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update clz/ctz for BMI1

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Daan Leijen 2025-02-28 16:26:45 -08:00
parent b4d2c54696
commit c3fc75e0ff
1 changed files with 8 additions and 4 deletions
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12
include/mimalloc/bits.h
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@ -195,7 +195,11 @@ size_t _mi_clz_generic(size_t x);
size_t _mi_ctz_generic(size_t x);
static inline size_t mi_ctz(size_t x) {
#if defined(__GNUC__) && MI_ARCH_X64
#if defined(__GNUC__) && MI_ARCH_X64 && defined(__BMI1__)
size_t r;
__asm ("tzcnt\t%1, %0" : "=r"(r) : "r"(x) : "cc");
return r;
#elif defined(__GNUC__) && MI_ARCH_X64
// tzcnt is interpreted as bsf if BMI1 is not supported (pre-haswell)
// if the argument is zero:
// - tzcnt: sets carry-flag, and returns MI_SIZE_BITS
@ -226,7 +230,7 @@ static inline size_t mi_ctz(size_t x) {
static inline size_t mi_clz(size_t x) {
// we don't optimize anymore to lzcnt as there are still non BMI1 cpu's around (like Intel Celeron, see issue #1016)
// on pre-haswell cpu's lzcnt gets executed as bsr which is not equivalent (at it returns the bit position)
#if 0 && defined(__GNUC__) && MI_ARCH_X64 && defined(__BMI1__) // on x64 lzcnt is defined for 0
#if defined(__GNUC__) && MI_ARCH_X64 && defined(__BMI1__) // on x64 lzcnt is defined for 0
size_t r;
__asm ("lzcnt\t%1, %0" : "=r"(r) : "r"(x) : "cc");
return r;
@ -259,7 +263,7 @@ static inline size_t mi_clz(size_t x) {
// with the `idx` is set to the bit index (`0 <= *idx < MI_BFIELD_BITS`).
static inline bool mi_bsf(size_t x, size_t* idx) {
// we don't optimize anymore to lzcnt so we run correctly on older cpu's as well
#if 0 && defined(__GNUC__) && MI_ARCH_X64 && defined(__BMI1__) && (!defined(__clang_major__) || __clang_major__ >= 9)
#if defined(__GNUC__) && MI_ARCH_X64 && defined(__BMI1__) && (!defined(__clang_major__) || __clang_major__ >= 9)
// on x64 the carry flag is set on zero which gives better codegen
bool is_zero;
__asm ( "tzcnt\t%2, %1" : "=@ccc"(is_zero), "=r"(*idx) : "r"(x) : "cc" );
@ -276,7 +280,7 @@ static inline bool mi_bsf(size_t x, size_t* idx) {
// return false if `x==0` (with `*idx` undefined) and true otherwise,
// with the `idx` is set to the bit index (`0 <= *idx < MI_BFIELD_BITS`).
static inline bool mi_bsr(size_t x, size_t* idx) {
#if 0 && defined(_MSC_VER) && (MI_ARCH_X64 || MI_ARCH_X86 || MI_ARCH_ARM64 || MI_ARCH_ARM32)
#if defined(_MSC_VER) && (MI_ARCH_X64 || MI_ARCH_X86 || MI_ARCH_ARM64 || MI_ARCH_ARM32)
unsigned long i;
return (mi_msc_builtinz(_BitScanReverse)(&i, x) ? (*idx = (size_t)i, true) : false);
#else