 |   int a
+// CHECK-NEXT:            | [sizeof=4, dsize=4, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=4, nvalign=4, preferrednvalign=4]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test4::B
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | class test4::S
+// CHECK-NEXT:          0 |   struct test4::A (base)
+// CHECK-NEXT:          0 |     int a
+// CHECK-NEXT:          4 |   struct test4::B (base)
+// CHECK-NEXT:          4 |     double d
+// CHECK-NEXT:            | [sizeof=12, dsize=12, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=12, nvalign=4, preferrednvalign=4]
+} // namespace test4
+
+namespace test5 {
+struct Empty {
+};
+
+struct EmptyDer : Empty {
+  double d;
+};
+
+struct NonEmpty {
+  int i;
+};
+
+struct NonEmptyDer : NonEmpty {
+  double d;
+};
+
+int a = sizeof(EmptyDer);
+int b = sizeof(NonEmptyDer);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::Empty (empty)
+// CHECK-NEXT:            | [sizeof=1, dsize=1, align=1, preferredalign=1,
+// CHECK-NEXT:            |  nvsize=1, nvalign=1, preferrednvalign=1]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::EmptyDer
+// CHECK-NEXT:          0 |   struct test5::Empty (base) (empty)
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::NonEmpty
+// CHECK-NEXT:          0 |   int i
+// CHECK-NEXT:            | [sizeof=4, dsize=4, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=4, nvalign=4, preferrednvalign=4]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test5::NonEmptyDer
+// CHECK-NEXT:          0 |   struct test5::NonEmpty (base)
+// CHECK-NEXT:          0 |     int i
+// CHECK-NEXT:          4 |   double d
+// CHECK-NEXT:            | [sizeof=12, dsize=12, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=12, nvalign=4, preferrednvalign=4]
+} // namespace test5
+
+namespace test6 {
+struct A {
+  struct B {
+    double d[3];
+  } b;
+};
+
+int a = sizeof(A);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test6::A::B
+// CHECK-NEXT:          0 |   double [3] d
+// CHECK-NEXT:            | [sizeof=24, dsize=24, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=24, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test6::A
+// CHECK-NEXT:          0 |   struct test6::A::B b
+// CHECK-NEXT:          0 |     double [3] d
+// CHECK-NEXT:            | [sizeof=24, dsize=24, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=24, nvalign=4, preferrednvalign=8]
+
+} // namespace test6
+
+namespace test7 {
+struct A {
+  struct B {
+    long double _Complex d[3];
+  } b;
+};
+
+int a = sizeof(A);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test7::A::B
+// CHECK-NEXT:          0 |   _Complex long double [3] d
+// CHECK-NEXT:            | [sizeof=48, dsize=48, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=48, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test7::A
+// CHECK-NEXT:          0 |   struct test7::A::B b
+// CHECK-NEXT:          0 |     _Complex long double [3] d
+// CHECK-NEXT:            | [sizeof=48, dsize=48, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=48, nvalign=4, preferrednvalign=8]
+
+} // namespace test7
+
+namespace test8 {
+struct Emp {};
+
+struct Y : Emp {
+  double d;
+};
+
+struct Z : Emp {
+  Y y;
+};
+
+int a = sizeof(Z);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test8::Emp (empty)
+// CHECK-NEXT:            | [sizeof=1, dsize=1, align=1, preferredalign=1,
+// CHECK-NEXT:            |  nvsize=1, nvalign=1, preferrednvalign=1]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test8::Y
+// CHECK-NEXT:          0 |   struct test8::Emp (base) (empty)
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test8::Z
+// CHECK-NEXT:          0 |   struct test8::Emp (base) (empty)
+// CHECK-NEXT:          8 |   struct test8::Y y
+// CHECK-NEXT:          8 |     struct test8::Emp (base) (empty)
+// CHECK-NEXT:          8 |     double d
+// CHECK-NEXT:            | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=16, nvalign=4, preferrednvalign=8]
+
+} // namespace test8
+
+namespace test9 {
+// Test the class layout when having a zero-extent array in a base class, which
+// renders the base class not empty.
+struct A { char zea[0]; };
+
+struct B : A { double d; };
+
+struct C { double d; };
+struct D : A, C { char x; };
+
+int a = sizeof(B);
+int b = sizeof(D);
+
+// CHECK:               0 | struct test9::B
+// CHECK-NEXT:          0 |   struct test9::A (base)
+// CHECK-NEXT:          0 |     char [0] zea
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=4]
+
+// CHECK:               0 | struct test9::D
+// CHECK-NEXT:          0 |   struct test9::A (base)
+// CHECK-NEXT:          0 |     char [0] zea
+// CHECK-NEXT:          0 |   struct test9::C (base)
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |   char x
+// CHECK-NEXT:            | [sizeof=12, dsize=9, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=9, nvalign=4, preferrednvalign=4]
+
+} // namespace test9
+
+namespace test10 {
+struct A { double x; };
+struct B : A {} b;
+
+int a = sizeof(B);
+
+// CHECK:               0 | struct test10::B
+// CHECK-NEXT:          0 |   struct test10::A (base)
+// CHECK-NEXT:          0 |     double x
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+} // namespace test10
+
+namespace test11 {
+// Test how #pragma pack and align attribute interacts with AIX `power`
+// alignment rules.
+struct A {
+  char a;
+  double __attribute__((aligned(16))) d;
+  int i;
+};
+
+struct B {
+  double __attribute__((aligned(4))) d1;
+  char a;
+  double d2;
+};
+
+#pragma pack(2)
+struct C {
+  int i;
+  short j;
+  double k;
+};
+
+#pragma pack(2)
+struct D {
+  double d;
+  short j;
+  int i;
+};
+
+#pragma pack(8)
+struct E {
+  double __attribute__((aligned(4))) d;
+  short s;
+};
+
+#pragma pack(4)
+struct F : public D {
+  double d;
+};
+
+#pragma pack(2)
+struct G : public E {
+  int i;
+};
+
+int a = sizeof(A);
+int b = sizeof(B);
+int c = sizeof(C);
+int d = sizeof(D);
+int e = sizeof(E);
+int f = sizeof(F);
+int g = sizeof(G);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::A
+// CHECK-NEXT:          0 |   char a
+// CHECK-NEXT:         16 |   double d
+// CHECK-NEXT:         24 |   int i
+// CHECK-NEXT:            | [sizeof=32, dsize=32, align=16, preferredalign=16,
+// CHECK-NEXT:            |  nvsize=32, nvalign=16, preferrednvalign=16]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::B
+// CHECK-NEXT:          0 |   double d1
+// CHECK-NEXT:          8 |   char a
+// CHECK-NEXT:         12 |   double d2
+// CHECK-NEXT:            | [sizeof=24, dsize=24, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=24, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::C
+// CHECK-NEXT:          0 |   int i
+// CHECK-NEXT:          4 |   short j
+// CHECK-NEXT:          6 |   double k
+// CHECK-NEXT:            | [sizeof=14, dsize=14, align=2, preferredalign=2,
+// CHECK-NEXT:            |  nvsize=14, nvalign=2, preferrednvalign=2]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::D
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:          8 |   short j
+// CHECK-NEXT:         10 |   int i
+// CHECK-NEXT:            | [sizeof=14, dsize=14, align=2, preferredalign=2,
+// CHECK-NEXT:            |  nvsize=14, nvalign=2, preferrednvalign=2]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::E
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:          8 |   short s
+// CHECK-NEXT:            | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=16, nvalign=4, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::F
+// CHECK-NEXT:          0 |   struct test11::D (base)
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |     short j
+// CHECK-NEXT:         10 |     int i
+// CHECK-NEXT:         16 |   double d
+// CHECK-NEXT:            | [sizeof=24, dsize=24, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=24, nvalign=4, preferrednvalign=4]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct test11::G
+// CHECK-NEXT:          0 |   struct test11::E (base)
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |     short s
+// CHECK-NEXT:         16 |   int i
+// CHECK-NEXT:            | [sizeof=20, dsize=20, align=2, preferredalign=2,
+// CHECK-NEXT:            |  nvsize=20, nvalign=2, preferrednvalign=2]
+
+} // namespace test11

clang/test/Layout/aix-no-unique-address-with-double.cpp

+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only %s | \
+// RUN:   FileCheck %s
+
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc64-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only %s | \
+// RUN:   FileCheck %s
+
+struct Empty {};
+
+struct A {
+  double d;
+};
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct Empty (empty)
+// CHECK-NEXT:            | [sizeof=1, dsize=1, align=1, preferredalign=1,
+// CHECK-NEXT:            |  nvsize=1, nvalign=1, preferrednvalign=1]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct A
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=8]
+
+struct B {
+  ~B();
+
+  Empty emp;
+  A a;
+  char c;
+};
+
+struct B1 {
+  [[no_unique_address]] B b;
+  char ext[7];
+};
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct B
+// CHECK-NEXT:          0 |   struct Empty emp (empty)
+// CHECK-NEXT:          4 |   struct A a
+// CHECK-NEXT:          4 |     double d
+// CHECK-NEXT:         12 |   char c
+// CHECK-NEXT:            | [sizeof=16, dsize=13, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=13, nvalign=4, preferrednvalign=4]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct B1
+// CHECK-NEXT:          0 |   struct B b
+// CHECK-NEXT:          0 |     struct Empty emp (empty)
+// CHECK-NEXT:          4 |     struct A a
+// CHECK-NEXT:          4 |       double d
+// CHECK-NEXT:         12 |     char c
+// CHECK-NEXT:         13 |   char [7] ext
+// CHECK-NEXT:            | [sizeof=20, dsize=20, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=20, nvalign=4, preferrednvalign=4]
+
+struct C {
+  ~C();
+
+  [[no_unique_address]] Empty emp;
+  A a;
+  char c;
+};
+
+struct C1 {
+  [[no_unique_address]] C c;
+  char ext[7];
+};
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct C
+// CHECK-NEXT:          0 |   struct Empty emp (empty)
+// CHECK-NEXT:          0 |   struct A a
+// CHECK-NEXT:          0 |     double d
+// CHECK-NEXT:          8 |   char c
+// CHECK-NEXT:            | [sizeof=16, dsize=9, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=9, nvalign=4, preferrednvalign=8]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct C1
+// CHECK-NEXT:          0 |   struct C c
+// CHECK-NEXT:          0 |     struct Empty emp (empty)
+// CHECK-NEXT:          0 |     struct A a
+// CHECK-NEXT:          0 |       double d
+// CHECK-NEXT:          8 |     char c
+// CHECK-NEXT:          9 |   char [7] ext
+// CHECK-NEXT:            | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT:            |  nvsize=16, nvalign=4, preferrednvalign=8]
+
+struct D {
+  ~D();
+
+  [[no_unique_address]] char notEmp;
+  A a;
+  char c;
+};
+
+struct D1 {
+  [[no_unique_address]] D d;
+  char ext[7];
+};
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct D
+// CHECK-NEXT:          0 |   char notEmp
+// CHECK-NEXT:          4 |   struct A a
+// CHECK-NEXT:          4 |     double d
+// CHECK-NEXT:         12 |   char c
+// CHECK-NEXT:            | [sizeof=16, dsize=13, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=13, nvalign=4, preferrednvalign=4]
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct D1
+// CHECK-NEXT:          0 |   struct D d
+// CHECK-NEXT:          0 |     char notEmp
+// CHECK-NEXT:          4 |     struct A a
+// CHECK-NEXT:          4 |       double d
+// CHECK-NEXT:         12 |     char c
+// CHECK-NEXT:         13 |   char [7] ext
+// CHECK-NEXT:            | [sizeof=20, dsize=20, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=20, nvalign=4, preferrednvalign=4]
+
+struct E {
+  [[no_unique_address]] Empty emp;
+  int : 0;
+  double d;
+};
+
+// CHECK:     *** Dumping AST Record Layout
+// CHECK-NEXT:          0 | struct E
+// CHECK-NEXT:          0 |   struct Empty emp (empty)
+// CHECK-NEXT:        0:- |   int
+// CHECK-NEXT:          0 |   double d
+// CHECK-NEXT:            | [sizeof=8, dsize=8, align=4, preferredalign=4,
+// CHECK-NEXT:            |  nvsize=8, nvalign=4, preferrednvalign=4]
+
+int a = sizeof(Empty);
+int b = sizeof(A);
+int c = sizeof(B1);
+int d = sizeof(C1);
+int e = sizeof(D1);
+int f = sizeof(E);

clang/test/Layout/aix-pack-attr-on-base.cpp

+// RUN: %clang_cc1 -S -emit-llvm -triple powerpc-ibm-aix-xcoff -x c++ < %s | \
+// RUN:   FileCheck %s
+
+// RUN: %clang_cc1 -S -emit-llvm -triple powerpc64-ibm-aix-xcoff -x c++ < %s | \
+// RUN:   FileCheck %s
+
+struct A {
+  char x;
+};
+
+struct B {
+  int x;
+};
+
+struct __attribute__((__packed__)) C : A, B {} c;
+
+int s = sizeof(c);
+
+// CHECK: @c = global %struct.C zeroinitializer, align 1
+// CHECK: @s = global i32 5

clang/test/Layout/aix-power-alignment-typedef.cpp

+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -S -emit-llvm \
+// RUN:     -fdump-record-layouts -x c++ < %s | \
+// RUN:   FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -S -emit-llvm \
+// RUN:     -fdump-record-layouts -x c++ < %s | \
+// RUN:   FileCheck %s
+
+namespace test1 {
+struct C {
+  double x;
+} c;
+typedef struct C __attribute__((__aligned__(2))) CC;
+
+CC cc;
+
+// CHECK-DAG: @_ZN5test12ccE = global %"struct.test1::C" zeroinitializer, align 2
+
+} //namespace test1
+
+namespace test2 {
+typedef double __attribute__((__aligned__(2))) Dbl;
+struct A {
+  Dbl x;
+} a;
+
+int b = sizeof(A);
+
+// CHECK:          0 | struct test2::A
+// CHECK-NEXT:     0 |   test2::Dbl x
+// CHECK-NEXT:       | [sizeof=8, dsize=8, align=2, preferredalign=2,
+// CHECK-NEXT:       |  nvsize=8, nvalign=2, preferrednvalign=2]
+
+} // namespace test2
+
+namespace test3 {
+typedef double Dbl __attribute__((__aligned__(2)));
+typedef Dbl DblArr[];
+
+union U {
+  DblArr da;
+  char x;
+} u;
+
+int x = sizeof(U);
+
+// CHECK:          0 | union test3::U
+// CHECK-NEXT:     0 |   test3::DblArr da
+// CHECK-NEXT:     0 |   char x
+// CHECK-NEXT:       | [sizeof=2, dsize=2, align=2, preferredalign=2,
+// CHECK-NEXT:       |  nvsize=2, nvalign=2, preferrednvalign=2]
+
+} // namespace test3

clang/test/Layout/aix-virtual-function-and-base-with-double.cpp

+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,CHECK32 %s
+
+// RUN: %clang_cc1 -emit-llvm-only -triple powerpc64-ibm-aix-xcoff \
+// RUN:     -fdump-record-layouts -fsyntax-only %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,CHECK64 %s
+
+namespace test1 {
+struct A {
+  double d1;
+  virtual void boo() {}
+};
+
+struct B {
+  double d2;
+  A a;
+};
+
+struct C : public A {
+  double d3;
+};
+
+int i = sizeof(B);
+int j = sizeof(C);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test1::A
+// CHECK-NEXT:            0 |   (A vtable pointer)
+// CHECK32-NEXT:          4 |   double d1
+// CHECK32-NEXT:            | [sizeof=12, dsize=12, align=4, preferredalign=4,
+// CHECK32-NEXT:            |  nvsize=12, nvalign=4, preferrednvalign=4]
+// CHECK64-NEXT:          8 |   double d1
+// CHECK64-NEXT:            | [sizeof=16, dsize=16, align=8, preferredalign=8,
+// CHECK64-NEXT:            |  nvsize=16, nvalign=8, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test1::B
+// CHECK-NEXT:            0 |   double d2
+// CHECK-NEXT:            8 |   struct test1::A a
+// CHECK-NEXT:            8 |     (A vtable pointer)
+// CHECK32-NEXT:         12 |     double d1
+// CHECK32-NEXT:            | [sizeof=24, dsize=20, align=4, preferredalign=8,
+// CHECK32-NEXT:            |  nvsize=20, nvalign=4, preferrednvalign=8]
+// CHECK64-NEXT:         16 |     double d1
+// CHECK64-NEXT:            | [sizeof=24, dsize=24, align=8, preferredalign=8,
+// CHECK64-NEXT:            |  nvsize=24, nvalign=8, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test1::C
+// CHECK-NEXT:            0 |   struct test1::A (primary base)
+// CHECK-NEXT:            0 |     (A vtable pointer)
+// CHECK32-NEXT:          4 |     double d1
+// CHECK32-NEXT:         12 |   double d3
+// CHECK32-NEXT:            | [sizeof=20, dsize=20, align=4, preferredalign=4,
+// CHECK32-NEXT:            |  nvsize=20, nvalign=4, preferrednvalign=4]
+// CHECK64-NEXT:          8 |     double d1
+// CHECK64-NEXT:         16 |   double d3
+// CHECK64-NEXT:            | [sizeof=24, dsize=24, align=8, preferredalign=8,
+// CHECK64-NEXT:            |  nvsize=24, nvalign=8, preferrednvalign=8]
+
+} // namespace test1
+
+namespace test2 {
+struct A {
+  long long l1;
+};
+
+struct B : public virtual A {
+  double d2;
+};
+
+#pragma pack(2)
+struct C : public virtual A {
+  double __attribute__((aligned(4))) d3;
+};
+
+int i = sizeof(B);
+int j = sizeof(C);
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test2::A
+// CHECK-NEXT:            0 |   long long l1
+// CHECK-NEXT:              | [sizeof=8, dsize=8, align=8, preferredalign=8,
+// CHECK-NEXT:              |  nvsize=8, nvalign=8, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test2::B
+// CHECK-NEXT:            0 |   (B vtable pointer)
+// CHECK32-NEXT:          4 |   double d2
+// CHECK64-NEXT:          8 |   double d2
+// CHECK-NEXT:           16 |   struct test2::A (virtual base)
+// CHECK-NEXT:           16 |     long long l1
+// CHECK-NEXT:              | [sizeof=24, dsize=24, align=8, preferredalign=8,
+// CHECK32-NEXT:            |  nvsize=12, nvalign=4, preferrednvalign=4]
+// CHECK64-NEXT:            |  nvsize=16, nvalign=8, preferrednvalign=8]
+
+// CHECK:      *** Dumping AST Record Layout
+// CHECK-NEXT:            0 | struct test2::C
+// CHECK-NEXT:            0 |   (C vtable pointer)
+// CHECK32-NEXT:          4 |   double d3
+// CHECK32-NEXT:         12 |   struct test2::A (virtual base)
+// CHECK32-NEXT:         12 |     long long l1
+// CHECK32-NEXT:            | [sizeof=20, dsize=20, align=2, preferredalign=2,
+// CHECK32-NEXT:            |  nvsize=12, nvalign=2, preferrednvalign=2]
+// CHECK64-NEXT:          8 |   double d3
+// CHECK64-NEXT:         16 |   struct test2::A (virtual base)
+// CHECK64-NEXT:         16 |     long long l1
+// CHECK64-NEXT:            | [sizeof=24, dsize=24, align=2, preferredalign=2,
+// CHECK64-NEXT:            |  nvsize=16, nvalign=2, preferrednvalign=2]
+
+} // namespace test2