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[X86] Allow using the lzcnt intrinsics for non-LZCNT targets #128284

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Merged
merged 2 commits into from
Feb 22, 2025
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[X86] Allow using the lzcnt intrinsics for non-LZCNT targets #128284

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[X86] Allow using the lzcnt intrinsics for non-LZCNT targets
phoebewang Feb 22, 2025
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phoebewang Feb 22, 2025
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7 changes: 2 additions & 5 deletions clang/include/clang/Basic/BuiltinsX86.td
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Original file line number Diff line number Diff line change
Expand Up @@ -832,18 +832,15 @@ let Features = "rdseed", Attributes = [NoThrow] in {
def rdseed32_step : X86Builtin<"unsigned int(unsigned int *)">;
}

let Features = "lzcnt", Attributes = [NoThrow, Const, Constexpr] in {
def lzcnt_u16 : X86Builtin<"unsigned short(unsigned short)">;
def lzcnt_u32 : X86Builtin<"unsigned int(unsigned int)">;
}

let Features = "bmi", Attributes = [NoThrow, Const, Constexpr] in {
def bextr_u32 : X86Builtin<"unsigned int(unsigned int, unsigned int)">;
}

let Attributes = [NoThrow, Const, Constexpr] in {
def tzcnt_u16 : X86Builtin<"unsigned short(unsigned short)">;
def tzcnt_u32 : X86Builtin<"unsigned int(unsigned int)">;
def lzcnt_u16 : X86Builtin<"unsigned short(unsigned short)">;
def lzcnt_u32 : X86Builtin<"unsigned int(unsigned int)">;
}

let Features = "bmi2", Attributes = [NoThrow, Const, Constexpr] in {
Expand Down
5 changes: 1 addition & 4 deletions clang/include/clang/Basic/BuiltinsX86_64.td
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Expand Up @@ -126,16 +126,13 @@ let Features = "rdseed", Attributes = [NoThrow] in {
def rdseed64_step : X86Builtin<"unsigned int(unsigned long long int *)">;
}

let Features = "lzcnt", Attributes = [NoThrow, Const, Constexpr] in {
def lzcnt_u64 : X86Builtin<"unsigned long long int(unsigned long long int)">;
}

let Features = "bmi", Attributes = [NoThrow, Const, Constexpr] in {
def bextr_u64 : X86Builtin<"unsigned long long int(unsigned long long int, unsigned long long int)">;
}

let Attributes = [NoThrow, Const, Constexpr] in {
def tzcnt_u64 : X86Builtin<"unsigned long long int(unsigned long long int)">;
def lzcnt_u64 : X86Builtin<"unsigned long long int(unsigned long long int)">;
}

let Features = "bmi2", Attributes = [NoThrow, Const, Constexpr] in {
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5 changes: 2 additions & 3 deletions clang/lib/Headers/lzcntintrin.h
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Expand Up @@ -17,10 +17,9 @@
/* Define the default attributes for the functions in this file. */
#if defined(__cplusplus) && (__cplusplus >= 201103L)
#define __DEFAULT_FN_ATTRS \
__attribute__((__always_inline__, __nodebug__, __target__("lzcnt"))) constexpr
__attribute__((__always_inline__, __nodebug__)) constexpr
#else
#define __DEFAULT_FN_ATTRS \
__attribute__((__always_inline__, __nodebug__, __target__("lzcnt")))
#define __DEFAULT_FN_ATTRS __attribute__((__always_inline__, __nodebug__))
#endif

#ifndef _MSC_VER
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6 changes: 3 additions & 3 deletions clang/test/CodeGen/X86/lzcnt-builtins.c
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@@ -1,5 +1,5 @@
// RUN: %clang_cc1 -x c -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +lzcnt -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -x c++ -std=c++11 -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +lzcnt -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -x c -ffreestanding %s -triple=x86_64-apple-darwin -emit-llvm -o - | FileCheck %s
// RUN: %clang_cc1 -x c++ -std=c++11 -ffreestanding %s -triple=x86_64-apple-darwin -emit-llvm -o - | FileCheck %s


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@RKSimon RKSimon Feb 22, 2025

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Add a comment explaining that these will lower correctly with/without lzcnt

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@phoebewang phoebewang Feb 22, 2025

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Added in lzcntintrin.h

#include <immintrin.h>
Expand Down Expand Up @@ -56,4 +56,4 @@ char lzcntu32_2[_lzcnt_u32(0x00000010) == 27 ? 1 : -1];
char lzcntu64_0[_lzcnt_u64(0x0000000000000000ULL) == 64 ? 1 : -1];
char lzcntu64_1[_lzcnt_u64(0x8000000000000000ULL) == 0 ? 1 : -1];
char lzcntu64_2[_lzcnt_u64(0x0000000100000000ULL) == 31 ? 1 : -1];
#endif
#endif