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[CodeGen] Fix handling of nullptr in initializers #137364

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Merged
alexfh merged 5 commits into from
Apr 28, 2025
Merged

[CodeGen] Fix handling of nullptr in initializers #137364

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5431de1
[CodeGen] Fix handling of nullptr in initializers
alexfh Apr 25, 2025
a0e4f30
Update CK_NullToPointer comment
alexfh Apr 25, 2025
74e4ed2
Move the test to nullptr.cpp, simplified it, added CHECK-LABEL.
alexfh Apr 25, 2025
f5d1430
Update CK_NullToPointer comment
alexfh Apr 25, 2025
c68b2ef
Update OperationKinds.def
alexfh Apr 25, 2025
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1 change: 1 addition & 0 deletions clang/include/clang/AST/OperationKinds.def
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Expand Up @@ -121,6 +121,7 @@ CAST_OPERATION(FunctionToPointerDecay)
/// CK_NullToPointer - Null pointer constant to pointer, ObjC
/// pointer, or block pointer.
/// (void*) 0
/// (void*) nullptr
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@efriedma-quic efriedma-quic Apr 25, 2025

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(Copy-pasting comment since I accidentally put it on the commit, instead of on the review.)

That's not helpful? The issue isn't that the operand is a nullptr constant; the issue is that the result is a nullptr constant. Something like (std::nullptr_t)x.

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@alexfh alexfh Apr 25, 2025

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Sorry, I misunderstood your previous comment. Now, is (std::nullptr_t)x what you'd like to see in that comment verbatim?

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@rjmccall rjmccall Apr 25, 2025 •
edited
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I think Eli is asking for you to note in the text that the result of this conversion can still be a null pointer constant if it has type std::nullptr_t. While the conversion does always produce null pointer values, it does not otherwise produce null pointer constants as defined by the C++ standard. Only integer literal 0 and pr-values of type std::nullptr_t are null pointer constants.

I don't think we should have (std::nullptr_t) x in the list of examples because that is not generally valid C++; only (std::nullptr_t) 0 is valid.

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@alexfh alexfh Apr 25, 2025

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Okay, hopefully, I got it right this time.

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@alexfh alexfh Apr 28, 2025

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@efriedma-quic I'll land the fix now. Please let me know, if the comment on CK_NullToPointer needs to be revised.

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@efriedma-quic efriedma-quic Apr 28, 2025

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Maybe we can simplify it to just:

/// CK_NullToPointer - Null pointer constant to pointer, ObjC
/// pointer, block pointer, or std::nullptr_t.

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@alexfh alexfh Apr 28, 2025

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Sure. Done in b509f7c.

/// void (^block)() = 0;
CAST_OPERATION(NullToPointer)

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6 changes: 4 additions & 2 deletions clang/lib/CodeGen/CodeGenTypes.cpp
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Expand Up @@ -850,12 +850,14 @@ CodeGenTypes::getCGRecordLayout(const RecordDecl *RD) {
}

bool CodeGenTypes::isPointerZeroInitializable(QualType T) {
assert((T->isAnyPointerType() || T->isBlockPointerType()) && "Invalid type");
assert((T->isAnyPointerType() || T->isBlockPointerType() ||
T->isNullPtrType()) &&
"Invalid type");
return isZeroInitializable(T);
}

bool CodeGenTypes::isZeroInitializable(QualType T) {
if (T->getAs<PointerType>())
if (T->getAs<PointerType>() || T->isNullPtrType())
return Context.getTargetNullPointerValue(T) == 0;

if (const auto *AT = Context.getAsArrayType(T)) {
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7 changes: 7 additions & 0 deletions clang/test/CodeGenCXX/nullptr.cpp
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Expand Up @@ -70,3 +70,10 @@ namespace PR39528 {
void f(nullptr_t);
void g() { f(null); }
}

// CHECK-LABEL: define {{.*}}pr137276
// CHECK: {{^}} store i64 0, ptr %arr, align 8{{$}}
void pr137276(nullptr_t np, int i) {
long arr[] = { long(np), i, 0 };
(void)arr;
}
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