2011/3/22 Ian Lance Taylor <iant@xxxxxxxxxx>: > Zuxy Meng <zuxy.meng@xxxxxxxxx> writes: > >> 2011/3/22 Ian Lance Taylor <iant@xxxxxxxxxx>: >>> "Zuxy Meng" <zuxy.meng@xxxxxxxxx> writes: >>> >>>> I found that gcc 4.5 generates "rep ret" even under -march=core2. Does >>>> an Intel CPU benefit from this optimization too? >>> >>> As far as I know no Intel CPU benefits. Note that -march selects the >>> architecture but not the tuning. The default tuning uses "rep; ret" >>> when appropriate. If you want to avoid it, use a -mtune option. >> >> 'info gcc' tells me that '-march=CPU-TYPE' implies '-mtune=CPU-TYPE', >> at least for x86... > > You're quite right, sorry about that. > > gcc 4.5 will use "rep; ret" for K8, Athlon, AMDFam10, Core2, and > generic. Looking into the change history, I see that gcc has padded > returns for Core2 ever since Core2 support was added here: > http://gcc.gnu.org/ml/gcc-patches/2006-11/msg00860.html . I suspect > that Vlad just copied the generic tunings for Core2, and didn't notice > that there was no particular reason to pad returns for Core2. > > Please consider opening a bug report per http://gcc.gnu.org/bugs/ with > this information. Thanks. Filed as http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48227 -- Zuxy Beauty is truth, While truth is beauty. PGP KeyID: E8555ED6
