C99 partial re-initialization behavior (DR-253)

[ygao]

Summary

Hi all,

Based on previous discussion on the mailing list, clang currently lacks support
for C99 partial re-initialization behavior:
Reference: http://lists.cs.uiuc.edu/pipermail/cfe-dev/2013-April/029188.html
Reference: http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_253.htm

I am proposing the following patch hopefully to fix this problem.

Given the following code snippet,

struct P1 { char x[6]; };
struct LP1 { struct P1 p1; };

struct LP1 l = { .p1 = { "foo" }, .p1.x[2] = 'x' };
// this example is adapted from the example for "struct fred x[]" in DR-253;
// currently clang produces in l: { "\0\0x" },
//   whereas gcc 4.8 produces { "fox" };
// with this fix, clang will also produce: { "fox" };

The idea is that upon seeing the second initializer, we will add a member to
the InitListExpr corresponding to ".p1" to hold the expression "{ "foo" }",
whereas one child field of the InitListExpr will hold "x". We keep this
structure till the CodeGen phase where we evaluate "{ "foo" }" and recursively
pass down its (evaluated) values as needed to the child fields of ".p1". The
recursion will stop at the child fields which are initialized with a
brace-enclosed list (if they exist).

From the Sema phase till the codeGen phase, the initializers for "l.p1" are
stored in two separate places: the new PrevInitExpr member of the top-level
InitListExpr, and the various child elements of the InitListExpr. This makes
it more complicated to do synatic/semantic checking of the initializer list.
This proposed patch does not cover all the semantic checking cases, but a
subsequent patch might be needed to do all the semantic checking on the new
PrevInitExpr member.

In the case where a string literal appears in place of "{ "foo" }", clang
evaluates it to a llvm::ConstantDataArray, which is not very easy to pass down
its components down to the child fields. In this proposal, I implemented a
method to build a llvm::ConstantArray out of a given ConstantDataArray. This is
the only part of the patch implemented in the llvm backend and will need to be
committed before the other parts. Or, maybe there are better ways to solve this?

Could someone take a look at the patch?

• Gao

[rsmith]

The right way to deal with this is to expand initializers like { "foo" } to { 'f', 'o', 'o' } in the structured form of the InitListExpr if a designator tries to replace an element of the list.

llvm/tools/clang/include/clang/AST/Expr.h

3784 ↗

(On Diff #14906)

This is a huge and unacceptable layering violation. It is not OK for the AST to refer to IR-level constructs.

[ygao]

Hi Richard,
A lot of thanks for your feedback. I revised the patch based on your feedback.
More advice would be appreciated,

• Gao

[ygao]

A gentle ping.

[ygao]

ping

[ygao]

Ping.
Re-based patch to trunk r222712.

[ygao]

A post-Thanksgiving ping.

[ygao]

Another ping.

[ygao]

Yet another ping

[ygao]

ping.
Happy Christmas!

[• Quuxplusone]

Commented on a test. The functional change is way out of my league.
Also consider adding a "three-pass" test case similar to

struct B { int b1; int c; int b2; };
struct A { int a1; struct B b; int a2; };
struct A a = { 1, { 2, 3, 4 }, 5,
             .b = { 6, 7, 8 },
                .b.c = 9
};
struct A expected = { 1, { 6, 9, 8 }, 5 };
assert(!memcmp(a, expected));

test/CodeGen/partial-reinitialization1.c

55–62

You don't need any of these lines, right?
(If you ran this test on triples other than x64, you might want something like this, but it would have to be in lieu of the CHECK on line 67, not just defining an unused macro up here.)

[probinson]

Hi Gao,
I just noticed you had llvm-commits on the cc list, but as this is a
clang-only patch it seems that would be unnecessary. And it might cause
email to be mis-filed, for example I have mine set up to put all email
sent to both llvm-commits and cfe-commits to ignore the cfe-commits
recipient.
--paulr

[ygao]

Hey Arthur,
You are right about the test file. I do not need the macro definitions. I think I copied those lines
from another test. I added the three-pass test you suggested.
Thanks for reviewing the patch!

I also removed llvm-commits from the subscriber list,

[rsmith]

Sorry for the delay; I've been thinking about this problem for a while and I think I now have a reasonable design for it. Consider a case like this:

struct Q { int a, b, c; };
Q *f();
void g() {
  struct A { Q q; } a = { *f(), .q.b = 3 };
}

Here, we can't model the initialization of a.q as a partial merge (because we have no way to represent initializing a.q.a and a.q.c from the same call to *f(), but initializing a.q.b from 3). I don't like the design of extending InitListExpr with a PrevInitExpr because it makes all users of that type need to cope with a weird special case; I'd prefer a more uniform representation.

So here's what I propose: add a DesignatedInitUpdateExpr that represents updating an initializer with another initializer by way of a designated initializer. This would have three members: the "base" initializer, the "update" initializer representing an initializer for a subobject of the "base", and a list of designators referring to the field of the base that is updated.

The evaluation semantics for a DIUE would be to first initialize the object using the "base" initializer, and then re-initialize the designated subobject using the "update" initializer. If the updated subobject is of a type that needs destruction, we'll need to pick between either running the destructor for the updated subobject, or rejecting designated initializations that would re-initialize a subobject with a non-trivial destructor (we may also need to take care if the updated subobject is a union member, because the initialized subobject might be a different one).

So in the above case, the initializer for a would be:

• An InitListExpr for a, with type A
• The init for field 0 (q) is a DesignatedInitUpdateExpr, with type Q and designator b
• The "base" for the DIUE is the expression *f()
• The "update" for the DIUE is the expression 3

We could still use something like your partialMergeFrom functionality where possible, and only create DesignatedInitUpdateExprs when necessary, but there are implications here: if an initializer has side-effects DIUE can preserve those side-effects even if the initializer is completely overridden, whereas partialMergeFrom will always lose the side-effects. The C standard allows either choice here, but I think we should be as consistent as we reasonably can. I suggest that we use partialMergeFrom wherever possible, and put the DIUE at the 'lowest' place possible within the initializer, so that we (attempt to) discard side-effects from all expressions that don't contribute to the final result. If we discard a side-effecting initializer in this way, we should issue a warning.

One other thing: partialMergeFrom should be a static function in SemaInit.cpp, not a member of InitListExpr (and maybe it might make more sense to integrate its functionality directly into InitListChecker). It's too high-level to belong on the AST.

[ygao]

Hi Richard,
Here is an updated patch based on your suggestion earlier. We discussed this
briefly during the social, but for the record, I tried several different representations
for the vector of "updater" expressions and settled on using an InitListExpr for now.
Using an InitListExpr avoids having to decode a DesignatedInitExpr in
the CodeGen phase, and also allows merging multiple DesignatedInitExpr into
a common data structure, which then allows better diagnostics. The problem of
having to leave "holes" in an InitListExpr (to account for fields that are initialized by
the "base" expression and not to be overwritten by zeros) is solved by inserting a
new type of NoInitExpr as placeholders into these "holes."

There are two new functions in lib/AST/StmtProfile.cpp which I had to add in
order to build clang, but for which I am having trouble writing coverage tests. I
left a FIXME note there for now.

Feedback and advice are greatly appreciated,

• Gao

[ygao]

Updating the patch to trunk r232975.
A very gentle ping?

[ygao]

A gentle ping.

[ygao]

A more real ping.

[ygao]

I ping, therefore I am.

[rsmith]

This is looking really good. I'm not entirely sure that NoInitExpr is necessary -- we could define a null Expr* within the update list of a DesignatedInitUpdateExpr as meaning "perform no initialization" instead -- but we can look at removing it after this patch lands.

include/clang/AST/Expr.h

4313

Put the * on the right, please, and capitalize as lBraceLoc / rBraceLoc.

lib/AST/Expr.cpp

2779

I would think this should be:

return Base->isConstantInitializer(...) && Update->isConstantInitializer(...)

4001

Given that we store the brace locations on the Updater, do we need to also store them inside DesignatedInitUpdateExpr?

4006–4016

This will give a range of Base start to Updater end if there's no LBraceLoc / RBraceLoc, which is a source range that can contain things unrelated to the update. Updater's end loc is always the same as RBraceLoc anyway, so should this instead return getBase()->getLocEnd()?

lib/AST/StmtProfile.cpp

716–724

To test these, put a DesignatedInitUpdateExpr in the signature of a function template, and declare it twice:

template<typename T> void f(decltype(T((char[4]){"foo", [2] = 'x'}))) {} // expected-note {{previous}}
template<typename T> void f(decltype(T((char[4]){"foo", [2] = 'r'}))) {} // ok
template<typename T> void f(decltype(T((char[4]){"boo", [2] = 'x'}))) {} // ok
template<typename T> void f(decltype(T((char[4]){"foo", [2] = 'x'}))) {} // expected-error {{redefinition}}

lib/CodeGen/CGExprCXX.cpp

955–972

This seems like a good idea, but not obviously related to this change. Can you split this out into a separate patch?

lib/Sema/SemaInit.cpp

653–664

If we're using NoInit here, we shouldn't PerformEmptyInit, because that might fail and in any case will wastefully produce an AST node that we don't want.

2187–2204

I would prefer to see this case handled by teaching AST/ExprConstant to evaluate DesignatedInitUpdateExpr and always using the code below, rather than trying to convert an existing initializer into an InitListExpr.

2829–2831

Is it useful to warn on overriding an array filler with an explicit value? This case seems unlikely to be a bug.

test/CodeGen/partial-reinitialization2.c

2

Executable/interpreted tests aren't acceptable here. Please check for specific IR being generated instead.

[ygao]

Thanks for reviewing this.

lib/AST/Expr.cpp

2779

This function may get called in the middle of the initialization process, at which point the updater still contains unfilled "holes". I do not really want to call isConstantInitialzier() on such an updater, therefore the assertion here. Hmm, since I am so confident that Base will not be a constant initializer, maybe I can even just set culprit to Base without running isConstantInitializer() on it?

4001

I think you are right. I can get the brace locations from the updater without storing a duplicate copy.

4006–4016

Updater's end loc is always the same as RBraceLoc anyway.

Are you sure? If the RBraceLoc is not valid, then the updater's RBraceLoc is not valid either, so updater->getLocEnd() should return the end location of the last non-null initializer.

[rsmith]

lib/AST/Expr.cpp

2779

I don't think we should be calling this during initialization at all. If we really want to pull apart, say, a StringLiteral into an InitListExpr of CharacterLiterals (and I'm not convinced that we do, for source fidelity reasons), we should just do that directly in SemaInit without regard to whether the initializer supports constant emission.

4006–4016

OK, good point. Nonetheless, the range from getLocStart() to getLocEnd() should cover a contiguous range of code covering only this expression, and if the brace locations are invalid, then we'll use Base->getLocStart() to Updater->getLocEnd(), which might cover other stuff.

[ygao]

lib/AST/StmtProfile.cpp

716–724

Looks like StmtProfiler::VisitInitListExpr() only works on the syntactic form, and the syntac form
does not contain any DesignatedInitUpdateExpr. I can leave these two methods unimplemented.
I will add your test cases.

lib/CodeGen/CGExprCXX.cpp

952–953

There is a problem here. If I make a clean checkout newer than r234097 (I used r236298) and
comment out these three lines above, clang would crash with the test case below, even though
they are supposed to be just an optimization. r234095 is the last revision which works without
this assertion.

$ clang -S -std=c++11 -emit-llvm -o - test.cpp
Assertion `!PointeeType || PointeeType == getSourceElementType()' failed.

// test.cpp
int n;
struct T { int a; };
void *r = new T[n][3]{ { 1, 2, 3 }, { 4, 5, 6 } };

I am not sure if this is a real bug since I had to modify the compiler source, but If I make the rest of
the changes in this patch but leave out the new optimization below, I would be introducing the
same assertion. Maybe I can add this optimization first before the rest of the patch.

lib/Sema/SemaInit.cpp

2187–2204

You probably meant lib/CodeGen/CGExprConstant.cpp? I can move the logic of
partialMergeFrom() from Sema into CodeGen. The only down side seems to be that the
diagnostic becomes (arguably) less accurate. To illustrate, say we have the following two cases.

struct S {
  char L[6];
};

struct S
Case1[] = {
  "foo",          // expected-note{{previous initialization is here}}
  [0].L[4] = 'x'  // expected-warning{{subobject initialization overrides initialization of other fields}}
};

struct S
Case2[] = {
  { { 'f', 'o', 'o' } },
  [0].L[4] = 'x' // no-warning
};

If I break down a string literal into a tree of char literal initializers during semantic analysis, the compiler will treat the two cases the same and issue no warning for either. If I do not break down the string literal and delay till code gen, then in the Sema phase, the compiler only
sees that Case1[0].L in its entirety was initialized with a string literal, and so it will warn that Case1[0].L[4] is being reinitialized. It's a minor issue in my
opinion, but thought I should point it out during review.

[ygao]

Updated the patch to address previous review comments.

[ygao]

A gentle ping?

[ygao]

Ping.

Also add David Blaikie. He might have some insight on whether lib/CodeGen/CGExprCXX.cpp#952-953 indicates any actual problem.
http://reviews.llvm.org/D5789?id=22530#inline-76127

[ygao]

Ah, sorry I did not provide more context before pulling you in.

The assertion is related to GetElementPointer and I thought you may have worked on this recently;
also there was no assertion before your r234096+r234097. I am not sure if the assertion indicates
a real problem here because I had to modify the compiler source to show the problem. You probably
know better.

[Step#1] apply the following patch: it comments out an optimization.

Index: llvm/tools/clang/lib/CodeGen/CGExprCXX.cpp

• llvm/tools/clang/lib/CodeGen/CGExprCXX.cpp (revision 238351)

+++ llvm/tools/clang/lib/CodeGen/CGExprCXX.cpp (working copy)
@@ -953,10 +953,12 @@

assert(getContext().hasSameUnqualifiedType(ElementType, Init->getType()) &&
       "got wrong type of element to initialize");

+#if 0

// If we have an empty initializer list, we can usually use memset.
if (auto *ILE = dyn_cast<InitListExpr>(Init))
  if (ILE->getNumInits() == 0 && TryMemsetInitialization())
    return;

+#endif

// Create the loop blocks.
llvm::BasicBlock *EntryBB = Builder.GetInsertBlock();

[Step#2] Compile the following test case:

// test.cpp
int n;
struct T { int a; };
void *r = new T[n][3]{ { 1, 2, 3 }, { 4, 5, 6 } };

$ build/Debug+Asserts/bin/clang -S -std=c++11 -emit-llvm -o - test.cpp
clang: llvm/include/llvm/IR/Instructions.h:842: static llvm::GetElementPtrInst* llvm::GetElementPtrInst::Create(llvm::Type*, llvm::Value*, llvm::ArrayRef<llvm::Value*>, const llvm::Twine&, llvm::Instruction*): Assertion `PointeeType == cast<PointerType>(Ptr->getType()->getScalarType())->getElementType()' failed.
0 clang 0x00000000046113de llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 44
1 clang 0x00000000046116f3
2 clang 0x00000000046101f4
3 libpthread.so.0 0x00007fedccedf340
4 libc.so.6 0x00007fedcc11bf79 gsignal + 57
5 libc.so.6 0x00007fedcc11f388 abort + 328
6 libc.so.6 0x00007fedcc114e36
7 libc.so.6 0x00007fedcc114ee2
8 clang 0x00000000017077ff
9 clang 0x00000000017078af
10 clang 0x0000000001764c8c
11 clang 0x00000000018f5662 clang::CodeGen::CodeGenFunction::EmitNewArrayInitializer(clang::CXXNewExpr const*, clang::QualType, llvm::Type*, llvm::Value*, llvm::Value*, llvm::Value*) + 3100
12 clang 0x00000000018f57a6
13 clang 0x00000000018f6d60 clang::CodeGen::CodeGenFunction::EmitCXXNewExpr(clang::CXXNewExpr const*) + 1950
14 clang 0x000000000190489c
15 clang 0x00000000019154af
16 clang 0x00000000019038d2
17 clang 0x00000000019095ba
18 clang 0x0000000001917257
19 clang 0x00000000019156d7
20 clang 0x00000000019038d2
21 clang 0x00000000019141b2 clang::CodeGen::CodeGenFunction::EmitScalarExpr(clang::Expr const*, bool) + 128
22 clang 0x00000000018b2e75 clang::CodeGen::CodeGenFunction::EmitScalarInit(clang::Expr const*, clang::ValueDecl const*, clang::CodeGen::LValue, bool) + 99
23 clang 0x00000000018bb9b2
24 clang 0x00000000018bc0b7 clang::CodeGen::CodeGenFunction::EmitCXXGlobalVarDeclInit(clang::VarDecl const&, llvm::Constant*, bool) + 437
25 clang 0x00000000018bdd1f clang::CodeGen::CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function*, clang::VarDecl const*, llvm::GlobalVariable*, bool) + 501
26 clang 0x00000000018bcda1 clang::CodeGen::CodeGenModule::EmitCXXGlobalVarDeclInitFunc(clang::VarDecl const*, llvm::GlobalVariable*, bool) + 615
27 clang 0x0000000001774193 clang::CodeGen::CodeGenModule::EmitGlobalVarDefinition(clang::VarDecl const*) + 2291
28 clang 0x000000000177216f clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) + 531
29 clang 0x00000000017719ca clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) + 796
30 clang 0x00000000017792a2 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) + 438
31 clang 0x00000000016c6215
32 clang 0x00000000016aabb6
33 clang 0x00000000019ac057 clang::ParseAST(clang::Sema&, bool, bool) + 553
34 clang 0x00000000013a8fe2 clang::ASTFrontendAction::ExecuteAction() + 322
35 clang 0x00000000016ad592 clang::CodeGenAction::ExecuteAction() + 1486
36 clang 0x00000000013a8ac1 clang::FrontendAction::Execute() + 139
37 clang 0x000000000136c902 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 772
38 clang 0x000000000132dadb clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 993
39 clang 0x0000000001318d68 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 770
40 clang 0x0000000001327500
41 clang 0x0000000001327ae7 main + 1074
42 libc.so.6 0x00007fedcc106ec5 __libc_start_main + 245
43 clang 0x0000000001317469
Stack dump:
0. Program arguments: build/Debug+Asserts/bin/clang -cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -disable-free -main-file-name test.cpp -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -target-linker-version 2.24 -dwarf-column-info -coverage-file /tmp/- -resource-dir build/Debug+Asserts/bin/../lib/clang/3.7.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/x86_64-linux-gnu/c++/4.8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/x86_64-linux-gnu/c++/4.8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/backward -internal-isystem /usr/local/include -internal-isystem build/Debug+Asserts/bin/../lib/clang/3.7.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 205 -mstackrealign -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -o - -x c++ test.cpp

1. <eof> parser at end of file
2. test.cpp:4:7: LLVM IR generation of declaration 'r'
3. test.cpp:4:7: Generating code for declaration 'r'

clang: error: unable to execute command: Aborted (core dumped)
clang: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 3.7.0 (trunk 238351)
Target: x86_64-unknown-linux-gnu
Thread model: posix
clang: note: diagnostic msg: PLEASE submit a bug report to http://llvm.org/bugs/ and include the crash backtrace, preprocessed source, and associated run script.
clang: note: diagnostic msg:

---

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang: note: diagnostic msg: /tmp/test-d13456.cpp
clang: note: diagnostic msg: /tmp/test-d13456.sh
clang: note: diagnostic msg:

[rsmith]

I think it might be possible to get rid of the NoInitExpr here, but let's not worry about that for now. Just a couple of comments and then we can go ahead with this.

lib/CodeGen/CGExprConstant.cpp

865 ↗

(On Diff #24911)

This case can actually happen; you can return nullptr (for now) if it does.

1125 ↗

(On Diff #24911)

There is no guarantee that the layout of Base matches that of the InitListExpr; you should check that here and bail out in that case.

[ygao]

Thanks. I updated the patch addressing the two small comments, and also rebased to r239192.

[rsmith]

+ Bail out if the type of the ConstantStruct does not have the same
layout
+ as the type of the InitListExpr.
+ if (CGM.getTypes().ConvertType(Field->getType()) != EltInit->getType())
+ return false;

I don't think that's quite enough; even if all the types of the
ConstantStruct match the types of the fields, the fields might be at
different offsets (due to an alignment attribute). This could happen if the
original initializer initializes one member of a union and the update
expression initializes a different member. Use getStructLayout on the
DataLayout object to find the offset of the fields within the
ConstantStruct and compare them to the offset from the ASTRecordLayout
object.

[ygao]

Addressing review feedback.

[rsmith]

Please update your llvm_unreachable("Not implemented");s to say why the code is unreachable ("should not exist in syntactic form of initializer" or similar). Other than that, let's go ahead with this change.

Thanks for your extreme patience!

[Eugene.Zelenko]

Committed in rL239446.

include/clang/AST/DataRecursiveASTVisitor.h

 DEF_TRAVERSE_STMT(CXXThrowExpr, {})
 DEF_TRAVERSE_STMT(UserDefinedLiteral, {})
 DEF_TRAVERSE_STMT(DesignatedInitExpr, {})
+DEF_TRAVERSE_STMT(DesignatedInitUpdateExpr, {})
 DEF_TRAVERSE_STMT(ExtVectorElementExpr, {})
 DEF_TRAVERSE_STMT(GNUNullExpr, {})
 DEF_TRAVERSE_STMT(ImplicitValueInitExpr, {})
+DEF_TRAVERSE_STMT(NoInitExpr, {})
 DEF_TRAVERSE_STMT(ObjCBoolLiteralExpr, {})
 DEF_TRAVERSE_STMT(ObjCEncodeExpr, {
   if (TypeSourceInfo *TInfo = S->getEncodedTypeSourceInfo())

include/clang/AST/Expr.h

   }
 };
 
+/// \brief Represents a place-holder for an object not to be initialized by
+/// anything.
+///
+/// This only makes sense when it appears as part of an updater of a
+/// DesignatedInitUpdateExpr (see below). The base expression of a DIUE
+/// initializes a big object, and the NoInitExpr's mark the spots within the
+/// big object not to be overwritten by the updater.
+///
+/// \see DesignatedInitUpdateExpr
+class NoInitExpr : public Expr {
+public:
+  explicit NoInitExpr(QualType ty)
+    : Expr(NoInitExprClass, ty, VK_RValue, OK_Ordinary,
+           false, false, ty->isInstantiationDependentType(), false) { }
+
+  explicit NoInitExpr(EmptyShell Empty)
+    : Expr(NoInitExprClass, Empty) { }
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == NoInitExprClass;
+  }
+
+  SourceLocation getLocStart() const LLVM_READONLY { return SourceLocation(); }
+  SourceLocation getLocEnd() const LLVM_READONLY { return SourceLocation(); }
+
+  // Iterators
+  child_range children() { return child_range(); }
+};
+
+// In cases like:
+//   struct Q { int a, b, c; };
+//   Q *getQ();
+//   void foo() {
+//     struct A { Q q; } a = { *getQ(), .q.b = 3 };
+//   }
+//
+// We will have an InitListExpr for a, with type A, and then a
+// DesignatedInitUpdateExpr for "a.q" with type Q. The "base" for this DIUE
+// is the call expression *getQ(); the "updater" for the DIUE is ".q.b = 3"
+//
+class DesignatedInitUpdateExpr : public Expr {
+  // BaseAndUpdaterExprs[0] is the base expression;
+  // BaseAndUpdaterExprs[1] is an InitListExpr overwriting part of the base.
+  Stmt *BaseAndUpdaterExprs[2];
+  SourceLocation LBraceLoc, RBraceLoc;
+
+public:
+  DesignatedInitUpdateExpr(const ASTContext &C, SourceLocation lbraceloc,
+                           Expr* baseExprs, SourceLocation rbraceloc);
+
+  explicit DesignatedInitUpdateExpr(EmptyShell Empty)
+    : Expr(DesignatedInitUpdateExprClass, Empty) { }
+
+  SourceLocation getLocStart() const LLVM_READONLY;
+  SourceLocation getLocEnd() const LLVM_READONLY;
+
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == DesignatedInitUpdateExprClass;
+  }
+
+  SourceLocation getLBraceLoc() const { return LBraceLoc; }
+  void setLBraceLoc(SourceLocation Loc) { LBraceLoc = Loc; }
+  SourceLocation getRBraceLoc() const { return RBraceLoc; }
+  void setRBraceLoc(SourceLocation Loc) { RBraceLoc = Loc; }
+
+  Expr *getBase() const { return cast<Expr>(BaseAndUpdaterExprs[0]); }
+  void setBase(Expr *Base) { BaseAndUpdaterExprs[0] = Base; }
+
+  InitListExpr *getUpdater() const {
+    return cast<InitListExpr>(BaseAndUpdaterExprs[1]);
+  }
+  void setUpdater(Expr *Updater) { BaseAndUpdaterExprs[1] = Updater; }
+
+  // Iterators
+  // children = the base and the updater
+  child_range children() {
+    return child_range(&BaseAndUpdaterExprs[0], &BaseAndUpdaterExprs[0] + 2);
+  }
+};
+
 /// \brief Represents an implicitly-generated value initialization of
 /// an object of a given type.
 ///

include/clang/AST/RecursiveASTVisitor.h

 DEF_TRAVERSE_STMT(CXXThrowExpr, {})
 DEF_TRAVERSE_STMT(UserDefinedLiteral, {})
 DEF_TRAVERSE_STMT(DesignatedInitExpr, {})
+DEF_TRAVERSE_STMT(DesignatedInitUpdateExpr, {})
 DEF_TRAVERSE_STMT(ExtVectorElementExpr, {})
 DEF_TRAVERSE_STMT(GNUNullExpr, {})
 DEF_TRAVERSE_STMT(ImplicitValueInitExpr, {})
+DEF_TRAVERSE_STMT(NoInitExpr, {})
 DEF_TRAVERSE_STMT(ObjCBoolLiteralExpr, {})
 DEF_TRAVERSE_STMT(ObjCEncodeExpr, {
   if (TypeSourceInfo *TInfo = S->getEncodedTypeSourceInfo())

include/clang/Basic/StmtNodes.td

 def ExtVectorElementExpr : DStmt<Expr>;
 def InitListExpr : DStmt<Expr>;
 def DesignatedInitExpr : DStmt<Expr>;
+def DesignatedInitUpdateExpr : DStmt<Expr>;
 def ImplicitValueInitExpr : DStmt<Expr>;
+def NoInitExpr : DStmt<Expr>;
 def ParenListExpr : DStmt<Expr>;
 def VAArgExpr : DStmt<Expr>;
 def GenericSelectionExpr : DStmt<Expr>;

include/clang/Serialization/ASTBitCodes.h

       EXPR_INIT_LIST,
       /// \brief A DesignatedInitExpr record.
       EXPR_DESIGNATED_INIT,
+      /// \brief A DesignatedInitUpdateExpr record.
+      EXPR_DESIGNATED_INIT_UPDATE,
       /// \brief An ImplicitValueInitExpr record.
       EXPR_IMPLICIT_VALUE_INIT,
+      /// \brief An NoInitExpr record.
+      EXPR_NO_INIT,
       /// \brief A VAArgExpr record.
       EXPR_VA_ARG,
       /// \brief An AddrLabelExpr record.

lib/AST/Expr.cpp

     const Expr *Exp = cast<CompoundLiteralExpr>(this)->getInitializer();
     return Exp->isConstantInitializer(Ctx, false, Culprit);
   }
+  case DesignatedInitUpdateExprClass: {
+    const DesignatedInitUpdateExpr *DIUE = cast<DesignatedInitUpdateExpr>(this);
+    if (!DIUE->getBase()->isConstantInitializer(Ctx, false, Culprit))
+      return false;
+    assert(false && "DIUE->getBase() should not be a constant expression");
+    break;
+  }
   case InitListExprClass: {
     const InitListExpr *ILE = cast<InitListExpr>(this);
     if (ILE->getType()->isArrayType()) {

     break;
   }
   case ImplicitValueInitExprClass:
+  case NoInitExprClass:
     return true;
   case ParenExprClass:
     return cast<ParenExpr>(this)->getSubExpr()

   case UnaryExprOrTypeTraitExprClass:
   case AddrLabelExprClass:
   case GNUNullExprClass:
+  case NoInitExprClass:
   case CXXBoolLiteralExprClass:
   case CXXNullPtrLiteralExprClass:
   case CXXThisExprClass:

   case CompoundLiteralExprClass:
   case ExtVectorElementExprClass:
   case DesignatedInitExprClass:
+  case DesignatedInitUpdateExprClass:
   case ParenListExprClass:
   case CXXPseudoDestructorExprClass:
   case CXXStdInitializerListExprClass:

   NumDesignators = NumDesignators - 1 + NumNewDesignators;
 }
 
+DesignatedInitUpdateExpr::DesignatedInitUpdateExpr(const ASTContext &C,
+    SourceLocation lbraceloc, Expr *baseExpr, SourceLocation rbraceloc)
+  : Expr(DesignatedInitUpdateExprClass, baseExpr->getType(), VK_RValue,
+         OK_Ordinary, false, false, false, false),
+    LBraceLoc(lbraceloc), RBraceLoc(rbraceloc) {
+  BaseAndUpdaterExprs[0] = baseExpr;
+
+  InitListExpr *ILE = new (C) InitListExpr(C, lbraceloc, None, rbraceloc);
+  ILE->setType(baseExpr->getType());
+  BaseAndUpdaterExprs[1] = ILE;
+}
+
+SourceLocation DesignatedInitUpdateExpr::getLocStart() const {
+  if (LBraceLoc.isValid())
+    return LBraceLoc;
+  return getBase()->getLocStart();
+}
+
+SourceLocation DesignatedInitUpdateExpr::getLocEnd() const {
+  if (RBraceLoc.isValid())
+    return RBraceLoc;
+  return getUpdater()->getLocEnd();
+}
+
 ParenListExpr::ParenListExpr(const ASTContext& C, SourceLocation lparenloc,
                              ArrayRef<Expr*> exprs,
                              SourceLocation rparenloc)

lib/AST/ExprClassification.cpp

   case Expr::ObjCIndirectCopyRestoreExprClass:
   case Expr::AtomicExprClass:
   case Expr::CXXFoldExprClass:
+  case Expr::NoInitExprClass:
+  case Expr::DesignatedInitUpdateExprClass:
     return Cl::CL_PRValue;
 
     // Next come the complicated cases.

lib/AST/ExprConstant.cpp

   case Expr::CompoundLiteralExprClass:
   case Expr::ExtVectorElementExprClass:
   case Expr::DesignatedInitExprClass:
+  case Expr::NoInitExprClass:
+  case Expr::DesignatedInitUpdateExprClass:
   case Expr::ImplicitValueInitExprClass:
   case Expr::ParenListExprClass:
   case Expr::VAArgExprClass:

lib/AST/ItaniumMangle.cpp

   // These all can only appear in local or variable-initialization
   // contexts and so should never appear in a mangling.
   case Expr::AddrLabelExprClass:
+  case Expr::DesignatedInitUpdateExprClass:
   case Expr::ImplicitValueInitExprClass:
+  case Expr::NoInitExprClass:
   case Expr::ParenListExprClass:
   case Expr::LambdaExprClass:
   case Expr::MSPropertyRefExprClass:

lib/AST/StmtPrinter.cpp

   PrintExpr(Node->getInit());
 }
 
+void StmtPrinter::VisitDesignatedInitUpdateExpr(
+    DesignatedInitUpdateExpr *Node) {
+  OS << "{";
+  OS << "/*base*/";
+  PrintExpr(Node->getBase());
+  OS << ", ";
+
+  OS << "/*updater*/";
+  PrintExpr(Node->getUpdater());
+  OS << "}";
+}
+
+void StmtPrinter::VisitNoInitExpr(NoInitExpr *Node) {
+  OS << "/*no init*/";
+}
+
 void StmtPrinter::VisitImplicitValueInitExpr(ImplicitValueInitExpr *Node) {
   if (Policy.LangOpts.CPlusPlus) {
     OS << "/*implicit*/";

lib/AST/StmtProfile.cpp

   }
 }
 
+// FIXME: how to test these functions?
+void StmtProfiler::VisitDesignatedInitUpdateExpr(
+    const DesignatedInitUpdateExpr *S) {
+  llvm_unreachable("Not implemented");
+}
+
+void StmtProfiler::VisitNoInitExpr(const NoInitExpr *S) {
+  llvm_unreachable("Not implemented");
+}
+
 void StmtProfiler::VisitImplicitValueInitExpr(const ImplicitValueInitExpr *S) {
   VisitExpr(S);
 }

lib/CodeGen/CGExprAgg.cpp

     EmitAggLoadOfLValue(E);
   }
 
+  void VisitDesignatedInitUpdateExpr(DesignatedInitUpdateExpr *E);
   void VisitAbstractConditionalOperator(const AbstractConditionalOperator *CO);
   void VisitChooseExpr(const ChooseExpr *CE);
   void VisitInitListExpr(InitListExpr *E);
   void VisitImplicitValueInitExpr(ImplicitValueInitExpr *E);
+  void VisitNoInitExpr(NoInitExpr *E) { } // Do nothing.
   void VisitCXXDefaultArgExpr(CXXDefaultArgExpr *DAE) {
     Visit(DAE->getExpr());
   }

     return;
   } else if (isa<ImplicitValueInitExpr>(E) || isa<CXXScalarValueInitExpr>(E)) {
     return EmitNullInitializationToLValue(LV);
+  } else if (isa<NoInitExpr>(E)) {
+    // Do nothing.
+    return;
   } else if (type->isReferenceType()) {
     RValue RV = CGF.EmitReferenceBindingToExpr(E);
     return CGF.EmitStoreThroughLValue(RV, LV);

     cleanupDominator->eraseFromParent();
 }
 
+void AggExprEmitter::VisitDesignatedInitUpdateExpr(DesignatedInitUpdateExpr *E) {
+  AggValueSlot Dest = EnsureSlot(E->getType());
+
+  LValue DestLV = CGF.MakeAddrLValue(Dest.getAddr(), E->getType(),
+                                     Dest.getAlignment());
+  EmitInitializationToLValue(E->getBase(), DestLV);
+  VisitInitListExpr(E->getUpdater());
+}
+
 //===----------------------------------------------------------------------===//
 //                        Entry Points into this File
 //===----------------------------------------------------------------------===//

lib/CodeGen/CGExprCXX.cpp

     if (ILE->getNumInits() == 0 && TryMemsetInitialization())
       return;
 
+  // If we have a struct whose every field is value-initialized, we can
+  // usually use memset.
+  if (auto *ILE = dyn_cast<InitListExpr>(Init)) {
+    if (const RecordType *RType = ILE->getType()->getAs<RecordType>()) {
+      if (RType->getDecl()->isStruct()) {
+        unsigned NumFields = 0;
+        for (auto *Field : RType->getDecl()->fields())
+          if (!Field->isUnnamedBitfield())
+            ++NumFields;
+        if (ILE->getNumInits() == NumFields)
+          for (unsigned i = 0, e = ILE->getNumInits(); i != e; ++i)
+            if (!isa<ImplicitValueInitExpr>(ILE->getInit(i)))
+              --NumFields;
+        if (ILE->getNumInits() == NumFields && TryMemsetInitialization())
+          return;
+      }
+    }
+  }
+
   // Create the loop blocks.
   llvm::BasicBlock *EntryBB = Builder.GetInsertBlock();
   llvm::BasicBlock *LoopBB = createBasicBlock("new.loop");

lib/Sema/SemaExceptionSpec.cpp

   case Expr::CXXReinterpretCastExprClass:
   case Expr::CXXStdInitializerListExprClass:
   case Expr::DesignatedInitExprClass:
+  case Expr::DesignatedInitUpdateExprClass:
   case Expr::ExprWithCleanupsClass:
   case Expr::ExtVectorElementExprClass:
   case Expr::InitListExprClass:

   case Expr::ImaginaryLiteralClass:
   case Expr::ImplicitValueInitExprClass:
   case Expr::IntegerLiteralClass:
+  case Expr::NoInitExprClass:
   case Expr::ObjCEncodeExprClass:
   case Expr::ObjCStringLiteralClass:
   case Expr::ObjCBoolLiteralExprClass:

lib/Sema/SemaInit.cpp

                                            QualType CurrentObjectType,
                                            InitListExpr *StructuredList,
                                            unsigned StructuredIndex,
-                                           SourceRange InitRange);
+                                           SourceRange InitRange,
+                                           bool IsFullyOverwritten = false);
   void UpdateStructuredListElement(InitListExpr *StructuredList,
                                    unsigned &StructuredIndex,
                                    Expr *expr);

                                      SourceLocation Loc,
                                      const InitializedEntity &Entity,
                                      bool VerifyOnly);
+
+  // Explanation on the "FillWithNoInit" mode:
+  //
+  // Assume we have the following definitions (Case#1):
+  // struct P { char x[6][6]; } xp = { .x[1] = "bar" };
+  // struct PP { struct P lp; } l = { .lp = xp, .lp.x[1][2] = 'f' };
+  //
+  // l.lp.x[1][0..1] should not be filled with implicit initializers because the
+  // "base" initializer "xp" will provide values for them; l.lp.x[1] will be "baf".
+  //
+  // But if we have (Case#2):
+  // struct PP l = { .lp = xp, .lp.x[1] = { [2] = 'f' } };
+  //
+  // l.lp.x[1][0..1] are implicitly initialized and do not use values from the
+  // "base" initializer; l.lp.x[1] will be "\0\0f\0\0\0".
+  //
+  // To distinguish Case#1 from Case#2, and also to avoid leaving many "holes"
+  // in the InitListExpr, the "holes" in Case#1 are filled not with empty
+  // initializers but with a special "NoInitExpr" place holders, which tells the
+  // CodeGen not to generate any initializers for these parts.
   void FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
                                const InitializedEntity &ParentEntity,
-                               InitListExpr *ILE, bool &RequiresSecondPass);
+                               InitListExpr *ILE, bool &RequiresSecondPass,
+                               bool FillWithNoInit = false);
   void FillInEmptyInitializations(const InitializedEntity &Entity,
-                                  InitListExpr *ILE, bool &RequiresSecondPass);
+                                  InitListExpr *ILE, bool &RequiresSecondPass,
+                                  bool FillWithNoInit = false);
   bool CheckFlexibleArrayInit(const InitializedEntity &Entity,
                               Expr *InitExpr, FieldDecl *Field,
                               bool TopLevelObject);

 void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
                                         const InitializedEntity &ParentEntity,
                                               InitListExpr *ILE,
-                                              bool &RequiresSecondPass) {
+                                              bool &RequiresSecondPass,
+                                              bool FillWithNoInit) {
   SourceLocation Loc = ILE->getLocEnd();
   unsigned NumInits = ILE->getNumInits();
   InitializedEntity MemberEntity
     = InitializedEntity::InitializeMember(Field, &ParentEntity);
+
+  if (const RecordType *RType = ILE->getType()->getAs<RecordType>())
+    if (!RType->getDecl()->isUnion())
+      assert(Init < NumInits && "This ILE should have been expanded");
+
   if (Init >= NumInits || !ILE->getInit(Init)) {
+    if (FillWithNoInit) {
+      Expr *Filler = new (SemaRef.Context) NoInitExpr(Field->getType());
+      if (Init < NumInits)
+        ILE->setInit(Init, Filler);
+      else
+        ILE->updateInit(SemaRef.Context, Init, Filler);
+      return;
+    }
     // C++1y [dcl.init.aggr]p7:
     //   If there are fewer initializer-clauses in the list than there are
     //   members in the aggregate, then each member not explicitly initialized

   } else if (InitListExpr *InnerILE
                = dyn_cast<InitListExpr>(ILE->getInit(Init)))
     FillInEmptyInitializations(MemberEntity, InnerILE,
-                               RequiresSecondPass);
+                               RequiresSecondPass, FillWithNoInit);
+  else if (DesignatedInitUpdateExpr *InnerDIUE
+               = dyn_cast<DesignatedInitUpdateExpr>(ILE->getInit(Init)))
+    FillInEmptyInitializations(MemberEntity, InnerDIUE->getUpdater(),
+                               RequiresSecondPass, /*FillWithNoInit =*/ true);
 }
 
 /// Recursively replaces NULL values within the given initializer list

 void
 InitListChecker::FillInEmptyInitializations(const InitializedEntity &Entity,
                                             InitListExpr *ILE,
-                                            bool &RequiresSecondPass) {
+                                            bool &RequiresSecondPass,
+                                            bool FillWithNoInit) {
   assert((ILE->getType() != SemaRef.Context.VoidTy) &&
          "Should not have void type");
 

     const RecordDecl *RDecl = RType->getDecl();
     if (RDecl->isUnion() && ILE->getInitializedFieldInUnion())
       FillInEmptyInitForField(0, ILE->getInitializedFieldInUnion(),
-                              Entity, ILE, RequiresSecondPass);
+                              Entity, ILE, RequiresSecondPass, FillWithNoInit);
     else if (RDecl->isUnion() && isa<CXXRecordDecl>(RDecl) &&
              cast<CXXRecordDecl>(RDecl)->hasInClassInitializer()) {
       for (auto *Field : RDecl->fields()) {
         if (Field->hasInClassInitializer()) {
-          FillInEmptyInitForField(0, Field, Entity, ILE, RequiresSecondPass);
+          FillInEmptyInitForField(0, Field, Entity, ILE, RequiresSecondPass,
+                                  FillWithNoInit);
           break;
         }
       }
     } else {
+      // The fields beyond ILE->getNumInits() are default initialized, so in
+      // order to leave them uninitialized, the ILE is expanded and the extra
+      // fields are then filled with NoInitExpr.
+      unsigned NumFields = 0;
+      for (auto *Field : RDecl->fields())
+        if (!Field->isUnnamedBitfield())
+          ++NumFields;
+      if (ILE->getNumInits() < NumFields)
+        ILE->resizeInits(SemaRef.Context, NumFields);
+
       unsigned Init = 0;
       for (auto *Field : RDecl->fields()) {
         if (Field->isUnnamedBitfield())

         if (hadError)
           return;
 
-        FillInEmptyInitForField(Init, Field, Entity, ILE, RequiresSecondPass);
+        FillInEmptyInitForField(Init, Field, Entity, ILE, RequiresSecondPass,
+                                FillWithNoInit);
         if (hadError)
           return;
 

       ElementEntity.setElementIndex(Init);
 
     Expr *InitExpr = (Init < NumInits ? ILE->getInit(Init) : nullptr);
-    if (!InitExpr && !ILE->hasArrayFiller()) {
+    if (!InitExpr && Init < NumInits && ILE->hasArrayFiller())
+      ILE->setInit(Init, ILE->getArrayFiller());
+    else if (!InitExpr && !ILE->hasArrayFiller()) {
       ExprResult ElementInit = PerformEmptyInit(SemaRef, ILE->getLocEnd(),
                                                 ElementEntity,
                                                 /*VerifyOnly*/false);

         return;
       }
 
+      Expr *Filler = FillWithNoInit ?
+          new (SemaRef.Context) NoInitExpr(ElementType) :
+          ElementInit.getAs<Expr>();
+
       if (hadError) {
         // Do nothing
       } else if (Init < NumInits) {

         // For arrays, just set the expression used for value-initialization
         // of the "holes" in the array.
         if (ElementEntity.getKind() == InitializedEntity::EK_ArrayElement)
-          ILE->setArrayFiller(ElementInit.getAs<Expr>());
+          ILE->setArrayFiller(Filler);
         else
-          ILE->setInit(Init, ElementInit.getAs<Expr>());
+          ILE->setInit(Init, Filler);
       } else {
         // For arrays, just set the expression used for value-initialization
         // of the rest of elements and exit.
         if (ElementEntity.getKind() == InitializedEntity::EK_ArrayElement) {
-          ILE->setArrayFiller(ElementInit.getAs<Expr>());
+          ILE->setArrayFiller(Filler);
           return;
         }
 
-        if (!isa<ImplicitValueInitExpr>(ElementInit.get())) {
+        if (!isa<ImplicitValueInitExpr>(Filler) && !isa<NoInitExpr>(Filler)) {
           // Empty initialization requires a constructor call, so
           // extend the initializer list to include the constructor
           // call and make a note that we'll need to take another pass
           // through the initializer list.
-          ILE->updateInit(SemaRef.Context, Init, ElementInit.getAs<Expr>());
+          ILE->updateInit(SemaRef.Context, Init, Filler);
           RequiresSecondPass = true;
         }
       }
     } else if (InitListExpr *InnerILE
                  = dyn_cast_or_null<InitListExpr>(InitExpr))
-      FillInEmptyInitializations(ElementEntity, InnerILE, RequiresSecondPass);
+      FillInEmptyInitializations(ElementEntity, InnerILE, RequiresSecondPass,
+                                 FillWithNoInit);
+    else if (DesignatedInitUpdateExpr *InnerDIUE
+                 = dyn_cast_or_null<DesignatedInitUpdateExpr>(InitExpr))
+      FillInEmptyInitializations(ElementEntity, InnerDIUE->getUpdater(),
+                                 RequiresSecondPass, /*FillWithNoInit =*/ true);
   }
 }
 

                               StructuredList, StructuredIndex);
 
   if (InitListExpr *SubInitList = dyn_cast<InitListExpr>(expr)) {
-    if (!SemaRef.getLangOpts().CPlusPlus) {
+    if (SubInitList->getNumInits() == 1 &&
+        IsStringInit(SubInitList->getInit(0), ElemType, SemaRef.Context) ==
+        SIF_None) {
+      expr = SubInitList->getInit(0);
+    } else if (!SemaRef.getLangOpts().CPlusPlus) {
       InitListExpr *InnerStructuredList
         = getStructuredSubobjectInit(IList, Index, ElemType,
                                      StructuredList, StructuredIndex,
-                                     SubInitList->getSourceRange());
+                                     SubInitList->getSourceRange(), true);
       CheckExplicitInitList(Entity, SubInitList, ElemType,
                             InnerStructuredList);
+
+      if (!hadError && !VerifyOnly) {
+        bool RequiresSecondPass = false;
+        FillInEmptyInitializations(Entity, InnerStructuredList,
+                                   RequiresSecondPass);
+        if (RequiresSecondPass && !hadError)
+          FillInEmptyInitializations(Entity, InnerStructuredList,
+                                     RequiresSecondPass);
+      }
       ++StructuredIndex;
       ++Index;
       return;

 
 }
 
+static void partialMergeFrom(const ASTContext &C, InitListExpr *TargetExpr,
+                             Expr *BackgroundExpr) {
+  assert(!TargetExpr->hasArrayFiller() && "Filler already exists!");
+
+  BackgroundExpr = BackgroundExpr->IgnoreParenImpCasts();
+  if (CompoundLiteralExpr *CLE =
+        dyn_cast<CompoundLiteralExpr>(BackgroundExpr))
+    BackgroundExpr = CLE->getInitializer()->IgnoreParenImpCasts();
+
+  // A string literal or an obj-c encode expression gets decomposed into
+  // individual characters.
+  if (isa<StringLiteral>(BackgroundExpr) ||
+      isa<ObjCEncodeExpr>(BackgroundExpr)) {
+    const ArrayType *AT = C.getAsArrayType(TargetExpr->getType());
+    assert(AT && "expecting array type");
+
+    QualType CharTy = AT->getElementType();
+    QualType PromotedCharTy = (CharTy->isPromotableIntegerType() ?
+      C.getPromotedIntegerType(CharTy) : CharTy);
+    unsigned CharWidth = C.getTypeSize(PromotedCharTy);
+
+    const StringLiteral *SL = dyn_cast<StringLiteral>(BackgroundExpr);
+    const ObjCEncodeExpr *OEE = dyn_cast<ObjCEncodeExpr>(BackgroundExpr);
+    std::string OEE_Str;
+    if (OEE)
+      C.getObjCEncodingForType(OEE->getEncodedType(), OEE_Str);
+
+    uint64_t StrLen = SL ? SL->getLength() : OEE_Str.size();
+    const llvm::APInt &ArraySize = cast<ConstantArrayType>(AT)->getSize();
+    if (ArraySize.ult(StrLen))
+      StrLen = ArraySize.getZExtValue();
+
+    if (StrLen > TargetExpr->getNumInits())
+      TargetExpr->resizeInits(C, StrLen);
+
+    for (unsigned i = 0; i != StrLen; ++i) {
+      if (TargetExpr->getInit(i))
+        continue;
+
+      llvm::APInt Element(CharWidth, SL ? SL->getCodeUnit(i) : OEE_Str[i]);
+      Expr *ElementExpr = IntegerLiteral::Create(C, Element, PromotedCharTy,
+                                                 BackgroundExpr->getExprLoc());
+      if (CharTy != PromotedCharTy)
+        ElementExpr = ImplicitCastExpr::Create(C, CharTy, CK_IntegralCast,
+                                               ElementExpr, nullptr, VK_RValue);
+      TargetExpr->setInit(i, ElementExpr);
+    }
+
+    if (ArraySize.ugt(StrLen))
+      TargetExpr->setArrayFiller(new (C) ImplicitValueInitExpr(CharTy));
+
+    return;
+  }
+
+  if (isa<ImplicitValueInitExpr>(BackgroundExpr)) {
+    unsigned NumInits = TargetExpr->getNumInits();
+
+    if (const RecordType *RType = TargetExpr->getType()->getAs<RecordType>()) {
+      const RecordDecl *RD = RType->getDecl();
+      unsigned i = 0;
+
+      unsigned NumFields = 0;
+      for (FieldDecl *FD : RD->fields()) {
+        if (FD->isUnnamedBitfield())
+          continue;
+        ++NumFields;
+      }
+      if (NumInits < NumFields)
+        TargetExpr->resizeInits(C, NumFields);
+
+      for (RecordDecl::field_iterator I = RD->field_begin(),E = RD->field_end();
+           I != E; ++I, ++i) {
+        FieldDecl *FD = *I;
+        if (FD->isUnnamedBitfield()) {
+          --i;
+          continue;
+        }
+
+        ImplicitValueInitExpr *EmptyInit =
+          new (C) ImplicitValueInitExpr(FD->getType());
+
+        if (!TargetExpr->getInit(i)) {
+          TargetExpr->setInit(i, EmptyInit);
+          continue;
+        }
+
+        // If this is not an aggregate type, we are done. The current
+        // initializer takes effect; the background initializer is overwritten.
+        Expr *ChildExpr = TargetExpr->getInit(i);
+        if (!ChildExpr->getType()->isAggregateType())
+          continue;
+
+        assert(isa<InitListExpr>(ChildExpr) && "expecting an init list expr");
+
+        InitListExpr *ChildILE = cast<InitListExpr>(ChildExpr);
+        partialMergeFrom(C, ChildILE, EmptyInit);
+
+        // Only look at the first initialization of a union
+        if (TargetExpr->getType()->isUnionType())
+          break;
+      }
+
+      return;
+    }
+
+    QualType ElementType;
+    bool IsArray = false;
+
+    if (const VectorType *VT = TargetExpr->getType()->getAs<VectorType>())
+      ElementType = VT->getElementType();
+    else if (const ArrayType *AT = C.getAsArrayType(TargetExpr->getType())) {
+      ElementType = AT->getElementType();
+      IsArray = true;
+    } else 
+      ElementType = TargetExpr->getType();
+
+    ImplicitValueInitExpr *EmptyInit =
+      new (C) ImplicitValueInitExpr(ElementType);
+
+    if (IsArray)
+      TargetExpr->setArrayFiller(EmptyInit);
+
+    for (unsigned i = 0; i != NumInits; ++i) {
+      if (!TargetExpr->getInit(i) && !IsArray)
+        TargetExpr->setInit(i, EmptyInit);
+
+      // If this is not an aggregate type, we are done. The current
+      // initializer takes effect; the background initializer is overwritten.
+      Expr *ChildExpr = TargetExpr->getInit(i);
+      if (!ChildExpr->getType()->isAggregateType())
+        continue;
+
+      assert(isa<InitListExpr>(ChildExpr) && "expecting an init list expr");
+
+      InitListExpr *ChildILE = cast<InitListExpr>(ChildExpr);
+      partialMergeFrom(C, ChildILE, EmptyInit);
+    }
+
+    return;
+  }
+
+  assert(isa<InitListExpr>(BackgroundExpr) &&
+         "cannot break down background initializer!");
+  InitListExpr *BackgroundILE = cast<InitListExpr>(BackgroundExpr);
+  if (BackgroundILE->getNumInits() > TargetExpr->getNumInits())
+    TargetExpr->resizeInits(C, BackgroundILE->getNumInits());
+
+  for (unsigned i = 0; i != TargetExpr->getNumInits(); ++i) {
+    if (i >= BackgroundILE->getNumInits() || !BackgroundILE->getInit(i))
+      // Nothing to merge from.
+      continue;
+
+    if (!TargetExpr->getInit(i)) {
+      TargetExpr->setInit(i, BackgroundILE->getInit(i));
+      continue;
+    }
+
+    // If this is not an aggregate type, we are done. The current initializer
+    // takes effect; the background initializer is overwritten.
+    Expr *ChildExpr = TargetExpr->getInit(i);
+    if (!ChildExpr->getType()->isAggregateType())
+      continue;
+
+    assert(isa<InitListExpr>(ChildExpr) && "expecting an init list expr");
+
+    InitListExpr *ChildILE = cast<InitListExpr>(ChildExpr);
+    partialMergeFrom(C, ChildILE, BackgroundILE->getInit(i));
+
+    // Only look at the first initialization of a union
+    if (TargetExpr->getType()->isUnionType())
+      break;
+  }
+
+  if (BackgroundILE->hasArrayFiller())
+    TargetExpr->setArrayFiller(BackgroundILE->getArrayFiller());
+}
+
 /// @brief Check the well-formedness of a C99 designated initializer.
 ///
 /// Determines whether the designated initializer @p DIE, which

 
     // Determine the structural initializer list that corresponds to the
     // current subobject.
-    StructuredList = IsFirstDesignator? SyntacticToSemantic.lookup(IList)
-      : getStructuredSubobjectInit(IList, Index, CurrentObjectType,
-                                   StructuredList, StructuredIndex,
-                                   SourceRange(D->getLocStart(),
-                                               DIE->getLocEnd()));
+    if (IsFirstDesignator)
+      StructuredList = SyntacticToSemantic.lookup(IList);
+    else {
+      Expr *ExistingInit = StructuredIndex < StructuredList->getNumInits() ?
+          StructuredList->getInit(StructuredIndex) : nullptr;
+      if (!ExistingInit && StructuredList->hasArrayFiller())
+        ExistingInit = StructuredList->getArrayFiller();
+
+      if (!ExistingInit)
+        StructuredList =
+          getStructuredSubobjectInit(IList, Index, CurrentObjectType,
+                                     StructuredList, StructuredIndex,
+                                     SourceRange(D->getLocStart(),
+                                                 DIE->getLocEnd()));
+      else if (InitListExpr *Result = dyn_cast<InitListExpr>(ExistingInit))
+        StructuredList = Result;
+      else if (ExistingInit->isConstantInitializer(SemaRef.Context, false)) {
+        InitListExpr *Result = new (SemaRef.Context) InitListExpr(
+            SemaRef.Context, D->getLocStart(), None, DIE->getLocEnd());
+
+        QualType ResultType = CurrentObjectType;
+        if (!ResultType->isArrayType())
+          ResultType = ResultType.getNonLValueExprType(SemaRef.Context);
+        Result->setType(ResultType);
+
+        // If we decomposed an aggregate initializer into individual components,
+        // we do not issue diagnostics here; instead we wait till later and
+        // issue diagnostics on each individual component.
+        partialMergeFrom(SemaRef.Context, Result, ExistingInit);
+        ExistingInit = nullptr;
+        StructuredList->updateInit(SemaRef.Context, StructuredIndex, Result);
+        StructuredList = Result;
+      }
+      else {
+        if (DesignatedInitUpdateExpr *E =
+                dyn_cast<DesignatedInitUpdateExpr>(ExistingInit))
+          StructuredList = E->getUpdater();
+        else {
+          DesignatedInitUpdateExpr *DIUE =
+              new (SemaRef.Context) DesignatedInitUpdateExpr(SemaRef.Context,
+                                        D->getLocStart(), ExistingInit,
+                                        DIE->getLocEnd());
+          StructuredList->updateInit(SemaRef.Context, StructuredIndex, DIUE);
+          StructuredList = DIUE->getUpdater();
+        }
+
+        // We are creating an initializer list that initializes the
+        // subobjects of the current object, but there was already an
+        // initialization that completely initialized the current
+        // subobject, e.g., by a compound literal:
+        //
+        // struct X { int a, b; };
+        // struct X xs[] = { [0] = (struct X) { 1, 2 }, [0].b = 3 };
+        //
+        // Here, xs[0].a == 0 and xs[0].b == 3, since the second,
+        // designated initializer re-initializes the whole
+        // subobject [0], overwriting previous initializers.
+        SemaRef.Diag(D->getLocStart(),
+                     diag::warn_subobject_initializer_overrides)
+          << SourceRange(D->getLocStart(), DIE->getLocEnd());
+  
+        // We need to check on source range validity because the previous
+        // initializer does not have to be an explicit initializer. e.g.,
+        //
+        // struct P { int a, b; };
+        // struct PP { struct P p } l = { { .a = 2 }, .p.b = 3 };
+        //
+        // There is an overwrite taking place because the first braced initializer
+        // list "{ .a = 2 }" already provides value for .p.b (which is zero).
+        if (ExistingInit->getSourceRange().isValid())
+          SemaRef.Diag(ExistingInit->getLocStart(),
+                       diag::note_previous_initializer)
+            << /*FIXME:has side effects=*/0
+            << ExistingInit->getSourceRange();
+      }
+    }
     assert(StructuredList && "Expected a structured initializer list");
   }
 

                                             QualType CurrentObjectType,
                                             InitListExpr *StructuredList,
                                             unsigned StructuredIndex,
-                                            SourceRange InitRange) {
+                                            SourceRange InitRange,
+                                            bool IsFullyOverwritten) {
   if (VerifyOnly)
     return nullptr; // No structured list in verification-only mode.
   Expr *ExistingInit = nullptr;

     ExistingInit = StructuredList->getInit(StructuredIndex);
 
   if (InitListExpr *Result = dyn_cast_or_null<InitListExpr>(ExistingInit))
-    return Result;
+    // There might have already been initializers for subobjects of the current
+    // object, but a subsequent initializer list will overwrite the entirety
+    // of the current object. (See DR 253 and C99 6.7.8p21). e.g.,
+    //
+    // struct P { char x[6]; };
+    // struct P l = { .x[2] = 'x', .x = { [0] = 'f' } };
+    //
+    // The first designated initializer is ignored, and l.x is just "f".
+    if (!IsFullyOverwritten)
+      return Result;
 
   if (ExistingInit) {
     // We are creating an initializer list that initializes the

     SemaRef.Diag(expr->getLocStart(),
                   diag::warn_initializer_overrides)
       << expr->getSourceRange();
-    SemaRef.Diag(PrevInit->getLocStart(),
-                  diag::note_previous_initializer)
-      << /*FIXME:has side effects=*/0
-      << PrevInit->getSourceRange();
+
+    // We need to check on source range validity because the previous
+    // initializer does not have to be an explicit initializer.
+    // struct P { int a, b; };
+    // struct PP { struct P p } l = { { .a = 2 }, .p.b = 3 };
+    // There is an overwrite taking place because the first braced initializer
+    // list "{ .a = 2 }' already provides value for .p.b (which is zero).
+    if (PrevInit->getSourceRange().isValid())
+      SemaRef.Diag(PrevInit->getLocStart(),
+                   diag::note_previous_initializer)
+        << /*FIXME:has side effects=*/0
+        << PrevInit->getSourceRange();
   }
+  // It is also possible to overwrite an implicitly initialized array element:
+  // struct S { char L[6]; } var[] = {
+  //   { { 'f', 'o', 'o' } }, // var[0].L[3..6] zero-initialized, and then
+  //   [0].L[4] = 'x' };      // var[0].L[4] was overriden
+  else if (StructuredList->hasArrayFiller()) {
+    SemaRef.Diag(expr->getLocStart(),
+                 diag::warn_initializer_overrides)
+      << expr->getSourceRange();
+  }
 
   ++StructuredIndex;
 }

lib/Sema/TreeTransform.h

                                                 E->usesGNUSyntax(), Init.get());
 }
 
+// Seems that if TransformInitListExpr() only works on the syntactic form of an
+// InitListExpr, then a DesignatedInitUpdateExpr is not encountered.
 template<typename Derived>
 ExprResult
+TreeTransform<Derived>::TransformDesignatedInitUpdateExpr(
+    DesignatedInitUpdateExpr *E) {
+  llvm_unreachable("not implemented");
+  return ExprError();
+}
+
+template<typename Derived>
+ExprResult
+TreeTransform<Derived>::TransformNoInitExpr(
+    NoInitExpr *E) {
+  llvm_unreachable("not implemented");
+  return ExprError();
+}
+
+template<typename Derived>
+ExprResult
 TreeTransform<Derived>::TransformImplicitValueInitExpr(
                                                      ImplicitValueInitExpr *E) {
   TemporaryBase Rebase(*this, E->getLocStart(), DeclarationName());

lib/Serialization/ASTReaderStmt.cpp

                     Designators.data(), Designators.size());
 }
 
+void ASTStmtReader::VisitDesignatedInitUpdateExpr(DesignatedInitUpdateExpr *E) {
+  VisitExpr(E);
+  E->setLBraceLoc(ReadSourceLocation(Record, Idx));
+  E->setRBraceLoc(ReadSourceLocation(Record, Idx));
+  E->setBase(Reader.ReadSubExpr());
+  E->setUpdater(Reader.ReadSubExpr());
+}
+
+void ASTStmtReader::VisitNoInitExpr(NoInitExpr *E) {
+  VisitExpr(E);
+}
+
 void ASTStmtReader::VisitImplicitValueInitExpr(ImplicitValueInitExpr *E) {
   VisitExpr(E);
 }

 
       break;
 
+    case EXPR_DESIGNATED_INIT_UPDATE:
+      S = new (Context) DesignatedInitUpdateExpr(Empty);
+      break;
+
     case EXPR_IMPLICIT_VALUE_INIT:
       S = new (Context) ImplicitValueInitExpr(Empty);
       break;
 
+    case EXPR_NO_INIT:
+      S = new (Context) NoInitExpr(Empty);
+      break;
+
     case EXPR_VA_ARG:
       S = new (Context) VAArgExpr(Empty);
       break;

lib/Serialization/ASTWriter.cpp

   RECORD(EXPR_EXT_VECTOR_ELEMENT);
   RECORD(EXPR_INIT_LIST);
   RECORD(EXPR_DESIGNATED_INIT);
+  RECORD(EXPR_DESIGNATED_INIT_UPDATE);
   RECORD(EXPR_IMPLICIT_VALUE_INIT);
+  RECORD(EXPR_NO_INIT);
   RECORD(EXPR_VA_ARG);
   RECORD(EXPR_ADDR_LABEL);
   RECORD(EXPR_STMT);

lib/Serialization/ASTWriterStmt.cpp

   Code = serialization::EXPR_DESIGNATED_INIT;
 }
 
+void ASTStmtWriter::VisitDesignatedInitUpdateExpr(DesignatedInitUpdateExpr *E) {
+  VisitExpr(E);
+  Writer.AddSourceLocation(E->getLBraceLoc(), Record);
+  Writer.AddSourceLocation(E->getRBraceLoc(), Record);
+  Writer.AddStmt(E->getBase());
+  Writer.AddStmt(E->getUpdater());
+  Code = serialization::EXPR_DESIGNATED_INIT_UPDATE;
+}
+
+void ASTStmtWriter::VisitNoInitExpr(NoInitExpr *E) {
+  VisitExpr(E);
+  Code = serialization::EXPR_NO_INIT;
+}
+
 void ASTStmtWriter::VisitImplicitValueInitExpr(ImplicitValueInitExpr *E) {
   VisitExpr(E);
   Code = serialization::EXPR_IMPLICIT_VALUE_INIT;

lib/StaticAnalyzer/Core/ExprEngine.cpp

 
     // Cases not handled yet; but will handle some day.
     case Stmt::DesignatedInitExprClass:
+    case Stmt::DesignatedInitUpdateExprClass:
     case Stmt::ExtVectorElementExprClass:
     case Stmt::ImaginaryLiteralClass:
     case Stmt::ObjCAtCatchStmtClass:

     case Stmt::CXXBoolLiteralExprClass:
     case Stmt::ObjCBoolLiteralExprClass:
     case Stmt::FloatingLiteralClass:
+    case Stmt::NoInitExprClass:
     case Stmt::SizeOfPackExprClass:
     case Stmt::StringLiteralClass:
     case Stmt::ObjCStringLiteralClass:

test/Analysis/designated-initializer.c

+// RUN: %clang_cc1 -analyze -analyzer-checker=debug.DumpCFG %s 2>&1 \
+// RUN:   | FileCheck %s
+
+struct Q { int a, b, c; };
+union UQ { struct Q q; };
+union UQ getUQ() {
+  union UQ u = { { 1, 2, 3 } };
+  return u;
+}
+
+void test() {
+  struct LUQ { union UQ uq; } var = { getUQ(), .uq.q.a = 100 };
+  struct Q s[] = {
+    [0] = (struct Q){1, 2},
+    [0].c = 3
+  }; 
+}
+
+// CHECK: void test()
+// CHECK: [B1]
+// CHECK:   1: getUQ
+// CHECK:   2: [B1.1] (ImplicitCastExpr, FunctionToPointerDecay, union UQ (*)())
+// CHECK:   3: [B1.2]()
+// CHECK:   4: 100
+// CHECK:   5: /*no init*/
+// CHECK:   6: /*no init*/
+// CHECK:   7: {[B1.4], [B1.5], [B1.6]}
+// CHECK:   8: {[B1.7]}
+// CHECK:   9: {/*base*/[B1.3], /*updater*/[B1.8]}
+// CHECK:  10: {[B1.3], .uq.q.a = [B1.4]}
+// CHECK:  11: struct LUQ var = {getUQ(), .uq.q.a = 100};
+// CHECK:  12: 1
+// CHECK:  13: 2
+// CHECK:  14: 3
+// CHECK:  15: {[B1.12], [B1.13], [B1.14]}
+// CHECK:  16: {[0] = (struct Q){[B1.12], [B1.13]}, [0].c = [B1.14]}
+// CHECK:  17: struct Q s[] = {[0] = (struct Q){1, 2}, [0].c = 3};

test/CodeGen/Inputs/stdio.h

 struct FILE;
+extern int printf(const char *format, ...);
 extern int vfprintf(struct FILE *s, const char *format, __builtin_va_list arg);
 extern int vprintf(const char *format, __builtin_va_list arg);
 

test/CodeGen/partial-reinitialization1.c

+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -isystem %S/Inputs %s -emit-llvm -o - | FileCheck %s
+
+struct P1 {
+    struct Q1 {
+      char a[6];
+      char b[6];
+    } q;
+};
+
+// CHECK: { [6 x i8] c"foo\00\00\00", [6 x i8] c"\00x\00\00\00\00" }
+struct P1 l1 = {
+    (struct Q1){ "foo", "bar" },
+               .q.b = { "boo" },
+               .q.b = { [1] = 'x' }
+};
+
+// CHECK: { [6 x i8] c"foo\00\00\00", [6 x i8] c"bxo\00\00\00" }
+struct P1 l1a = {
+    (struct Q1){ "foo", "bar" },
+               .q.b = { "boo" },
+               .q.b[1] = 'x'
+};
+
+
+struct P2 { char x[6]; };
+
+// CHECK: { [6 x i8] c"n\00\00\00\00\00" }
+struct P2 l2 = {
+  .x = { [1] = 'o' },
+  .x = { [0] = 'n' }
+}; 
+
+struct P3 {
+    struct Q3 {
+      struct R1 {
+         int a, b, c;
+      } r1;
+
+      struct R2 {
+         int d, e, f;
+      } r2;
+    } q;
+};
+
+// CHECK: @l3 = global %struct.P3 { %struct.Q3 { %struct.R1 { i32 1, i32 2, i32 3 }, %struct.R2 { i32 0, i32 10, i32 0 } } }
+struct P3 l3 = {
+  (struct Q3){ { 1, 2, 3 }, { 4, 5, 6 } },
+                    .q.r2 = { 7, 8, 9 },
+                    .q.r2 = { .e = 10 }
+};
+
+// This bit is taken from Sema/wchar.c so we can avoid the wchar.h include.      
+typedef __WCHAR_TYPE__ wchar_t;                                                  
+
+struct P4 {
+    wchar_t x[6];
+};
+
+// CHECK: { [6 x i32] [i32 102, i32 111, i32 120, i32 0, i32 0, i32 0] }
+struct P4 l4 = { { L"foo" }, .x[2] = L'x' };
+
+struct P5 {
+  int x;
+  struct Q5 {
+    int a, b, c;
+  } q;
+  int y;
+};
+
+// A three-pass test
+// CHECK: @l5 = global %struct.P5 { i32 1, %struct.Q5 { i32 6, i32 9, i32 8 }, i32 5 }
+struct P5 l5 = { 1, { 2, 3, 4 }, 5,
+                 .q = { 6, 7, 8 },
+                 .q.b = 9 };

test/CodeGen/partial-reinitialization2.c

+// RUN: %clang_cc1 -isystem %S/Inputs %s -emit-llvm -o - \
+// RUN:   | lli -force-interpreter | FileCheck %s
+
+#include <stdio.h>
+
+struct P1 { char x[6]; } g1 = { "foo" };
+struct LP1 { struct P1 p1; };
+
+struct P2    { int a, b, c; } g2 = { 1, 2, 3 };
+struct LP2   { struct P2 p2; };
+struct LP2P2 { struct P2 p1, p2; };
+union  UP2   { struct P2 p2; };
+
+struct LP3 { struct P1 p1[2]; } g3 = { { "dog" }, { "cat" } };
+struct LLP3 { struct LP3 l3; };
+union ULP3 { struct LP3 l3; };
+
+void test1(void)
+{ // CHECK: fox
+  struct LP1 l = { .p1 = g1, .p1.x[2] = 'x' };
+  int i;
+  for (i = 0; i < 6; i ++)
+    printf("%c", l.p1.x[i]);
+  printf("\n");
+}
+
+void test2(void)
+{ // CHECK: fro
+  struct LP1 l = { .p1 = g1, .p1.x[1] = 'r' };
+  int i;
+  for (i = 0; i < 6; i ++)
+    printf("%c", l.p1.x[i]);
+  printf("\n");
+}
+
+void test3(void)
+{ // CHECK: 1 10 3
+  struct LP2 l = { .p2 = g2, .p2.b = 10 };
+  printf("%d %d %d\n", l.p2.a, l.p2.b, l.p2.c);
+}
+
+#if 0
+// FIXME: with -force-interpreter, the use of struct type here ran into bv21177
+// without -force-interpreter, MCJIT on Windows does not quite work yet.
+struct P2 get235()
+{
+  struct P2 p = { 2, 3, 5 };
+  return p;
+}
+
+struct LP2P2 get456789()
+{
+  struct LP2P2 l = { { 4, 5, 6 }, { 7, 8, 9 } };
+  return l;
+}
+
+union UP2 get123()
+{
+  union UP2 u = { { 1, 2, 3 } };
+  return u;
+}
+#else
+struct P2 my235 = { 2, 3, 5 };
+struct LP2P2 my456789 = { { 4, 5, 6 }, { 7, 8, 9 } };
+union UP2 my123 = { { 1, 2, 3 } };
+#define get235() my235
+#define get456789() my456789
+#define get123() my123
+#endif
+
+void test4(void)
+{ // CHECK: 100 2 3
+  struct LUP2 { union UP2 up; } var = { get123(), .up.p2.a = 100 };
+  printf("%d %d %d\n", var.up.p2.a, var.up.p2.b, var.up.p2.c);
+}
+
+void test5(void)
+{ // CHECK: 0 78 0 0 0 0
+  struct LLP3 var = { .l3 = g3, .l3.p1 = { [0] = g1 }, .l3.p1[1].x[1] = 'x' };
+  int i;
+  for (i = 0; i < 6; i ++)
+    printf("%x ", var.l3.p1[1].x[i]);
+  printf("\n");
+}
+
+void test6(void)
+{ // CHECK: 2 10 5 : 7 8 9
+  struct LLP2P2 { struct LP2P2 lp; } var =  { get456789(),
+                                              .lp.p1 = get235(),
+                                              .lp.p1.b = 10 };
+  printf("%d %d %d : %d %d %d\n",
+          var.lp.p1.a, var.lp.p1.b, var.lp.p1.c,
+          var.lp.p2.a, var.lp.p2.b, var.lp.p2.c);
+}
+
+int main()
+{
+  test1();
+  test2();
+  test3();
+  test4();
+  test5();
+  test6();
+  return 0;
+}

test/PCH/designated-init.c.h

         },
     }
 };
+
+struct P1 {
+    struct Q1 {
+      char a[6];
+      char b[6];
+    } q;
+};
+
+struct P1 l1 = {
+    (struct Q1){ "foo", "bar" },
+               .q.b = { "boo" },
+               .q.b = { [1] = 'x' }
+};
+
+extern struct Q1 *foo();
+static struct P1 test_foo() {
+  struct P1 l = { *foo(),
+                  .q.b = { "boo" },
+                  .q.b = { [1] = 'x' }
+                };
+  return l;
+}

test/Sema/designated-initializers.c

 
 struct point array2[10] = {
   [10].x = 2.0, // expected-error{{array designator index (10) exceeds array bounds (10)}}
-  [4 ... 5].y = 2.0,
-  [4 ... 6] = { .x = 3, .y = 4.0 }
+  [4 ... 5].y = 2.0, // expected-note 2 {{previous initialization is here}}
+  [4 ... 6] = { .x = 3, .y = 4.0 }  // expected-warning 2 {{subobject initialization overrides initialization of other fields within its enclosing subobject}}
 };
 
 struct point array3[10] = {

 void test() {
   struct X xs[] = { 
     [0] = (struct X){1, 2}, // expected-note{{previous initialization is here}}
-    [0].c = 3,  // expected-warning{{subobject initialization overrides initialization of other fields within its enclosing subobject}}
+    [0].c = 3,  // expected-warning{{initializer overrides prior initialization of this subobject}}
     (struct X) {4, 5, 6}, // expected-note{{previous initialization is here}}
-    [1].b = get8(), // expected-warning{{subobject initialization overrides initialization of other fields within its enclosing subobject}}
-    [0].b = 8
+    [1].b = get8(), // expected-warning{{initializer overrides prior initialization of this subobject}}
+    [0].b = 8   // expected-warning{{initializer overrides prior initialization of this subobject}}
   };
 }
 

       .a = 1 // expected-note{{previous initialization is here}}
     } },
   .a = 2, // expected-warning{{initializer overrides prior initialization of this subobject}}
-  .b = 3
+  .b = 3  // expected-warning{{initializer overrides prior initialization of this subobject}}
 };
 struct ds ds1 = { .c = 0 };
 struct ds ds2 = { { {

   int M;
 } overwrite_string2[] = {
     { { "foo" }, 1 },
-    [0].L[4] = 'x' // no-warning
+    [0].L[4] = 'x' // expected-warning{{initializer overrides prior initialization of this subobject}}
   };
+struct overwrite_string_struct
+overwrite_string3[] = {
+  "foo", 1,
+  [0].L[4] = 'x'  // expected-warning{{initializer overrides prior initialization of this subobject}}
+};
+struct overwrite_string_struct
+overwrite_string4[] = {
+  { { 'f', 'o', 'o' }, 1 },
+  [0].L[4] = 'x' // expected-warning{{initializer overrides prior initialization of this subobject}}
+};

tools/libclang/CXCursor.cpp

   case Stmt::CXXUuidofExprClass:
   case Stmt::ChooseExprClass:
   case Stmt::DesignatedInitExprClass:
+  case Stmt::DesignatedInitUpdateExprClass:
   case Stmt::ExprWithCleanupsClass:
   case Stmt::ExpressionTraitExprClass:
   case Stmt::ExtVectorElementExprClass:
   case Stmt::ImplicitCastExprClass:
   case Stmt::ImplicitValueInitExprClass:
+  case Stmt::NoInitExprClass:
   case Stmt::MaterializeTemporaryExprClass:
   case Stmt::ObjCIndirectCopyRestoreExprClass:
   case Stmt::OffsetOfExprClass: