[Clang] Fix clang to emit llvm-ir for fadd/fsub atomics

[Amichaxx]

Currently, Clang emits CAS loops for atomic fp compound assignments, instead of atomicrmw instructions. The code in CGExprScalar.cpp now checks for both integer and floating-point atomic types and emits atomicrmw fadd/fsub instructions in the LLVM IR.

cc: @efriedma-quic ?

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Amina Chabane (Amichaxx)

Changes

Currently, Clang emits CAS loops for atomic fp compound assignments, instead of atomicrmw instructions. The code in CGExprScalar.cpp now checks for both integer and floating-point atomic types and emits atomicrmw fadd/fsub instructions in the LLVM IR.

cc: @efriedma-quic ?

---

Full diff: https://github.com/llvm/llvm-project/pull/162679.diff

2 Files Affected:

• (modified) clang/lib/CodeGen/CGExprScalar.cpp (+16-5)
• (added) clang/test/CodeGen/aarch64-lsfe-atomics.c (+61)

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index f319b176513f8..4028a91ad7639 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -3847,7 +3847,16 @@ LValue ScalarExprEmitter::EmitCompoundAssignLValue(
   llvm::PHINode *atomicPHI = nullptr;
   if (const AtomicType *atomicTy = LHSTy->getAs<AtomicType>()) {
     QualType type = atomicTy->getValueType();
-    if (!type->isBooleanType() && type->isIntegerType() &&
+    const bool isFloat = type->isFloatingType();
+    const bool isInteger = type->isIntegerType();
+
+    bool isPowerOfTwo = false;
+    if (isFloat || isInteger) {
+      llvm::Type *IRTy = CGF.ConvertType(type);
+      uint64_t StoreBits = CGF.CGM.getDataLayout().getTypeStoreSizeInBits(IRTy);
+      isPowerOfTwo = llvm::isPowerOf2_64(StoreBits);
+    }
+    if (!type->isBooleanType() && (isInteger || isFloat) && isPowerOfTwo &&
         !(type->isUnsignedIntegerType() &&
           CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow)) &&
         CGF.getLangOpts().getSignedOverflowBehavior() !=
@@ -3862,12 +3871,14 @@ LValue ScalarExprEmitter::EmitCompoundAssignLValue(
         case BO_ShrAssign:
           break;
         case BO_AddAssign:
-          AtomicOp = llvm::AtomicRMWInst::Add;
-          Op = llvm::Instruction::Add;
+          AtomicOp =
+              isFloat ? llvm::AtomicRMWInst::FAdd : llvm::AtomicRMWInst::Add;
+          Op = isFloat ? llvm::Instruction::FAdd : llvm::Instruction::Add;
           break;
         case BO_SubAssign:
-          AtomicOp = llvm::AtomicRMWInst::Sub;
-          Op = llvm::Instruction::Sub;
+          AtomicOp =
+              isFloat ? llvm::AtomicRMWInst::FSub : llvm::AtomicRMWInst::Sub;
+          Op = isFloat ? llvm::Instruction::FSub : llvm::Instruction::Sub;
           break;
         case BO_AndAssign:
           AtomicOp = llvm::AtomicRMWInst::And;
diff --git a/clang/test/CodeGen/aarch64-lsfe-atomics.c b/clang/test/CodeGen/aarch64-lsfe-atomics.c
new file mode 100644
index 0000000000000..957e960b3fe3a
--- /dev/null
+++ b/clang/test/CodeGen/aarch64-lsfe-atomics.c
@@ -0,0 +1,61 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 6
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple=aarch64-linux-gnu | FileCheck %s --check-prefix=CHECK-LLVM
+
+_Atomic(float) f;
+_Atomic(double) d;
+
+// CHECK-LLVM-LABEL: define dso_local void @test_float_add(
+// CHECK-LLVM-SAME: float noundef [[VAL:%.*]]) #[[ATTR0:[0-9]+]] {
+// CHECK-LLVM-NEXT:  [[ENTRY:.*:]]
+// CHECK-LLVM-NEXT:    [[VAL_ADDR:%.*]] = alloca float, align 4
+// CHECK-LLVM-NEXT:    store float [[VAL]], ptr [[VAL_ADDR]], align 4
+// CHECK-LLVM-NEXT:    [[TMP0:%.*]] = load float, ptr [[VAL_ADDR]], align 4
+// CHECK-LLVM-NEXT:    [[TMP1:%.*]] = atomicrmw fadd ptr @f, float [[TMP0]] seq_cst, align 4
+// CHECK-LLVM-NEXT:    [[TMP2:%.*]] = fadd float [[TMP1]], [[TMP0]]
+// CHECK-LLVM-NEXT:    ret void
+//
+void test_float_add(float val) {
+  f += val;
+}
+
+// CHECK-LLVM-LABEL: define dso_local void @test_double_add(
+// CHECK-LLVM-SAME: double noundef [[VAL:%.*]]) #[[ATTR0]] {
+// CHECK-LLVM-NEXT:  [[ENTRY:.*:]]
+// CHECK-LLVM-NEXT:    [[VAL_ADDR:%.*]] = alloca double, align 8
+// CHECK-LLVM-NEXT:    store double [[VAL]], ptr [[VAL_ADDR]], align 8
+// CHECK-LLVM-NEXT:    [[TMP0:%.*]] = load double, ptr [[VAL_ADDR]], align 8
+// CHECK-LLVM-NEXT:    [[TMP1:%.*]] = atomicrmw fadd ptr @d, double [[TMP0]] seq_cst, align 8
+// CHECK-LLVM-NEXT:    [[TMP2:%.*]] = fadd double [[TMP1]], [[TMP0]]
+// CHECK-LLVM-NEXT:    ret void
+//
+void test_double_add(double val) {
+  d += val;
+}
+
+// CHECK-LLVM-LABEL: define dso_local void @test_float_sub(
+// CHECK-LLVM-SAME: float noundef [[VAL:%.*]]) #[[ATTR0]] {
+// CHECK-LLVM-NEXT:  [[ENTRY:.*:]]
+// CHECK-LLVM-NEXT:    [[VAL_ADDR:%.*]] = alloca float, align 4
+// CHECK-LLVM-NEXT:    store float [[VAL]], ptr [[VAL_ADDR]], align 4
+// CHECK-LLVM-NEXT:    [[TMP0:%.*]] = load float, ptr [[VAL_ADDR]], align 4
+// CHECK-LLVM-NEXT:    [[TMP1:%.*]] = atomicrmw fsub ptr @f, float [[TMP0]] seq_cst, align 4
+// CHECK-LLVM-NEXT:    [[TMP2:%.*]] = fsub float [[TMP1]], [[TMP0]]
+// CHECK-LLVM-NEXT:    ret void
+//
+void test_float_sub(float val) {
+  f -= val;
+}
+
+// CHECK-LLVM-LABEL: define dso_local void @test_double_sub(
+// CHECK-LLVM-SAME: double noundef [[VAL:%.*]]) #[[ATTR0]] {
+// CHECK-LLVM-NEXT:  [[ENTRY:.*:]]
+// CHECK-LLVM-NEXT:    [[VAL_ADDR:%.*]] = alloca double, align 8
+// CHECK-LLVM-NEXT:    store double [[VAL]], ptr [[VAL_ADDR]], align 8
+// CHECK-LLVM-NEXT:    [[TMP0:%.*]] = load double, ptr [[VAL_ADDR]], align 8
+// CHECK-LLVM-NEXT:    [[TMP1:%.*]] = atomicrmw fsub ptr @d, double [[TMP0]] seq_cst, align 8
+// CHECK-LLVM-NEXT:    [[TMP2:%.*]] = fsub double [[TMP1]], [[TMP0]]
+// CHECK-LLVM-NEXT:    ret void
+//
+void test_double_sub(double val){
+    d -= val;
+}