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Apr 29, 2025
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[ARM][Driver] Ensure NEON is enabled and disabled correctly #137595

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[ARM][Driver] Ensure NEON is enabled and Disabled correctly
Stylie777 Apr 25, 2025
19f6d04
Formatting fixes
Stylie777 Apr 28, 2025
ab34913
Updates after review comments.
Stylie777 Apr 28, 2025
2bb9077
Change disabling features to use .insert rather than a for loop
Stylie777 Apr 28, 2025
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2 changes: 2 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Expand Up @@ -601,6 +601,8 @@ Arm and AArch64 Support
- The ``+nosimd`` attribute is now fully supported for ARM. Previously, this had no effect when being used with
ARM targets, however this will now disable NEON instructions being generated. The ``simd`` option is
also now printed when the ``--print-supported-extensions`` option is used.
- NEON is correctly enabled when using features that depend on NEON , and disables all features that depend on
NEON when using ``+nosimd``.

- Support for __ptrauth type qualifier has been added.

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51 changes: 47 additions & 4 deletions clang/lib/Driver/ToolChains/Arch/ARM.cpp
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Expand Up @@ -781,6 +781,30 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
if (FPUKind == llvm::ARM::FK_FPV5_D16 || FPUKind == llvm::ARM::FK_FPV5_SP_D16)
Features.push_back("-mve.fp");

// If SIMD has been disabled and the selected FPU support NEON, then features
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"support" → "supports"

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done

// that rely on NEON Instructions should also be disabled. Cases where NEON
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"Instructions" -> "instructions"

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done

// needs activating to support another feature is handled below with the
// crypto feature.
bool HasSimd = false;
const auto ItSimd =
llvm::find_if(llvm::reverse(Features),
[](const StringRef F) { return F.contains("neon"); });
const bool FoundSimd = ItSimd != Features.rend();
const bool FPUSupportsNeon = (llvm::ARM::FPUNames[FPUKind].NeonSupport ==
llvm::ARM::NeonSupportLevel::Neon) ||
(llvm::ARM::FPUNames[FPUKind].NeonSupport ==
llvm::ARM::NeonSupportLevel::Crypto);
if (FoundSimd)
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Replace FoundSimd condition-check with ItSimd != Features.rend() The variable is redundant.

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Done

HasSimd = ItSimd->take_front() == "+";
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The function that should be used here is starts_with("+") and not take_front()
Even though the existing code below:
HasSHA2 = ItSHA2->take_front() == "+"; already use take_front(). I think it might be better to change all, including existing one, to starts_with

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done

if (!HasSimd && FPUSupportsNeon) {
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Optional:
if (!HasSimd && FPUSupportsNeon)
for (auto &F: {"-sha2","-aes","-crypto","-dotprod","-bf16","-imm8"}) Features.push_back(F);

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I have done this, it is a break from how multiple Features are usually added but it does make a cleaner implementation.

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2nd comment, I have updated this (again) to use Features.insert() as this is used elsewhere in ARM.cpp and removes the need for the for loop and the .insert() function handles this.

Features.push_back("-sha2");
Features.push_back("-aes");
Features.push_back("-crypto");
Features.push_back("-dotprod");
Features.push_back("-bf16");
Features.push_back("-imm8");
}

// For Arch >= ARMv8.0 && A or R profile: crypto = sha2 + aes
// Rather than replace within the feature vector, determine whether each
// algorithm is enabled and append this to the end of the vector.
Expand All @@ -791,6 +815,9 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
// FIXME: this needs reimplementation after the TargetParser rewrite
bool HasSHA2 = false;
bool HasAES = false;
bool HasBF16 = false;
bool HasDotprod = false;
bool HasI8MM = false;
const auto ItCrypto =
llvm::find_if(llvm::reverse(Features), [](const StringRef F) {
return F.contains("crypto");
Expand All @@ -803,12 +830,25 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
llvm::find_if(llvm::reverse(Features), [](const StringRef F) {
return F.contains("crypto") || F.contains("aes");
});
const bool FoundSHA2 = ItSHA2 != Features.rend();
const bool FoundAES = ItAES != Features.rend();
if (FoundSHA2)
const auto ItBF16 =
llvm::find_if(llvm::reverse(Features),
[](const StringRef F) { return F.contains("bf16"); });
const auto ItDotprod =
llvm::find_if(llvm::reverse(Features),
[](const StringRef F) { return F.contains("dotprod"); });
const auto ItI8MM =
llvm::find_if(llvm::reverse(Features),
[](const StringRef F) { return F.contains("i8mm"); });
if (ItSHA2 != Features.rend())
HasSHA2 = ItSHA2->take_front() == "+";
if (FoundAES)
if (ItAES != Features.rend())
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starts_with

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done

HasAES = ItAES->take_front() == "+";
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starts_with

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done

if (ItBF16 != Features.rend())
HasBF16 = ItBF16->take_front() == "+";
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starts_with

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done

if (ItDotprod != Features.rend())
HasDotprod = ItDotprod->take_front() == "+";
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starts_with

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done

if (ItI8MM != Features.rend())
HasI8MM = ItI8MM->take_front() == "+";
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starts_with

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Done

if (ItCrypto != Features.rend()) {
if (HasSHA2 && HasAES)
Features.push_back("+crypto");
Expand All @@ -823,6 +863,9 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
else
Features.push_back("-aes");
}
// If any of these features are enabled, NEON should also be enabled.
if (HasAES || HasSHA2 || HasBF16 || HasDotprod || HasI8MM)
Features.push_back("+neon");

if (HasSHA2 || HasAES) {
StringRef ArchSuffix = arm::getLLVMArchSuffixForARM(
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2 changes: 1 addition & 1 deletion clang/test/Driver/arm-features.c
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Expand Up @@ -74,7 +74,7 @@
// Check +crypto for M and R profiles:
//
// RUN: %clang -target arm-arm-none-eabi -march=armv8-r+crypto -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-CRYPTO-R %s
// CHECK-CRYPTO-R: "-cc1"{{.*}} "-target-cpu" "generic"{{.*}} "-target-feature" "+sha2" "-target-feature" "+aes"
// CHECK-CRYPTO-R: "-cc1"{{.*}} "-target-cpu" "generic"{{.*}} "-target-feature" "+sha2" "-target-feature" "+aes" "-target-feature" "+neon"
// RUN: %clang -target arm-arm-none-eabi -march=armv8-m.base+crypto -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-NOCRYPTO5 %s
// RUN: %clang -target arm-arm-none-eabi -march=armv8-m.main+crypto -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-NOCRYPTO5 %s
// RUN: %clang -target arm-arm-none-eabi -mcpu=cortex-m23+crypto -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-NOCRYPTO5 %s
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4 changes: 2 additions & 2 deletions clang/test/Driver/arm-mfpu.c
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Expand Up @@ -407,7 +407,7 @@
// CHECK-ARM8-ANDROID-FP-DEFAULT-DAG: "-target-feature" "+fp-armv8"
// CHECK-ARM8-ANDROID-FP-DEFAULT-DAG: "-target-feature" "+aes"
// CHECK-ARM8-ANDROID-FP-DEFAULT-DAG: "-target-feature" "+sha2"
// CHECK-ARM8-ANDROID-FP-DEFAULT-NOT: "-target-feature" "+neon"
// CHECK-ARM8-ANDROID-FP-DEFAULT-DAG: "-target-feature" "+neon"

// RUN: %clang -target armv8-linux-android %s -### -c 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-ARM8-ANDROID-DEFAULT %s
Expand All @@ -416,7 +416,7 @@
// CHECK-ARM8-ANDROID-DEFAULT-DAG: "-target-feature" "+fp-armv8"
// CHECK-ARM8-ANDROID-DEFAULT-DAG: "-target-feature" "+aes"
// CHECK-ARM8-ANDROID-DEFAULT-DAG: "-target-feature" "+sha2"
// CHECK-ARM8-ANDROID-DEFAULT-NOT: "-target-feature" "+neon"
// CHECK-ARM8-ANDROID-DEFAULT-DAG: "-target-feature" "+neon"

// RUN: %clang -target armv7-linux-androideabi21 %s -mfpu=vfp3-d16 -### -c 2>&1 \
// RUN: | FileCheck --check-prefix=CHECK-ARM7-ANDROID-FP-D16 %s
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10 changes: 8 additions & 2 deletions clang/test/Preprocessor/arm-target-features.c
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Expand Up @@ -1036,10 +1036,16 @@
// CHECK-SIMD: #define __ARM_NEON_FP 0x6
// CHECK-SIMD: #define __ARM_NEON__ 1

// Check that on AArch32 appropriate targets, +nosimd correctly disables NEON instructions.
// RUN: %clang -target arm-none-eabi -march=armv8-a+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
// Check that on AArch32 appropriate targets, +nosimd correctly disables NEON instructions. All features that rely on NEON should also be disabled.
// RUN: %clang -target arm-none-eabi -march=armv9.6-a+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
// RUN: %clang -target arm-none-eabi -mcpu=cortex-r52+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
// RUN: %clang -target arm-none-eabi -mcpu=cortex-a57+nosimd -mfloat-abi=hard -x c -E -dM -o - %s | FileCheck -check-prefix=CHECK-NOSIMD %s
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_BF16 1
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_BF16_VECTOR_ARITHMETIC 1
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_AES 1
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_CRYPTO 1
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_DOTPROD 1
// CHECK-NOSIMD-NOT: #define __ARM_FEATURE_SHA2 1
// CHECK-NOSIMD-NOT: #define __ARM_NEON 1
// CHECK-NOSIMD-NOT: #define __ARM_NEON_FP 0x6
// CHECK-NOSIMD-NOT: #define __ARM_NEON__ 1
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