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Remove useless -mbmi flag in Makefile

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I could not find anything documented that is necessary that prepending -mbmi to -mbmi2 gives some benefit.
Instead at
https://gcc.gnu.org/onlinedocs/gcc/x86-Built-in-Functions.html#x86-Built-in-Functions

The following built-in functions are available when -mbmi is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);

The following built-in functions are available when -mbmi2 is used. All of them generate the machine instruction that is part of the name.
unsigned int _bzhi_u32 (unsigned int, unsigned int)
unsigned int _pdep_u32 (unsigned int, unsigned int)
unsigned int _pext_u32 (unsigned int, unsigned int)
unsigned long long _bzhi_u64 (unsigned long long, unsigned long long)
unsigned long long _pdep_u64 (unsigned long long, unsigned long long)
unsigned long long _pext_u64 (unsigned long long, unsigned long long)

and at
https://gcc.gnu.org/ml/gcc/2014-02/msg00204.html

( "... The real optimization comes from being able to use pext
(parallel bit extract), which can implement several bextr expressions in
parallel.")

Apart from that we don't use all -msse -msse2 -msse3 -msse4.2 etc. but just -msse3 (or -msse4.2) only.

As regards to the speedup within noise level - this pull request is actually reversal of mcostalba#198 wherein prepending -mbmi to -mbmi2 was claimed to be 0.3% faster and here (removing -mbmi) gives 0.4% speed gain.
This commit is contained in:
Krgp 2016-04-30 16:08:14 +05:30 • committed by Marco Costalba
parent 2694ef23c3
commit 8f934dff9a
1 changed files with 1 additions and 1 deletions
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2
src/Makefile
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@ -309,7 +309,7 @@ endif
ifeq ($(pext),yes) ifeq ($(pext),yes)
CXXFLAGS += -DUSE_PEXT CXXFLAGS += -DUSE_PEXT
ifeq ($(comp),$(filter $(comp),gcc clang mingw)) ifeq ($(comp),$(filter $(comp),gcc clang mingw))
CXXFLAGS += -mbmi -mbmi2 CXXFLAGS += -mbmi2
endif endif
endif endif