When an array is created that is too large, return QualType() instead of a valid type.

[rsmith]

lib/Sema/SemaType.cpp

1556–1559

How about just returning QualType() here? An invalid type should do a better job of suppressing follow-on diagnostics than an array-of-unexpected-size.

[rtrieu]

lib/Sema/SemaType.cpp

1556–1559

Returning QualType() also would prevent the crash, however it also causes a new error to be emitted. "initializer element is not a compile-time constant" on __builtin_offsetof(struct Chunk2, data).

[rtrieu]

When a too large array is requested, use QualType() to indicate there is not a valid type being created.

[rsmith]

LGTM

[rtrieu]

Committed in r181970.

lib/Sema/SemaType.cpp

if (ConstVal == 0) {
           << ArraySize->getSourceRange();
         ASM = ArrayType::Normal;
       }
     } else if (!T->isDependentType() && !T->isVariablyModifiedType() &&
                !T->isIncompleteType()) {
       // Is the array too large?
       unsigned ActiveSizeBits
         = ConstantArrayType::getNumAddressingBits(Context, T, ConstVal);
-      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context))
+      if (ActiveSizeBits > ConstantArrayType::getMaxSizeBits(Context)) {
         Diag(ArraySize->getLocStart(), diag::err_array_too_large)
           << ConstVal.toString(10)
           << ArraySize->getSourceRange();
+        return QualType();
+      }
     }
 
     T = Context.getConstantArrayType(T, ConstVal, ASM, Quals);
   }
 
   // OpenCL v1.2 s6.9.d: variable length arrays are not supported.
   if (getLangOpts().OpenCL && T->isVariableArrayType()) {
     Diag(Loc, diag::err_opencl_vla);
     return QualType();
   }

test/Sema/offsetof-64.c

 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-linux-gnu
-// expected-no-diagnostics
 
 // PR15216
 // Don't crash when taking computing the offset of structs with large arrays.
 const unsigned long Size = (1l << 62);
 
-struct Chunk {
+struct Chunk1 {
   char padding[Size];
   char more_padding[1][Size];
   char data;
 };
 
-int test1 = __builtin_offsetof(struct Chunk, data);
+int test1 = __builtin_offsetof(struct Chunk1, data);
 
+struct Chunk2 {
+  char padding[Size][Size][Size];  // expected-error 2{{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}}