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Support the zero-initialization of VLAs when that really means a zero 

bit-pattern.  Continue punting on zero-initializing VLAs with a nonzero
pattern.

llvm-svn: 123439
This commit is contained in:
John McCall 2011-01-14 10:37:58 +00:00
parent 5461a7523f
commit a08ffd22d5
1 changed files with 20 additions and 8 deletions
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28
clang/lib/CodeGen/CodeGenFunction.cpp
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@ -543,15 +543,31 @@ CodeGenFunction::EmitNullInitialization(llvm::Value *DestPtr, QualType Ty) {
uint64_t Size = TypeInfo.first / 8;
unsigned Align = TypeInfo.second / 8;
// Don't bother emitting a zero-byte memset.
if (Size == 0)
return;
llvm::Value *SizeVal;
bool vla;
llvm::ConstantInt *SizeVal = llvm::ConstantInt::get(IntPtrTy, Size);
// Don't bother emitting a zero-byte memset.
if (Size == 0) {
// But note that getTypeInfo returns 0 for a VLA.
if (const VariableArrayType *vlaType =
dyn_cast_or_null<VariableArrayType>(
getContext().getAsArrayType(Ty))) {
SizeVal = GetVLASize(vlaType);
vla = true;
} else {
return;
}
} else {
SizeVal = llvm::ConstantInt::get(IntPtrTy, Size);
vla = false;
}
// If the type contains a pointer to data member we can't memset it to zero.
// Instead, create a null constant and copy it to the destination.
if (!CGM.getTypes().isZeroInitializable(Ty)) {
// FIXME: variable-size types!
if (vla) return;
llvm::Constant *NullConstant = CGM.EmitNullConstant(Ty);
llvm::GlobalVariable *NullVariable =
@ -562,8 +578,6 @@ CodeGenFunction::EmitNullInitialization(llvm::Value *DestPtr, QualType Ty) {
llvm::Value *SrcPtr =
Builder.CreateBitCast(NullVariable, Builder.getInt8PtrTy());
// FIXME: variable-size types?
// Get and call the appropriate llvm.memcpy overload.
Builder.CreateMemCpy(DestPtr, SrcPtr, SizeVal, Align, false);
return;
@ -572,8 +586,6 @@ CodeGenFunction::EmitNullInitialization(llvm::Value *DestPtr, QualType Ty) {
// Otherwise, just memset the whole thing to zero. This is legal
// because in LLVM, all default initializers (other than the ones we just
// handled above) are guaranteed to have a bit pattern of all zeros.
// FIXME: Handle variable sized types.
Builder.CreateMemSet(DestPtr, Builder.getInt8(0), SizeVal, Align, false);
}