On Tue, Jan 4, 2011 at 5:57 AM, Martin Reinecke <mar...@mpa-garching.mpg.de> wrote: > > > On 01/04/11 14:48, H.J. Lu wrote: >> >> On Tue, Jan 4, 2011 at 4:43 AM, Martin Reinecke >> <mar...@mpa-garching.mpg.de> wrote: >>> >>> Hi, >>> >>> while benchmarking a numerical C library making heavy use of SSE2 >>> intrinsics, I have noticed a significant (around 10 percent) slowdown >>> in the code generated by the current gcc trunk, compared to the one >>> produced by the 4.5.1 release. >>> It's quite hard to reduce the code to a small test case, but I can easily >>> point out the hot code regions where most of the CPU time is spent. >>> Do you think I should open a PR for this, or is this kind of performance >>> fluctuation to be expected? >>> >> >> What compiler flags are you using? On which processors do you >> run the library? > > The CPU is a Core2 Duo E8500; the optimization flags are > "-O2 -ffast-math -fomit-frame-pointer". > This is on a 64bit OS, so SSE2 is supported without additional > flags. > > Using "-march=native" in addition to the flags above makes the timings > worse for gcc 4.5.1 and slightly better for gcc 4.6, but still the > code generated by 4.5.1 is quite a bit faster. > The trunk version was compiled from yesterday's sources. >
We need a testcase to investigate. -- H.J.
