[clang] [Clang] Fix atomic boolean compound assignment (#33210) (PR #178220)

[via cfe-commits]

https://github.com/kiran-isaac updated https://github.com/llvm/llvm-project/pull/178220

>From f1583f9e09febf7b3c2d9cec69df52514b30cd41 Mon Sep 17 00:00:00 2001
From: Kiran Sturt <kiran.sturt at arm.com>
Date: Tue, 30 Dec 2025 18:05:53 +0000
Subject: [PATCH 1/3] [Clang] Fix atomic boolean compound assignment (#33210)

---
 clang/lib/CodeGen/CGExprScalar.cpp            |  7 ++++
 .../CodeGen/compound-assign-atomic-bool.c     | 33 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 clang/test/CodeGen/compound-assign-atomic-bool.c

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 11af497390671..0d92be12959a9 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1591,6 +1591,13 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
   if (DstType->isBooleanType())
     return EmitConversionToBool(Src, SrcType);
 
+  // Also handle conversions to atomic bools
+  if (const AtomicType *atomicType = DstType->getAs<AtomicType>()) {
+    QualType ValueType = atomicType->getValueType();
+    if (ValueType->isBooleanType())
+      return EmitConversionToBool(Src, ValueType);
+  }
+
   llvm::Type *DstTy = ConvertType(DstType);
 
   // Cast from half through float if half isn't a native type.
diff --git a/clang/test/CodeGen/compound-assign-atomic-bool.c b/clang/test/CodeGen/compound-assign-atomic-bool.c
new file mode 100644
index 0000000000000..8a39a76788e66
--- /dev/null
+++ b/clang/test/CodeGen/compound-assign-atomic-bool.c
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+
+// When performing compound assignment on atomic_bool, ensure that we
+// correctly handle the conversion from integer to boolean, by comparing
+// with zero rather than truncating.
+
+#include <stdatomic.h>
+#include <stdbool.h>
+
+
+// CHECK: @compund_assign_add
+int compund_assign_add(void) {
+    atomic_bool b;
+
+    b += 2;
+    // CHECK: add
+    // CHECK-NEXT: icmp ne
+    // CHECK-NEXT: zext
+    // CHECK-NEXT: cmpxchg
+    return b;
+}
+
+// CHECK: @compund_assign_minus
+int compund_assign_minus(void) {
+    atomic_bool b;
+
+    b -= 2;
+    // CHECK: sub
+    // CHECK-NEXT: icmp ne
+    // CHECK-NEXT: zext
+    // CHECK-NEXT: cmpxchg
+    return b;
+}

>From f015dde439add64eaa0fd2cc168ac1c8de3b4866 Mon Sep 17 00:00:00 2001
From: Kiran Sturt <kiran.sturt at arm.com>
Date: Thu, 5 Feb 2026 15:54:56 +0000
Subject: [PATCH 2/3] Style changes, add release notes

Change-Id: I98669a9543f0c93a08fa939655ebd12a2f321ae5
---
 clang/docs/ReleaseNotes.rst                      | 3 +++
 clang/lib/CodeGen/CGExprScalar.cpp               | 4 ++--
 clang/test/CodeGen/compound-assign-atomic-bool.c | 8 ++------
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 4d2ff6e6e4e40..4be4607a528c9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -195,6 +195,9 @@ Improvements to Coverage Mapping
 
 Bug Fixes in This Version
 -------------------------
+
+- Fixed atomic boolean compound assignment; the conversion back to atomic bool would be miscompiled. (#GH33210)
+
 - Fixed a failed assertion in the preprocessor when ``__has_embed`` parameters are missing parentheses. (#GH175088)
 
 - Fix lifetime extension of temporaries in for-range-initializers in templates. (#GH165182)
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 0d92be12959a9..86fa740908f75 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1592,8 +1592,8 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
     return EmitConversionToBool(Src, SrcType);
 
   // Also handle conversions to atomic bools
-  if (const AtomicType *atomicType = DstType->getAs<AtomicType>()) {
-    QualType ValueType = atomicType->getValueType();
+  if (const auto *DstAsAtomic = DstType->getAs<AtomicType>()) {
+    QualType ValueType = DstAsAtomic->getValueType();
     if (ValueType->isBooleanType())
       return EmitConversionToBool(Src, ValueType);
   }
diff --git a/clang/test/CodeGen/compound-assign-atomic-bool.c b/clang/test/CodeGen/compound-assign-atomic-bool.c
index 8a39a76788e66..4e8f351b49b81 100644
--- a/clang/test/CodeGen/compound-assign-atomic-bool.c
+++ b/clang/test/CodeGen/compound-assign-atomic-bool.c
@@ -4,13 +4,9 @@
 // correctly handle the conversion from integer to boolean, by comparing
 // with zero rather than truncating.
 
-#include <stdatomic.h>
-#include <stdbool.h>
-
-
 // CHECK: @compund_assign_add
 int compund_assign_add(void) {
-    atomic_bool b;
+    _Atomic _Bool b;
 
     b += 2;
     // CHECK: add
@@ -22,7 +18,7 @@ int compund_assign_add(void) {
 
 // CHECK: @compund_assign_minus
 int compund_assign_minus(void) {
-    atomic_bool b;
+    _Atomic _Bool b;
 
     b -= 2;
     // CHECK: sub

>From da62e75d4ed297ec243b51c12ea4b89b4404093a Mon Sep 17 00:00:00 2001
From: Kiran Sturt <kiran.sturt at arm.com>
Date: Thu, 5 Feb 2026 16:15:52 +0000
Subject: [PATCH 3/3] Lift the conversion from EmitScalerConversion to
 EmitCompoundAssignLValue.

Atomics aren't really scaler, are they.

Change-Id: Ida3cc76eecde6b426c0f29ac52034b89b45f6816
---
 clang/lib/CodeGen/CGExprScalar.cpp | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 86fa740908f75..20c5475f32a9a 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1591,13 +1591,6 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
   if (DstType->isBooleanType())
     return EmitConversionToBool(Src, SrcType);
 
-  // Also handle conversions to atomic bools
-  if (const auto *DstAsAtomic = DstType->getAs<AtomicType>()) {
-    QualType ValueType = DstAsAtomic->getValueType();
-    if (ValueType->isBooleanType())
-      return EmitConversionToBool(Src, ValueType);
-  }
-
   llvm::Type *DstTy = ConvertType(DstType);
 
   // Cast from half through float if half isn't a native type.
@@ -4045,10 +4038,15 @@ LValue ScalarExprEmitter::EmitCompoundAssignLValue(
   if (LHSLV.isBitField()) {
     Previous = Result;
     Result = EmitScalarConversion(Result, PromotionTypeCR, LHSTy, Loc);
-  } else
+  } else if (const auto *atomicTy = LHSTy->getAs<AtomicType>()) {
+    Result = EmitScalarConversion(Result, PromotionTypeCR,
+                                  atomicTy->getValueType(), Loc,
+                                  ScalarConversionOpts(CGF.SanOpts));
+  } else {
     Result = EmitScalarConversion(Result, PromotionTypeCR, LHSTy, Loc,
                                   ScalarConversionOpts(CGF.SanOpts));
-
+  }
+  
   if (atomicPHI) {
     llvm::BasicBlock *curBlock = Builder.GetInsertBlock();
     llvm::BasicBlock *contBB = CGF.createBasicBlock("atomic_cont", CGF.CurFn);