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[Clang][CodeGen] Use EmitLoadOfLValue instead of EmitLoadOfScalar to get LHS for complex compound assignment #166798

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Merged
merged 10 commits into from
Nov 19, 2025
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Merged

[Clang][CodeGen] Use EmitLoadOfLValue instead of EmitLoadOfScalar to get LHS for complex compound assignment #166798

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eab7dd0
[Clang][CodeGen] Use EmitLoadOfLValue instead of EmitLoadOfScalar to …
BStott6 Nov 6, 2025
abcef13
Merge branch 'llvm:main' into fix-166512
BStott6 Nov 6, 2025
ab4e0ee
Replace EmitStoreOfScalar with EmitStoreThroughLValue too
BStott6 Nov 7, 2025
5a203e6
Introduce test for fixed crash
BStott6 Nov 10, 2025
6ca51cd
Add test for correct codegen
BStott6 Nov 11, 2025
1232acd
Add release note for fix
BStott6 Nov 11, 2025
76b16c9
Clarify test
BStott6 Nov 12, 2025
03d0c67
Remove UBSan complex bitfield crash test
BStott6 Nov 18, 2025
3cb3f71
Merge branch 'main' into fix-166512
BStott6 Nov 19, 2025
c85dc55
Specify triple for codegen test
BStott6 Nov 19, 2025
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1 change: 1 addition & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -478,6 +478,7 @@ Bug Fixes in This Version
- Fixed a failed assertion with empty filename in ``#embed`` directive. (#GH162951)
- Fixed a crash triggered by unterminated ``__has_embed``. (#GH162953)
- Accept empty enumerations in MSVC-compatible C mode. (#GH114402)
- Fix a bug leading to incorrect code generation with complex number compound assignment and bitfield values, which also caused a crash with UBsan. (#GH166798)
- Fixed false-positive shadow diagnostics for lambdas in explicit object member functions. (#GH163731)

Bug Fixes to Compiler Builtins
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4 changes: 2 additions & 2 deletions clang/lib/CodeGen/CGExprComplex.cpp
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Expand Up @@ -1283,7 +1283,7 @@ EmitCompoundAssignLValue(const CompoundAssignOperator *E,
else
OpInfo.LHS = EmitComplexToComplexCast(LHSVal, LHSTy, OpInfo.Ty, Loc);
} else {
llvm::Value *LHSVal = CGF.EmitLoadOfScalar(LHS, Loc);
llvm::Value *LHSVal = CGF.EmitLoadOfLValue(LHS, Loc).getScalarVal();
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@efriedma-quic efriedma-quic Nov 6, 2025

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Do we also need to change the call to EmitStoreOfScalar?

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@BStott6 BStott6 Nov 7, 2025

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I'll look into it

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@BStott6 BStott6 Nov 7, 2025

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I think it does make sense to replace it with EmitStoreThroughLValue, what do you think?

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@efriedma-quic efriedma-quic Nov 7, 2025

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That seems fine.

// For floating point real operands we can directly pass the scalar form
// to the binary operator emission and potentially get more efficient code.
if (LHSTy->isRealFloatingType()) {
Expand Down Expand Up @@ -1318,7 +1318,7 @@ EmitCompoundAssignLValue(const CompoundAssignOperator *E,
} else {
llvm::Value *ResVal =
CGF.EmitComplexToScalarConversion(Result, OpInfo.Ty, LHSTy, Loc);
CGF.EmitStoreOfScalar(ResVal, LHS, /*isInit*/ false);
CGF.EmitStoreThroughLValue(RValue::get(ResVal), LHS, /*isInit*/ false);
Val = RValue::get(ResVal);
}

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25 changes: 25 additions & 0 deletions clang/test/CodeGen/complex-compound-assign-bitfield.c
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@@ -0,0 +1,25 @@
// RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -std=c23 -emit-llvm -o - | FileCheck %s

struct Bits {
int pad1: 30;
bool b: 1;
int pad2: 1;
};

int main(void) {
// CHECK-LABEL: define dso_local i32 @main() #0 {
struct Bits x;
x.b += __builtin_complex(-1.0f, 0.0f);
// CHECK: %bf.load = load i32, ptr %x, align 4
// CHECK-NEXT: %bf.lshr = lshr i32 %bf.load, 30
// CHECK-NEXT: %bf.clear = and i32 %bf.lshr, 1
// CHECK-NEXT: %bf.cast = trunc i32 %bf.clear to i1
// CHECK-NEXT: %conv = uitofp i1 %bf.cast to float

// CHECK: %0 = zext i1 %tobool1 to i32
// CHECK-NEXT: %bf.load2 = load i32, ptr %x, align 4
// CHECK-NEXT: %bf.shl = shl i32 %0, 30
// CHECK-NEXT: %bf.clear3 = and i32 %bf.load2, -1073741825
// CHECK-NEXT: %bf.set = or i32 %bf.clear3, %bf.shl
// CHECK-NEXT: store i32 %bf.set, ptr %x, align 4
}