Hi there, I am running some numerical benchmarking on Ubuntu 11.10 with gcc 4.6.1 on an Athlon XP (Barton). I noticed that -O3 -march=athlon-xp -mfpmath=sse|both produces results twice as fast for double-precision FP-ops as -O3 -march=athlon-xp -mfpmath=387. I looked at the assembly code and found the reason to be inefficient code in the latter case. For a CPU that does not support SSE2 and above this result is slightly disconcerting as this makes selecting the correct options for producing fast code hard. I documented this here: http://mandelperformance.blogspot.com/2012/01/magic-gcc-options.html http://mandelperformance.blogspot.com/2012/01/magic-gcc-options.html It would be nice if someone commented the fact that the SSE option produces perfect 387 code while the 387 option does not :-) best regards -tomsen -- View this message in context: http://old.nabble.com/gcc-4.6.1-fpmath-options-produce-unexpected-results-tp33245187p33245187.html Sent from the gcc - Help mailing list archive at Nabble.com.
