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[Clang][Sema] placement new initializes typedef array with correct size #83124

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Merged
merged 1 commit into from
Apr 16, 2024
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[Clang][Sema] placement new initializes typedef array with correct size #83124

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2 changes: 2 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -539,6 +539,8 @@ Bug Fixes to C++ Support
Fixes (#GH70604), (#GH79754), (#GH84163), (#GH84425), (#GH86054), (#GH86398), and (#GH86399).
- Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
- Fix a crash in requires expression with templated base class member function. Fixes (#GH84020).
- placement new initializes typedef array with correct size
(`#GH41441 <https://github.com/llvm/llvm-project/issues/41441>`_)

Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
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14 changes: 13 additions & 1 deletion clang/lib/Sema/TreeTransform.h
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Expand Up @@ -12802,6 +12802,19 @@ TreeTransform<Derived>::TransformCXXNewExpr(CXXNewExpr *E) {
ArraySize = NewArraySize.get();
}

// Per C++0x [expr.new]p5, the type being constructed may be a
// typedef of an array type.
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This comment doesn't really match what is happening below? the 'if' is still based on 'ArraySize' (presumably you mean this to be a proxy for E->isArray?). But there is no standardeeze quoted here about why you'd pick up the size/alloc type from it like this, rather than in the E->isArray above.

Also, does this also handle cases where this is going to still be dependent?

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Yes, you're right. It's proxy for E->isArray(), but the condition just before checks if it's Array and then calculates the ArraySize. I didn't want to check again and used the ArraySize calculated before. If the earlier condition E->isArray() fails then ArraySize won't be calculated and if(ArraySize) would also fail. In Typedef case Tarray x; the alloctype is Tarray for x, that's why using Tarray Element Type which is int, and using that as allocType. Yes, this is for dependent cases only.

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So it seems this should probably be inside of that E->isArray() block instead then?

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Yes, it can be inside that block, but in the non-dependent it was outside the block to check for typedef so I followed the same thing here as well. It's in Sema::SemaExprCXX::BuildNEWCXX.

QualType AllocType = AllocTypeInfo->getType();
if (ArraySize) {
if (const ConstantArrayType *Array =
SemaRef.Context.getAsConstantArrayType(AllocType)) {
ArraySize = IntegerLiteral::Create(SemaRef.Context, Array->getSize(),
SemaRef.Context.getSizeType(),
E->getBeginLoc());
AllocType = Array->getElementType();
}
}

// Transform the placement arguments (if any).
bool ArgumentChanged = false;
SmallVector<Expr*, 8> PlacementArgs;
Expand Down Expand Up @@ -12863,7 +12876,6 @@ TreeTransform<Derived>::TransformCXXNewExpr(CXXNewExpr *E) {
return E;
}

QualType AllocType = AllocTypeInfo->getType();
if (!ArraySize) {
// If no array size was specified, but the new expression was
// instantiated with an array type (e.g., "new T" where T is
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20 changes: 20 additions & 0 deletions clang/test/SemaCXX/instantiate-new-placement-size.cpp
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@@ -0,0 +1,20 @@
// RUN: %clang -S -fno-discard-value-names -emit-llvm -o - %s | FileCheck %s
// Issue no: 41441
#include <new>

// CHECK: call void @llvm.memset.p0.i64(ptr align 1 %x, i8 0, i64 8, i1 false)
// CHECK: call void @llvm.memset.p0.i64(ptr align 16 %x, i8 0, i64 32, i1 false)
template <typename TYPE>
void f()
{
typedef TYPE TArray[8];

TArray x;
new(&x) TArray();
}

int main()
{
f<char>();
f<int>();
}