[clang] 34f59d7 - [Clang][ARM] Fix __ARM_FEATURE_LDREX on Armv8-M (#149538)

[via cfe-commits]

Author: Simon Tatham
Date: 2025-07-22T08:53:45+01:00
New Revision: 34f59d79209268eca9c63ccc7646128f2dc52fe3

URL: https://github.com/llvm/llvm-project/commit/34f59d79209268eca9c63ccc7646128f2dc52fe3
DIFF: https://github.com/llvm/llvm-project/commit/34f59d79209268eca9c63ccc7646128f2dc52fe3.diff

LOG: [Clang][ARM] Fix __ARM_FEATURE_LDREX on Armv8-M (#149538)

The Armv8-M architecture doesn't have the LDREXD and STREXD
instructions, for exclusive load/store of a 64-bit quantity split across
two registers. But the `__ARM_FEATURE_LDREX` macro was set to a value
that claims it does, because the case for Armv8 was missing a check for
M profile.

The Armv7 case got it right, so I've just made the two cases the same.

Added: 
    

Modified: 
    clang/lib/Basic/Targets/ARM.cpp
    clang/test/Preprocessor/arm-acle-6.4.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/Basic/Targets/ARM.cpp b/clang/lib/Basic/Targets/ARM.cpp
index 7ff8e51f8a7f8..29de34bbc4fe4 100644
--- a/clang/lib/Basic/Targets/ARM.cpp
+++ b/clang/lib/Basic/Targets/ARM.cpp
@@ -623,13 +623,15 @@ bool ARMTargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       LDREX = LDREX_W;
     break;
   case 7:
+  case 8:
     if (ArchProfile == llvm::ARM::ProfileKind::M)
       LDREX = LDREX_W | LDREX_H | LDREX_B;
     else
       LDREX = LDREX_D | LDREX_W | LDREX_H | LDREX_B;
     break;
-  case 8:
   case 9:
+    assert(ArchProfile != llvm::ARM::ProfileKind::M &&
+           "No Armv9-M architectures defined");
     LDREX = LDREX_D | LDREX_W | LDREX_H | LDREX_B;
   }
 

diff  --git a/clang/test/Preprocessor/arm-acle-6.4.c b/clang/test/Preprocessor/arm-acle-6.4.c
index 2c8f4868263a6..48deba74c8ab2 100644
--- a/clang/test/Preprocessor/arm-acle-6.4.c
+++ b/clang/test/Preprocessor/arm-acle-6.4.c
@@ -188,6 +188,37 @@
 // RUN: %clang --target=arm-arm-none-eabi -mcpu=cortex-m33 -x c -E -dM %s -o - | FileCheck %s -check-prefix CHECK-M-DSP
 // RUN: %clang --target=arm-arm-none-eabi -march=armv8m.main+dsp -x c -E -dM %s -o - | FileCheck %s -check-prefix CHECK-M-DSP
 
+// RUN: %clang -target arm-none-linux-eabi -march=armv8m.base -x c -E -dM %s -o - | FileCheck %s -check-prefix CHECK-V8M-BASE
+
+// CHECK-V8M-BASE-NOT: __ARM_ARCH_ISA_ARM
+// CHECK-V8M-BASE-NOT: __ARM_FEATURE_DSP
+// CHECK-V8M-BASE-NOT: __ARM_FEATURE_SIMD32
+// CHECK-V8M-BASE:     __ARM_ARCH 8
+// CHECK-V8M-BASE:     __ARM_ARCH_ISA_THUMB 1
+// CHECK-V8M-BASE:     __ARM_ARCH_PROFILE 'M'
+// CHECK-V8M-BASE:     __ARM_FEATURE_CLZ 1
+// CHECK-V8M-BASE:     __ARM_FEATURE_IDIV 1
+// CHECK-V8M-BASE:     __ARM_FEATURE_LDREX 0x7
+// CHECK-V8M-BASE:     __ARM_FEATURE_QBIT 1
+// CHECK-V8M-BASE:     __ARM_FEATURE_SAT
+// CHECK-V8M-BASE-NOT: __ARM_FEATURE_UNALIGNED
+
+// RUN: %clang -target arm-none-linux-eabi -march=armv8m.main -x c -E -dM %s -o - | FileCheck %s -check-prefix CHECK-V8M-MAIN
+// RUN: %clang -target arm-none-linux-eabi -march=armv8.1m.main -x c -E -dM %s -o - | FileCheck %s -check-prefix CHECK-V8M-MAIN
+
+// CHECK-V8M-MAIN-NOT: __ARM_ARCH_ISA_ARM
+// CHECK-V8M-MAIN-NOT: __ARM_FEATURE_DSP
+// CHECK-V8M-MAIN-NOT: __ARM_FEATURE_SIMD32
+// CHECK-V8M-MAIN:     __ARM_ARCH 8
+// CHECK-V8M-MAIN:     __ARM_ARCH_ISA_THUMB 2
+// CHECK-V8M-MAIN:     __ARM_ARCH_PROFILE 'M'
+// CHECK-V8M-MAIN:     __ARM_FEATURE_CLZ 1
+// CHECK-V8M-MAIN:     __ARM_FEATURE_IDIV 1
+// CHECK-V8M-MAIN:     __ARM_FEATURE_LDREX 0x7
+// CHECK-V8M-MAIN:     __ARM_FEATURE_QBIT 1
+// CHECK-V8M-MAIN:     __ARM_FEATURE_SAT 1
+// CHECK-V8M-MAIN:     __ARM_FEATURE_UNALIGNED 1
+
 // CHECK-M-DSP: __ARM_FEATURE_DSP 1
 // CHECK-M-DSP: __ARM_FEATURE_SIMD32 1