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author | Ian Lance Taylor <ian@gcc.gnu.org> | 2018-03-07 14:31:03 +0000 |
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committer | Ian Lance Taylor <ian@gcc.gnu.org> | 2018-03-07 14:31:03 +0000 |
commit | 2dab5d909f20be950c35ab4767ba1e0b64cb6bbc (patch) | |
tree | a2f3871cade9720ac021f8cdb38d3be3270e83be /libgo/runtime/runtime_c.c | |
parent | 6cde8c545b8a300409863c70526189d3f7f659df (diff) | |
download | gcc-2dab5d909f20be950c35ab4767ba1e0b64cb6bbc.zip gcc-2dab5d909f20be950c35ab4767ba1e0b64cb6bbc.tar.gz gcc-2dab5d909f20be950c35ab4767ba1e0b64cb6bbc.tar.bz2 |
runtime: use a fence instruction before rdtsc
This implements the same choices made in the gc runtime, except that
for 32-bit x86 we only use the fence instruction if the processor
supports SSE2.
The code here is hacked up for speed; the gc runtime uses straight
assembler.
Reviewed-on: https://go-review.googlesource.com/97715
From-SVN: r258336
Diffstat (limited to 'libgo/runtime/runtime_c.c')
-rw-r--r-- | libgo/runtime/runtime_c.c | 59 |
1 files changed, 55 insertions, 4 deletions
diff --git a/libgo/runtime/runtime_c.c b/libgo/runtime/runtime_c.c index 88f1adf..c65a7e0 100644 --- a/libgo/runtime/runtime_c.c +++ b/libgo/runtime/runtime_c.c @@ -33,13 +33,47 @@ runtime_atoi(const byte *p, intgo len) return n; } +#if defined(__i386__) || defined(__x86_64__) || defined (__s390__) || defined (__s390x__) + +// When cputicks is just asm instructions, skip the split stack +// prologue for speed. + +int64 runtime_cputicks(void) __attribute__((no_split_stack)); + +#endif + +// Whether the processor supports SSE2. +#if defined (__i386__) +static _Bool hasSSE2; + +// Force appropriate CPU level so that we can call the lfence/mfence +// builtins. + +#pragma GCC push_options +#pragma GCC target("sse2") + +#elif defined(__x86_64__) +#define hasSSE2 true +#endif + +#if defined(__i386__) || defined(__x86_64__) +// Whether to use lfence, as opposed to mfence. +// Set based on cpuid. +static _Bool lfenceBeforeRdtsc; +#endif // defined(__i386__) || defined(__x86_64__) + int64 runtime_cputicks(void) { -#if defined(__386__) || defined(__x86_64__) - uint32 low, high; - asm("rdtsc" : "=a" (low), "=d" (high)); - return (int64)(((uint64)high << 32) | (uint64)low); +#if defined(__i386__) || defined(__x86_64__) + if (hasSSE2) { + if (lfenceBeforeRdtsc) { + __builtin_ia32_lfence(); + } else { + __builtin_ia32_mfence(); + } + } + return __builtin_ia32_rdtsc(); #elif defined (__s390__) || defined (__s390x__) uint64 clock = 0; /* stckf may not write the return variable in case of a clock error, so make @@ -56,6 +90,10 @@ runtime_cputicks(void) #endif } +#if defined(__i386__) +#pragma GCC pop_options +#endif + void runtime_signalstack(byte *p, uintptr n) { @@ -146,8 +184,21 @@ runtime_cpuinit() #if defined(__i386__) || defined(__x86_64__) unsigned int eax, ebx, ecx, edx; + if (__get_cpuid(0, &eax, &ebx, &ecx, &edx)) { + if (eax != 0 + && ebx == 0x756E6547 // "Genu" + && edx == 0x49656E69 // "ineI" + && ecx == 0x6C65746E) { // "ntel" + lfenceBeforeRdtsc = true; + } + } if (__get_cpuid(1, &eax, &ebx, &ecx, &edx)) { setCpuidECX(ecx); +#if defined(__i386__) + if ((edx & bit_SSE2) != 0) { + hasSSE2 = true; + } +#endif } #if defined(HAVE_AS_X86_AES) |