PR44406: Follow behavior of array bound constant folding in more recent versions of GCC.

[rsmith]

Summary

Old GCC used to aggressively fold VLAs to constant-bound arrays at block
scope in GNU mode. That's non-conforming, and more modern versions of
GCC only do this at file scope. Update Clang to do the same.

Also promote the warning for this from off-by-default to on-by-default
in all cases; more recent versions of GCC likewise warn on this by
default.

This is still slightly more permissive than GCC, as pointed out in
PR44406, as we still fold VLAs to constant arrays in structs, but that
seems justifiable given that we don't support VLA-in-struct (and don't
intend to ever support it), but GCC does.

[efriedma]

Also update the documentation? See https://clang.llvm.org/docs/UsersManual.html#differences-between-various-standard-modes .

clang/lib/Sema/SemaDecl.cpp

5939

It's a little surprising to me that you need new code here... was this case getting picked up by the SemaType code?

clang/lib/Sema/SemaType.cpp

2278

We probably want some note to explain why OpenCL is special here... if you can't figure out easily, please leave a FIXME.

[efriedma]

clang/lib/Sema/SemaType.cpp

2278

Oh, I see you posted a separate patch for that.

[rsmith]

clang/lib/Sema/SemaDecl.cpp

5939

Yes, and it previously didn't work outside GNU mode: https://godbolt.org/z/ncqKvo

I suppose that means that it probably isn't important to handle this, but we have a test for the multi-level VLA -> constant array case and it seemed easy enough to make it work.

clang/lib/Sema/SemaType.cpp

2278

For posterity, that's D89520.

[rsmith]

• Update User's Manual to more accurately describe GNU mode and

[rsmith]

• Update User's Manual to more accurately describe GNU mode and

[rsmith]

In D89523#2333939, @efriedma wrote:

Also update the documentation? See https://clang.llvm.org/docs/UsersManual.html#differences-between-various-standard-modes .

Done.

[efriedma]

LGTM

clang/docs/UsersManual.rst

-  The parser recognizes ``asm`` and ``typeof`` as keywords in ``gnu*`` modes;
    the variants ``__asm__`` and ``__typeof__`` are recognized in all modes.
 -  The parser recognizes ``inline`` as a keyword in ``gnu*`` mode, in
    addition to recognizing it in the ``*99`` and later modes for which it is
    part of the ISO C standard. The variant ``__inline__`` is recognized in all
    modes.
 -  The Apple "blocks" extension is recognized by default in ``gnu*`` modes
    on some platforms; it can be enabled in any mode with the ``-fblocks``
    option.
--  Arrays that are VLA's according to the standard, but which can be
-   constant folded by the frontend are treated as fixed size arrays.
-   This occurs for things like "int X[(1, 2)];", which is technically a
-   VLA. ``c*`` modes are strictly compliant and treat these as VLAs.
 
 Differences between ``*89`` and ``*94`` modes:
 
 -  Digraphs are not recognized in c89 mode.
 
 Differences between ``*94`` and ``*99`` modes:
 
 -  The ``*99`` modes default to implementing ``inline`` / ``__inline__``

 ----------------------------------------
 
 -  clang does not support the gcc extension that allows variable-length
    arrays in structures. This is for a few reasons: one, it is tricky to
    implement, two, the extension is completely undocumented, and three,
    the extension appears to be rarely used. Note that clang *does*
    support flexible array members (arrays with a zero or unspecified
    size at the end of a structure).
--  clang does not have an equivalent to gcc's "fold"; this means that
-   clang doesn't accept some constructs gcc might accept in contexts
-   where a constant expression is required, like "x-x" where x is a
-   variable.
+-  GCC accepts many expression forms that are not valid integer constant
+   expressions in bit-field widths, enumerator constants, case labels,
+   and in array bounds at global scope. Clang also accepts additional
+   expression forms in these contexts, but constructs that GCC accepts due to
+   simplifications GCC performs while parsing, such as ``x - x`` (where ``x`` is a
+   variable) will likely never be accepted by Clang.
 -  clang does not support ``__builtin_apply`` and friends; this extension
    is extremely obscure and difficult to implement reliably.
 
 .. _c_ms:
 
 Microsoft extensions
 --------------------
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

 def err_array_star_in_function_definition : Error<
   "variable length array must be bound in function definition">;
 def err_vla_decl_in_file_scope : Error<
   "variable length array declaration not allowed at file scope">;
 def err_vla_decl_has_static_storage : Error<
   "variable length array declaration cannot have 'static' storage duration">;
 def err_vla_decl_has_extern_linkage : Error<
   "variable length array declaration cannot have 'extern' linkage">;
-def ext_vla_folded_to_constant : Extension<
-  "variable length array folded to constant array as an extension">, InGroup<GNUFoldingConstant>;
+def ext_vla_folded_to_constant : ExtWarn<
+  "variable length array folded to constant array as an extension">,
+  InGroup<GNUFoldingConstant>;
 def err_vla_unsupported : Error<
   "variable length arrays are not supported for the current target">;
 def note_vla_unsupported : Note<
   "variable length arrays are not supported for the current target">;
 
 // C99 variably modified types
 def err_variably_modified_template_arg : Error<
   "variably modified type %0 cannot be used as a template argument">;
def ext_enum_too_large : ExtWarn<
   "enumeration values exceed range of largest integer">, InGroup<EnumTooLarge>;
 def ext_enumerator_increment_too_large : ExtWarn<
   "incremented enumerator value %0 is not representable in the "
   "largest integer type">, InGroup<EnumTooLarge>;
 def warn_flag_enum_constant_out_of_range : Warning<
   "enumeration value %0 is out of range of flags in enumeration type %1">,
   InGroup<FlagEnum>;
 
-def warn_illegal_constant_array_size : Extension<
-  "size of static array must be an integer constant expression">;
 def err_vm_decl_in_file_scope : Error<
   "variably modified type declaration not allowed at file scope">;
 def err_vm_decl_has_extern_linkage : Error<
   "variably modified type declaration cannot have 'extern' linkage">;
 def err_typecheck_field_variable_size : Error<
   "fields must have a constant size: 'variable length array in structure' "
   "extension will never be supported">;
 def err_vm_func_decl : Error<

clang/lib/Sema/SemaDecl.cpp

if (const ParenType* PTy = dyn_cast<ParenType>(Ty)) {
     if (FixedType.isNull()) return FixedType;
     FixedType = Context.getParenType(FixedType);
     return Qs.apply(Context, FixedType);
   }
 
   const VariableArrayType* VLATy = dyn_cast<VariableArrayType>(T);
   if (!VLATy)
     return QualType();
-  // FIXME: We should probably handle this case
-  if (VLATy->getElementType()->isVariablyModifiedType())
+
+  QualType ElemTy = VLATy->getElementType();
+  if (ElemTy->isVariablyModifiedType()) {
+    ElemTy = TryToFixInvalidVariablyModifiedType(ElemTy, Context,
+                                                 SizeIsNegative, Oversized);
+    if (ElemTy.isNull())
       return QualType();
+  }
 
   Expr::EvalResult Result;
   if (!VLATy->getSizeExpr() ||
       !VLATy->getSizeExpr()->EvaluateAsInt(Result, Context))
     return QualType();
 
   llvm::APSInt Res = Result.Val.getInt();
 
   // Check whether the array size is negative.
   if (Res.isSigned() && Res.isNegative()) {
     SizeIsNegative = true;
     return QualType();
   }
 
   // Check whether the array is too large to be addressed.
-  unsigned ActiveSizeBits
-    = ConstantArrayType::getNumAddressingBits(Context, VLATy->getElementType(),
-                                              Res);
+  unsigned ActiveSizeBits =
+      (!ElemTy->isDependentType() && !ElemTy->isVariablyModifiedType() &&
+       !ElemTy->isIncompleteType() && !ElemTy->isUndeducedType())
+          ? ConstantArrayType::getNumAddressingBits(Context, ElemTy, Res)
+          : Res.getActiveBits();
   if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context)) {
     Oversized = Res;
     return QualType();
   }
 
-  return Context.getConstantArrayType(
-      VLATy->getElementType(), Res, VLATy->getSizeExpr(), ArrayType::Normal, 0);
+  return Context.getConstantArrayType(ElemTy, Res, VLATy->getSizeExpr(),
+                                      ArrayType::Normal, 0);
 }
 
 static void
 FixInvalidVariablyModifiedTypeLoc(TypeLoc SrcTL, TypeLoc DstTL) {
   SrcTL = SrcTL.getUnqualifiedLoc();
   DstTL = DstTL.getUnqualifiedLoc();
   if (PointerTypeLoc SrcPTL = SrcTL.getAs<PointerTypeLoc>()) {
     PointerTypeLoc DstPTL = DstTL.castAs<PointerTypeLoc>();
if (ParenTypeLoc SrcPTL = SrcTL.getAs<ParenTypeLoc>()) {
     DstPTL.setLParenLoc(SrcPTL.getLParenLoc());
     DstPTL.setRParenLoc(SrcPTL.getRParenLoc());
     return;
   }
   ArrayTypeLoc SrcATL = SrcTL.castAs<ArrayTypeLoc>();
   ArrayTypeLoc DstATL = DstTL.castAs<ArrayTypeLoc>();
   TypeLoc SrcElemTL = SrcATL.getElementLoc();
   TypeLoc DstElemTL = DstATL.getElementLoc();
+  if (VariableArrayTypeLoc SrcElemATL =
+          SrcElemTL.getAs<VariableArrayTypeLoc>()) {
+    ConstantArrayTypeLoc DstElemATL = DstElemTL.castAs<ConstantArrayTypeLoc>();
+    FixInvalidVariablyModifiedTypeLoc(SrcElemATL, DstElemATL);
+  } else {
     DstElemTL.initializeFullCopy(SrcElemTL);
+  }
   DstATL.setLBracketLoc(SrcATL.getLBracketLoc());
   DstATL.setSizeExpr(SrcATL.getSizeExpr());
   DstATL.setRBracketLoc(SrcATL.getRBracketLoc());
 }
 
 /// Helper method to turn variable array types into constant array
 /// types in certain situations which would otherwise be errors (for
 /// GCC compatibility).
if (T->isVariablyModifiedType()) {
     if (S->getFnParent() == nullptr) {
       bool SizeIsNegative;
       llvm::APSInt Oversized;
       TypeSourceInfo *FixedTInfo =
         TryToFixInvalidVariablyModifiedTypeSourceInfo(TInfo, Context,
                                                       SizeIsNegative,
                                                       Oversized);
       if (FixedTInfo) {
-        Diag(NewTD->getLocation(), diag::warn_illegal_constant_array_size);
+        Diag(NewTD->getLocation(), diag::ext_vla_folded_to_constant);
         NewTD->setTypeSourceInfo(FixedTInfo);
       } else {
         if (SizeIsNegative)
           Diag(NewTD->getLocation(), diag::err_typecheck_negative_array_size);
         else if (T->isVariableArrayType())
           Diag(NewTD->getLocation(), diag::err_vla_decl_in_file_scope);
         else if (Oversized.getBoolValue())
           Diag(NewTD->getLocation(), diag::err_array_too_large)
if (!FixedTInfo) {
       if (NewVD->isFileVarDecl())
         Diag(NewVD->getLocation(), diag::err_vm_decl_in_file_scope);
       else
         Diag(NewVD->getLocation(), diag::err_vm_decl_has_extern_linkage);
       NewVD->setInvalidDecl();
       return;
     }
 
-    Diag(NewVD->getLocation(), diag::warn_illegal_constant_array_size);
+    Diag(NewVD->getLocation(), diag::ext_vla_folded_to_constant);
     NewVD->setType(FixedT);
     NewVD->setTypeSourceInfo(FixedTInfo);
   }
 
   if (T->isVoidType()) {
     // C++98 [dcl.stc]p5: The extern specifier can be applied only to the names
     //                    of objects and functions.
     if (NewVD->isThisDeclarationADefinition() || getLangOpts().CPlusPlus) {
if (!InvalidDecl && T->isVariablyModifiedType()) {
     bool SizeIsNegative;
     llvm::APSInt Oversized;
 
     TypeSourceInfo *FixedTInfo =
       TryToFixInvalidVariablyModifiedTypeSourceInfo(TInfo, Context,
                                                     SizeIsNegative,
                                                     Oversized);
     if (FixedTInfo) {
-      Diag(Loc, diag::warn_illegal_constant_array_size);
+      Diag(Loc, diag::ext_vla_folded_to_constant);
       TInfo = FixedTInfo;
       T = FixedTInfo->getType();
     } else {
       if (SizeIsNegative)
         Diag(Loc, diag::err_typecheck_negative_array_size);
       else if (Oversized.getBoolValue())
         Diag(Loc, diag::err_array_too_large)
           << Oversized.toString(10);

clang/lib/Sema/SemaType.cpp

public:
     }
 
     Sema::SemaDiagnosticBuilder diagnoseFold(Sema &S,
                                              SourceLocation Loc) override {
       return S.Diag(Loc, diag::ext_vla_folded_to_constant);
     }
   } Diagnoser(VLADiag, VLAIsError);
 
-  // FIXME: GCC does *not* allow folding here in general; see PR44406.
-  // For GCC compatibility, we should remove this folding and leave it to
-  // TryFixVariablyModifiedType to convert VLAs to constant array types.
   ExprResult R = S.VerifyIntegerConstantExpression(
       ArraySize, &SizeVal, Diagnoser,
-      (S.LangOpts.GNUMode || S.LangOpts.OpenCL) ? Sema::AllowFold
-                                                : Sema::NoFold);
+      S.LangOpts.OpenCL ? Sema::AllowFold : Sema::NoFold);
   if (Diagnoser.IsVLA)
     return ExprResult();
   return R;
 }
 
 /// Build an array type.
 ///
 /// \param T The type of each element in the array.

clang/test/CXX/basic/basic.types/p10.cpp

 struct ArrBad {
   S s[3]; // expected-note {{data member 's' of non-literal type 'S [3]'}}
 };
 constexpr int f(ArrBad) { return 0; } // expected-error {{1st parameter type 'ArrBad' is not a literal type}}
 
 constexpr int arb(int n) {
   int a[n]; // expected-error {{variable of non-literal type 'int [n]' cannot be defined in a constexpr function}}
 }
+// expected-warning@+1 {{variable length array folded to constant array as an extension}}
 constexpr long Overflow[ // expected-error {{constexpr variable cannot have non-literal type 'long const[(1 << 30) << 2]'}}
     (1 << 30) << 2]{};   // expected-warning {{requires 34 bits to represent}}
 
 namespace inherited_ctor {
   struct A { constexpr A(int); };
   struct B : A {
     B();
     using A::A;

clang/test/CXX/drs/dr3xx.cpp

 namespace dr367 { // dr367: yes
   // FIXME: These diagnostics are terrible. Don't diagnose an ill-formed global
   // array as being a VLA!
   int a[true ? throw 0 : 4]; // expected-error 2{{variable length array}}
   int b[true ? 4 : throw 0];
   int c[true ? *new int : 4]; // expected-error 2{{variable length array}} expected-note {{read of uninitialized}}
   int d[true ? 4 : *new int];
 #if __cplusplus < 201103L
-  // expected-error@-4 {{variable length array}} expected-error@-4 {{constant expression}}
-  // expected-error@-3 {{variable length array}} expected-error@-3 {{constant expression}}
+  // expected-error@-4 2{{variable length array}}
+  // expected-error@-3 2{{variable length array}}
 #endif
 }
 
 namespace dr368 { // dr368: yes
   template<typename T, T> struct S {}; // expected-note {{here}}
   template<typename T> int f(S<T, T()> *); // expected-error {{function type}}
   //template<typename T> int g(S<T, (T())> *); // FIXME: crashes clang
   template<typename T> int g(S<T, true ? T() : T()> *); // expected-note {{cannot have type 'dr368::X'}}

clang/test/CodeGen/vla.c

 void test9(int n, int a[static n]) { }
 // NULL-INVALID: define void @test9(i32 %n, i32* nonnull align 4 %a)
 // NULL-VALID: define void @test9(i32 %n, i32* align 4 %a)
 
 // Make sure a zero-sized static array extent is still required to be nonnull.
 void test10(int a[static 0]) {}
 // NULL-INVALID: define void @test10(i32* nonnull align 4 %a)
 // NULL-VALID: define void @test10(i32* align 4 %a)
+
+const int constant = 32;
+// CHECK: define {{.*}}pr44406(
+int pr44406() {
+  int n = 0;
+  // Do not fold this VLA to an array of constant bound; that would miscompile
+  // this testcase.
+  char c[1][(constant - constant) + 3];
+  // CHECK: store i32 1,
+  sizeof(c[n = 1]);
+  return n;
+}

clang/test/Misc/warning-flags.c

 CHECK-NEXT:   warn_undef_interface
 CHECK-NEXT:   warn_undef_interface_suggest
 CHECK-NEXT:   warn_undef_protocolref
 CHECK-NEXT:   warn_weak_identifier_undeclared
 CHECK-NEXT:   warn_weak_import
 
 The list of warnings in -Wpedantic should NEVER grow.
 
-CHECK: Number in -Wpedantic (not covered by other -W flags): 27
+CHECK: Number in -Wpedantic (not covered by other -W flags): 26

clang/test/PCH/cxx-constexpr.cpp

 
 #define HEADER_INCLUDED
 extern const int a;
 const int b = a;
 
 #else
 
 const int a = 5;
-typedef int T[b]; // expected-error {{variable length array}} expected-error {{must be an integer constant expression}} expected-note {{initializer of 'b'}}
+typedef int T[b]; // expected-error 2{{variable length array}} expected-note {{initializer of 'b'}}
 // expected-note@14 {{here}}
 typedef int T[5];
 
 #endif

clang/test/Profile/misexpect-switch-default.c

 // Test that misexpect detects mis-annotated switch statements for default case
 
 // RUN: llvm-profdata merge %S/Inputs/misexpect-switch-default.proftext -o %t.profdata
 // RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
 
 int sum(int *buff, int size);
 int random_sample(int *buff, int size);
 int rand();
 void init_arry();
 
 const int inner_loop = 1000;
 const int outer_loop = 20;
-const int arry_size = 25;
+enum { arry_size = 25 };
 
 int arry[arry_size] = {0};
 
 int main() {
   init_arry();
   int val = 0;
   int j;
   for (j = 0; j < outer_loop * inner_loop; ++j) {

clang/test/Profile/misexpect-switch-nonconst.c

 // Test that misexpect emits no warning when switch condition is non-const
 
 // RUN: llvm-profdata merge %S/Inputs/misexpect-switch-nonconst.proftext -o %t.profdata
 // RUN: %clang_cc1 %s -O2 -o - -disable-llvm-passes -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify
 
 // expected-no-diagnostics
 int sum(int *buff, int size);
 int random_sample(int *buff, int size);
 int rand();
 void init_arry();
 
 const int inner_loop = 1000;
 const int outer_loop = 20;
-const int arry_size = 25;
+enum { arry_size = 25 };
 
 int arry[arry_size] = {0};
 
 int main() {
   init_arry();
   int val = 0;
 
   int j, k;

clang/test/Profile/misexpect-switch-only-default-case.c

 // Test that misexpect emits no warning when there is only one switch case
 
 // RUN: llvm-profdata merge %S/Inputs/misexpect-switch-default-only.proftext -o %t.profdata
 // RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
 
 // expected-no-diagnostics
 int sum(int *buff, int size);
 int random_sample(int *buff, int size);
 int rand();
 void init_arry();
 
 const int inner_loop = 1000;
 const int outer_loop = 20;
-const int arry_size = 25;
+enum { arry_size = 25 };
 
 int arry[arry_size] = {0};
 
 int main() {
   init_arry();
   int val = 0;
 
   int j, k;

clang/test/Profile/misexpect-switch.c

 // Test that misexpect detects mis-annotated switch statements
 
 // RUN: llvm-profdata merge %S/Inputs/misexpect-switch.proftext -o %t.profdata
 // RUN: %clang_cc1 %s -O2 -o - -emit-llvm -fprofile-instrument-use-path=%t.profdata -verify -Wmisexpect -debug-info-kind=line-tables-only
 
 int sum(int *buff, int size);
 int random_sample(int *buff, int size);
 int rand();
 void init_arry();
 
 const int inner_loop = 1000;
 const int outer_loop = 20;
-const int arry_size = 25;
+enum { arry_size = 25 };
 
 int arry[arry_size] = {0};
 
 int main() {
   init_arry();
   int val = 0;
 
   int j, k;

clang/test/Sema/builtin-assume.c

 #else
   __builtin_assume(i != 4);
   __builtin_assume(++i > 2); //expected-warning {{the argument to '__builtin_assume' has side effects that will be discarded}}
   __builtin_assume(nonconst() > 2); //expected-warning {{the argument to '__builtin_assume' has side effects that will be discarded}}
   __builtin_assume(isconst() > 2);
   __builtin_assume(ispure(i) > 2);
   __builtin_assume(ispure(++i) > 2); //expected-warning {{the argument to '__builtin_assume' has side effects that will be discarded}}
   
-  int test = sizeof(struct{char qq[(__builtin_assume(i != 5), 7)];});
+  int test = sizeof(struct{char qq[(__builtin_assume(i != 5), 7)];}); // expected-warning {{variable length array}}
 #endif
   return a[i];
 }
 

clang/test/Sema/builtins.c

 typedef int __attribute__((vector_size(16))) IntVector;
 struct Aggregate { int n; char c; };
 enum Enum { EnumValue1, EnumValue2 };
 
 typedef __typeof(sizeof(int)) size_t;
 size_t strlen(const char *);
 
 void test17() {
-#define ASSERT(...) { int arr[(__VA_ARGS__) ? 1 : -1]; }
+#define ASSERT(...) { enum { folded = (__VA_ARGS__) }; int arr[folded ? 1 : -1]; }
 #define T(...) ASSERT(__builtin_constant_p(__VA_ARGS__))
 #define F(...) ASSERT(!__builtin_constant_p(__VA_ARGS__))
 
   // __builtin_constant_p returns 1 if the argument folds to:
   //  - an arithmetic constant with value which is known at compile time
   T(test17_n);
   T(&test17_c[3] - test17_c);
   T(3i + 5); // expected-warning {{imaginary constant}}
#define F(...) ASSERT(!__builtin_constant_p(__VA_ARGS__))
   // Ensure that a technique used in glibc is handled correctly.
 #define OPT(...) (__builtin_constant_p(__VA_ARGS__) && strlen(__VA_ARGS__) < 4)
   // FIXME: These are incorrectly treated as ICEs because strlen is treated as
   // a builtin.
   ASSERT(OPT("abc"));
   ASSERT(!OPT("abcd"));
   // In these cases, the strlen is non-constant, but the __builtin_constant_p
   // is 0: the array size is not an ICE but is foldable.
-  ASSERT(!OPT(test17_c));        // expected-warning {{folded}}
-  ASSERT(!OPT(&test17_c[0]));    // expected-warning {{folded}}
-  ASSERT(!OPT((char*)test17_c)); // expected-warning {{folded}}
-  ASSERT(!OPT(test17_d));        // expected-warning {{folded}}
-  ASSERT(!OPT(&test17_d[0]));    // expected-warning {{folded}}
-  ASSERT(!OPT((char*)test17_d)); // expected-warning {{folded}}
+  ASSERT(!OPT(test17_c));        // expected-warning {{folding}}
+  ASSERT(!OPT(&test17_c[0]));    // expected-warning {{folding}}
+  ASSERT(!OPT((char*)test17_c)); // expected-warning {{folding}}
+  ASSERT(!OPT(test17_d));        // expected-warning {{folding}}
+  ASSERT(!OPT(&test17_d[0]));    // expected-warning {{folding}}
+  ASSERT(!OPT((char*)test17_d)); // expected-warning {{folding}}
 
 #undef OPT
 #undef T
 #undef F
 }
 
 void test18() {
   char src[1024];

clang/test/Sema/complex-int.c

 void test4(_Complex float *x) {
   *x = ~*x;
 }
 
 void test5(_Complex int *x) {
   (*x)++;
 }
 
-int i1[(2+3i)*(5+7i) == 29i-11 ? 1 : -1];
-int i2[(29i-11)/(5+7i) == 2+3i ? 1 : -1];
-int i3[-(2+3i) == +(-3i-2) ? 1 : -1];
-int i4[~(2+3i) == 2-3i ? 1 : -1];
-int i5[(3i == -(-3i) ? ((void)3, 1i - 1) : 0) == 1i - 1 ? 1 : -1];
-
-int f1[(2.0+3.0i)*(5.0+7.0i) == 29.0i-11.0 ? 1 : -1];
-int f2[(29.0i-11.0)/(5.0+7.0i) == 2.0+3.0i ? 1 : -1];
-int f3[-(2.0+3.0i) == +(-3.0i-2.0) ? 1 : -1];
-int f4[~(2.0+3.0i) == 2.0-3.0i ? 1 : -1];
-int f5[(3.0i == -(-3.0i) ? ((void)3.0, __extension__ (1.0i - 1.0)) : 0) == 1.0i - 1.0 ? 1 : -1];
+// None of these array bounds is an ICE due to the use of literals of
+// non-integer type. But we can constant-fold all of them.
+int i1[(2+3i)*(5+7i) == 29i-11 ? 1 : -1]; // expected-warning {{fold}}
+int i2[(29i-11)/(5+7i) == 2+3i ? 1 : -1]; // expected-warning {{fold}}
+int i3[-(2+3i) == +(-3i-2) ? 1 : -1]; // expected-warning {{fold}}
+int i4[~(2+3i) == 2-3i ? 1 : -1]; // expected-warning {{fold}}
+int i5[(3i == -(-3i) ? ((void)3, 1i - 1) : 0) == 1i - 1 ? 1 : -1]; // expected-warning {{fold}}
+
+int f1[(2.0+3.0i)*(5.0+7.0i) == 29.0i-11.0 ? 1 : -1]; // expected-warning {{fold}}
+int f2[(29.0i-11.0)/(5.0+7.0i) == 2.0+3.0i ? 1 : -1]; // expected-warning {{fold}}
+int f3[-(2.0+3.0i) == +(-3.0i-2.0) ? 1 : -1]; // expected-warning {{fold}}
+int f4[~(2.0+3.0i) == 2.0-3.0i ? 1 : -1]; // expected-warning {{fold}}
+int f5[(3.0i == -(-3.0i) ? ((void)3.0, __extension__ (1.0i - 1.0)) : 0) == 1.0i - 1.0 ? 1 : -1]; // expected-warning {{fold}}

clang/test/Sema/const-eval-64.c

 // RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-linux %s
-// expected-no-diagnostics
 
 #define EVAL_EXPR(testno, expr) int test##testno = sizeof(struct{char qq[expr];});
 
 // <rdar://problem/10962435>
-EVAL_EXPR(1, ((char*)-1LL) + 1 == 0 ? 1 : -1)
-EVAL_EXPR(2, ((char*)-1LL) + 1 < (char*) -1 ? 1 : -1)
+EVAL_EXPR(1, ((char*)-1LL) + 1 == 0 ? 1 : -1) // expected-warning {{folded}}
+EVAL_EXPR(2, ((char*)-1LL) + 1 < (char*) -1 ? 1 : -1) // expected-warning {{folded}}

clang/test/Sema/const-eval.c

 // RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-linux %s -Wno-tautological-pointer-compare -Wno-pointer-to-int-cast
 
-#define EVAL_EXPR(testno, expr) int test##testno = sizeof(struct{char qq[expr];});
+#define EVAL_EXPR(testno, expr) enum { test##testno = (expr) }; struct check_positive##testno { int a[test##testno]; };
 int x;
 EVAL_EXPR(1, (_Bool)&x)
 EVAL_EXPR(2, (int)(1.0+(double)4))
 EVAL_EXPR(3, (int)(1.0+(float)4.0))
 EVAL_EXPR(4, (_Bool)(1 ? (void*)&x : 0))
 EVAL_EXPR(5, (_Bool)(int[]){0})
 struct y {int x,y;};
 EVAL_EXPR(6, (int)(1+(struct y*)0))
 EVAL_EXPR(7, (int)&((struct y*)0)->y)
 EVAL_EXPR(8, (_Bool)"asdf")
 EVAL_EXPR(9, !!&x)
 EVAL_EXPR(10, ((void)1, 12))
 void g0(void);
-EVAL_EXPR(11, (g0(), 12)) // expected-error {{must have a constant size}}
+EVAL_EXPR(11, (g0(), 12)) // expected-error {{not an integer constant expression}}
 EVAL_EXPR(12, 1.0&&2.0)
-EVAL_EXPR(13, x || 3.0) // expected-error {{must have a constant size}}
+EVAL_EXPR(13, x || 3.0) // expected-error {{not an integer constant expression}}
 
 unsigned int l_19 = 1;
-EVAL_EXPR(14, (1 ^ l_19) && 1); // expected-error {{fields must have a constant size}}
+EVAL_EXPR(14, (1 ^ l_19) && 1); // expected-error {{not an integer constant expression}}
 
 void f()
 {
   int a;
   EVAL_EXPR(15, (_Bool)&a);
 }
 
 // FIXME: Turn into EVAL_EXPR test once we have more folding.
 _Complex float g16 = (1.0f + 1.0fi);
 
 // ?: in constant expressions.
 int g17[(3?:1) - 2]; 
 
 EVAL_EXPR(18, ((int)((void*)10 + 10)) == 20 ? 1 : -1);
 
 struct s {
-  int a[(int)-1.0f]; // expected-error {{'a' declared as an array with a negative size}}
+  int a[(int)-1.0f]; // expected-error {{array size is negative}}
 };
 
 EVAL_EXPR(19, ((int)&*(char*)10 == 10 ? 1 : -1));
 
 EVAL_EXPR(20, __builtin_constant_p(*((int*) 10)));
 
 EVAL_EXPR(21, (__imag__ 2i) == 2 ? 1 : -1);
 
 EVAL_EXPR(22, (__real__ (2i+3)) == 3 ? 1 : -1);
 
-int g23[(int)(1.0 / 1.0)] = { 1 };
-int g24[(int)(1.0 / 1.0)] = { 1 , 2 }; // expected-warning {{excess elements in array initializer}}
-int g25[(int)(1.0 + 1.0)], g26 = sizeof(g25);
+int g23[(int)(1.0 / 1.0)] = { 1 }; // expected-warning {{folded to constant array}}
+int g24[(int)(1.0 / 1.0)] = { 1 , 2 }; // expected-warning {{folded to constant array}} expected-warning {{excess elements in array initializer}}
+int g25[(int)(1.0 + 1.0)], g26 = sizeof(g25); // expected-warning {{folded to constant array}}
 
 EVAL_EXPR(26, (_Complex double)0 ? -1 : 1)
 EVAL_EXPR(27, (_Complex int)0 ? -1 : 1)
 EVAL_EXPR(28, (_Complex double)1 ? 1 : -1)
 EVAL_EXPR(29, (_Complex int)1 ? 1 : -1)
 
 
 // PR4027 + rdar://6808859

 
 // PR11391.
 struct PR11391 { _Complex float f; } pr11391;
 EVAL_EXPR(42, __builtin_constant_p(pr11391.f = 1))
 
 // PR12043
 float varfloat;
 const float constfloat = 0;
-EVAL_EXPR(43, varfloat && constfloat) // expected-error {{must have a constant size}}
+EVAL_EXPR(43, varfloat && constfloat) // expected-error {{not an integer constant expression}}
 
 // <rdar://problem/10962435>
 EVAL_EXPR(45, ((char*)-1) + 1 == 0 ? 1 : -1)
 EVAL_EXPR(46, ((char*)-1) + 1 < (char*) -1 ? 1 : -1)
 EVAL_EXPR(47, &x < &x + 1 ? 1 : -1)
 EVAL_EXPR(48, &x != &x - 1 ? 1 : -1)
-EVAL_EXPR(49, &x < &x - 100 ? 1 : -1) // expected-error {{must have a constant size}}
+EVAL_EXPR(49, &x < &x - 100 ? 1 : -1) // expected-error {{not an integer constant expression}}
 
 extern struct Test50S Test50;
-EVAL_EXPR(50, &Test50 < (struct Test50S*)((unsigned long)&Test50 + 10)) // expected-error {{must have a constant size}}
+EVAL_EXPR(50, &Test50 < (struct Test50S*)((unsigned long)&Test50 + 10)) // expected-error {{not an integer constant expression}}
 
 // <rdar://problem/11874571>
 EVAL_EXPR(51, 0 != (float)1e99)
 
 // PR21945
 void PR21945() { int i = (({}), 0l); }
 
 void PR24622();
 struct PR24622 {} pr24622;
-EVAL_EXPR(52, &pr24622 == (void *)&PR24622); // expected-error {{must have a constant size}}
+EVAL_EXPR(52, &pr24622 == (void *)&PR24622); // expected-error {{not an integer constant expression}}
 
 // We evaluate these by providing 2s' complement semantics in constant
 // expressions, like we do for integers.
 void *PR28739a = (__int128)(unsigned long)-1 + &PR28739a;
 void *PR28739b = &PR28739b + (__int128)(unsigned long)-1;
 __int128 PR28739c = (&PR28739c + (__int128)(unsigned long)-1) - &PR28739c;
 void *PR28739d = &(&PR28739d)[(__int128)(unsigned long)-1];
 
 struct PR35214_X {
   int k;
   int arr[];
 };
 int PR35214_x;
 int PR35214_y = ((struct PR35214_X *)&PR35214_x)->arr[1]; // expected-error {{not a compile-time constant}}
 int *PR35214_z = &((struct PR35214_X *)&PR35214_x)->arr[1]; // ok, &PR35214_x + 2

clang/test/Sema/darwin-align-cast.c

 // RUN: %clang_cc1 -fsyntax-only -Wno-pointer-to-int-cast -verify %s
-// expected-no-diagnostics
 typedef long unsigned int __darwin_size_t;
 typedef long __darwin_ssize_t;
 typedef __darwin_size_t size_t;
 typedef __darwin_ssize_t ssize_t;
 
 struct cmsghdr {};
 
 #if 0
 This code below comes from the following system headers:
 sys/socket.h:#define CMSG_SPACE(l) (__DARWIN_ALIGN(sizeof(struct  
 cmsghdr)) + __DARWIN_ALIGN(l))
 
 i386/_param.h:#define __DARWIN_ALIGN(p) ((__darwin_size_t)((char *)(p)  
 + __DARWIN_ALIGNBYTES) &~ __DARWIN_ALIGNBYTES)
 #endif
 
 ssize_t sendFileDescriptor(int fd, void *data, size_t nbytes, int sendfd) {
   union {
+    // expected-warning@+1 {{folded to constant array}}
     char control[(((__darwin_size_t)((char *)(sizeof(struct cmsghdr)) + (sizeof(__darwin_size_t) - 1)) &~ (sizeof(__darwin_size_t) - 1)) + ((__darwin_size_t)((char *)(sizeof(int)) + (sizeof(__darwin_size_t) - 1)) &~ (sizeof(__darwin_size_t) - 1)))];
   } control_un;
   return 0;
 }
 

clang/test/Sema/decl-in-prototype.c

 
 // Only warn once, even if we create two declarations.
 void f(struct q *, struct __attribute__((aligned(4))) q *); // expected-warning {{will not be visible outside}}
 
 // This enum inside the function pointer parameter shouldn't leak into the
 // function.
 enum { BB = 0 };
 void enum_in_fun_in_fun(void (*fp)(enum { AA, BB } e)) { // expected-warning {{will not be visible}}
-  SA(1, AA == 5);
+  SA(1, AA == 5); // expected-error {{variable-sized object may not be initialized}}
   SA(2, BB == 0);
 }
 
 void f7() {
   extern void ext(struct S { enum E7 { a, b } o; } p); // expected-warning 2 {{will not be visible}}
   ext(a); // expected-error {{use of undeclared identifier}}
 }
 

clang/test/Sema/gnu-flags.c

 // expected-warning@+5 {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}
 // expected-warning@+7 {{variable length array folded to constant array as an extension}}
 #endif
 
 enum {
   fic = (int)(0.75 * 1000 * 1000)
 };
 static const int size = 100;
-void foo(void) { int data[size]; }
+int data[size];
+
+void foo(void) { int data[size]; } // OK, always a VLA
 
 #if ALL || REDECLAREDENUM
 // expected-note@+4 {{previous definition is here}}
 // expected-warning@+8 {{redeclaration of already-defined enum 'RE' is a GNU extension}}
 #endif
 
 enum RE {
   Val1,

clang/test/Sema/i-c-e.c

 // RUN: %clang_cc1 %s -ffreestanding -Wno-int-to-pointer-cast -fsyntax-only -verify -pedantic -fpascal-strings -std=c99
 
 #include <stdint.h>
 #include <limits.h>
 
 int a() {int p; *(1 ? &p : (void*)(0 && (a(),1))) = 10;} // expected-error {{incomplete type 'void' is not assignable}}
 
 // rdar://6091492 - ?: with __builtin_constant_p as the operand is an i-c-e.
 int expr;
 char w[__builtin_constant_p(expr) ? expr : 1];
 
 char v[sizeof(__builtin_constant_p(0)) == sizeof(int) ? 1 : -1];
 
 int implicitConversion = 1.0;
-char floatArith[(int)(1.0+2.0)]; // expected-warning {{must be an integer constant expression}}
+char floatArith[(int)(1.0+2.0)]; // expected-warning {{variable length array folded to constant array as an extension}}
 
 // __builtin_constant_p as the condition of ?: allows arbitrary foldable
 // constants to be transmogrified into i-c-e's.
 char b[__builtin_constant_p((int)(1.0+2.0)) ? (int)(1.0+2.0) : -1];
 
 struct c {
   int a : (
            __builtin_constant_p((int)(1.0+2.0)) ? (int)(1.0+

 int expr;
 char y[__builtin_constant_p(expr) ? -1 : 1];
 char z[__builtin_constant_p(4) ? 1 : -1];
 
 // Comma tests
 int comma1[0?1,2:3];
 int comma2[1||(1,2)]; // expected-warning {{use of logical '||' with constant operand}} \
                       // expected-note {{use '|' for a bitwise operation}}
-int comma3[(1,2)]; // expected-warning {{size of static array must be an integer constant expression}}
+int comma3[(1,2)]; // expected-warning {{variable length array folded to constant array as an extension}}
 
 // Pointer + __builtin_constant_p
 char pbcp[__builtin_constant_p(4) ? (intptr_t)&expr : 0]; // expected-error {{variable length array declaration not allowed at file scope}}
 
 int illegaldiv1a[1 || 1/0];
 int illegaldiv1b[1 && 1/0];  //expected-error{{variable length array declaration not allowed at file scope}}
 
 int illegaldiv2[1/0]; // expected-error {{variable length array declaration not allowed at file scope}}

clang/test/Sema/offsetof-64.c

 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-linux-gnu
 
 // PR15216
 // Don't crash when taking computing the offset of structs with large arrays.
 const unsigned long Size = (1l << 60);
 
 struct Chunk1 {
-  char padding[Size];
-  char more_padding[1][Size];
+  char padding[Size]; // expected-warning {{folded to constant}}
+  char more_padding[1][Size]; // expected-warning {{folded to constant}}
   char data;
 };
 
 int test1 = __builtin_offsetof(struct Chunk1, data);
 
 struct Chunk2 {
-  char padding[Size][Size][Size];  // expected-error 2{{array is too large}}
+  char padding[Size][Size][Size];  // expected-error {{array is too large}}
   char data;
 };
 
 // FIXME: Remove this error when the constant evaluator learns to
 // ignore bad types.
 int test2 = __builtin_offsetof(struct Chunk2, data);  // expected-error{{initializer element is not a compile-time constant}} 

clang/test/Sema/struct-decl.c

 // RUN: %clang_cc1 -Wno-pointer-to-int-cast -fsyntax-only -verify %s
 // PR3459
 struct bar {
   char n[1];
 };
 
 struct foo {
-  char name[(int)&((struct bar *)0)->n];
-  char name2[(int)&((struct bar *)0)->n - 1]; //expected-error{{'name2' declared as an array with a negative size}}
+  char name[(int)&((struct bar *)0)->n]; // expected-warning {{folded to constant}}
+  char name2[(int)&((struct bar *)0)->n - 1]; // expected-error {{array size is negative}}
 };
 
 // PR3430
 struct s {
   struct st {
     int v;
   } *ts;
 };

clang/test/Sema/typedef-variable-type.c

 // RUN: %clang_cc1 %s -verify -fsyntax-only -pedantic -Wno-typedef-redefinition -std=c99
 
 // Make sure we accept a single typedef
-typedef int (*a)[!.0]; // expected-warning{{size of static array must be an integer constant expression}}
+typedef int (*a)[!.0]; // expected-warning{{folded to constant array}}
 
 // And make sure we accept identical redefinitions in system headers
 // (The test uses -Wno-typedef-redefinition to simulate this.)
-typedef int (*a)[!.0]; // expected-warning{{size of static array must be an integer constant expression}}
+typedef int (*a)[!.0]; // expected-warning{{folded to constant array}}

clang/test/Sema/vla.c

 int f4(int a[*][*]);
 
 // PR2044
 int pr2044(int b) {int (*c(void))[b];**c() = 2;} // expected-error {{variably modified type}}
 int pr2044b;
 int (*pr2044c(void))[pr2044b]; // expected-error {{variably modified type}}
 
 const int f5_ci = 1;
-void f5() { char a[][f5_ci] = {""}; } // expected-warning {{variable length array folded to constant array as an extension}}
+void f5() { char a[][f5_ci] = {""}; } // expected-error {{variable-sized object may not be initialized}}
 
 // PR5185
 void pr5185(int a[*]);
 void pr5185(int a[*]) // expected-error {{variable length array must be bound in function definition}}
 {
 }
 
 void pr23151(int (*p1)[*]) // expected-error {{variable length array must be bound in function definition}}
void VLAPtrAssign(int size) {
   // Last array dimension too large
   int (*p2)[2][3][size][4][6] = array; // expected-warning {{incompatible pointer types}}
   // Second array dimension too large
   int (*p3)[20][3][size][4][5] = array; // expected-warning {{incompatible pointer types}}
 
   // Not illegal in C, program _might_ be well formed if size == 3.
   int (*p4)[2][size][3][4][5] = array;
 }
+
+void pr44406() {
+  goto L; // expected-error {{cannot jump}}
+  int z[(int)(1.0 * 2)]; // expected-note {{bypasses initialization of variable length array}}
+L:;
+}
+
+const int pr44406_a = 32;
+typedef struct {
+  char c[pr44406_a]; // expected-warning {{folded to constant array as an extension}}
+} pr44406_s;

clang/test/SemaCXX/anonymous-struct.cpp

typedef struct { // expected-error 0-1{{unsupported}}
     enum X {};
     int arr[Y<X>::value];
   } B; // expected-note 0-1{{by this typedef}}
 
   template<typename T> void f() {}
   typedef struct { // expected-error {{unsupported}}
     enum X {};
     int arr[&f<X> ? 1 : 2];
+#if __cplusplus < 201103L
+    // expected-warning@-2 {{folded to constant}}
+#endif
   } C; // expected-note {{by this typedef}}
 }
 
 namespace ImplicitDecls {
 struct Destructor {
   ~Destructor() {}
 };
 typedef struct {

clang/test/SemaCXX/constant-expression.cpp

 
 extern const int recurse1;
 // recurse2 cannot be used in a constant expression because it is not
 // initialized by a constant expression. The same expression appearing later in
 // the TU would be a constant expression, but here it is not.
 const int recurse2 = recurse1; // expected-note {{here}}
 const int recurse1 = 1;
 int array1[recurse1]; // ok
-int array2[recurse2]; // expected-warning {{variable length array}} expected-warning {{integer constant expression}} expected-note {{initializer of 'recurse2' is not a constant expression}}
+int array2[recurse2]; // expected-warning 2{{variable length array}} expected-note {{initializer of 'recurse2' is not a constant expression}}
 
 namespace FloatConvert {
   typedef int a[(int)42.3];
   typedef int a[(int)42.997];
   typedef int b[(long long)4e20]; // expected-warning {{variable length}} expected-error {{variable length}} expected-warning {{'long long' is a C++11 extension}} expected-note {{value 4.0E+20 is outside the range of representable values}}
 }
 
 // PR12626

clang/test/SemaCXX/cxx1z-noexcept-function-type.cpp

 }
 
 namespace Builtins {
   // Pick two functions that ought to have the same noexceptness.
   extern "C" int strcmp(const char *, const char *);
   extern "C" int strncmp(const char *, const char *, decltype(sizeof(0))) noexcept;
 
   // Check we recognized both as builtins.
-  typedef int arr[strcmp("bar", "foo") + 4 * strncmp("foo", "bar", 4)];
+  typedef int arr[strcmp("bar", "foo") + 4 * strncmp("foo", "bar", 4)]; // expected-warning {{variable length array}}
   typedef int arr[3];
 }
 
 namespace ExplicitInstantiation {
   template<typename T> void f() noexcept {}
   template<typename T> struct X { void f() noexcept {} };
   template void f<int>();
   template void X<int>::f();

clang/test/SemaCXX/i-c-e-cxx.cpp

 
 // This isn't an integral constant expression, but make sure it folds anyway.
 struct PR8836 { char _; long long a; };
 #if __cplusplus <= 199711L
 // expected-warning@-2 {{'long long' is a C++11 extension}}
 #endif
 
 int PR8836test[(__typeof(sizeof(int)))&reinterpret_cast<const volatile char&>((((PR8836*)0)->a))];
-// expected-warning@-1 {{folded to constant array as an extension}}
+// expected-warning@-1 0-1{{C99 feature}} expected-warning@-1 {{folded to constant array as an extension}}
 // expected-note@-2 {{cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression}}
 
 const int nonconst = 1.0;
 #if __cplusplus <= 199711L
 // expected-note@-2 {{declared here}}
 #endif
 int arr[nonconst];
 #if __cplusplus <= 199711L
-// expected-warning@-2 {{folded to constant array as an extension}}
+// expected-warning@-2 0-1{{C99 feature}} expected-warning@-2 {{folded to constant array as an extension}}
 // expected-note@-3 {{initializer of 'nonconst' is not a constant expression}}
 #endif
 
 const int castfloat = static_cast<int>(1.0);
 int arr2[castfloat]; // ok

clang/test/SemaObjC/gcc-cast-ext.m

 // RUN: %clang_cc1 -verify -Wno-pointer-to-int-cast -Wno-objc-root-class %s
 @class NSInvocation, NSMethodSignature, NSCoder, NSString, NSEnumerator;
 typedef struct _NSRange { } NSRange;
 
 @class PBXFileReference;
 
 @interface PBXDocBookmark
 + alloc;  // expected-note {{method 'alloc' declared here}}
 - autorelease;  // expected-note {{method 'autorelease' declared here}}
 @end
 
 // GCC allows pointer expressions in integer constant expressions.
 struct {
-  char control[((int)(char *)2)];
+  char control[((int)(char *)2)]; // expected-warning {{extension}}
 } xx;
 
 @implementation PBXDocBookmark // expected-warning {{method definition for 'autorelease' not found}}\
                                // expected-warning {{method definition for 'alloc' not found}}
 
 + (id)bookmarkWithFileReference:(PBXFileReference *)fileRef gylphRange:(NSRange)range anchor:(NSString *)htmlAnchor
 {
     NSRange r = (NSRange)range;
     return [[[self alloc] initWithFileReference:fileRef gylphRange:(NSRange)range anchor:(NSString *)htmlAnchor] autorelease];  // expected-warning {{method '-initWithFileReference:gylphRange:anchor:' not found (return type defaults to 'id')}}
 }
 @end