On 23/03/2014 23:34, Laurent GUERBY wrote: > On Sun, 2014-03-23 at 20:50 +0100, Loic Dachary wrote: >> Hi Laurent, >> >> In the context of optimizing erasure code functions implemented by >> Kevin Greenan (cc'ed) and James Plank at >> https://bitbucket.org/jimplank/gf-complete/ we ran accross a question >> you may have the answer to: can gcc -msse2 (or -msse* for that matter >> ) have a negative impact on the portability of the compiled binary >> code ? >> >> In other words, if a code is compiled without -msse* and runs fine on >> all intel processors it targets, could it be that adding -msse* to the >> compilation of the same source code generate a binary that would fail >> on some processors ? This is assuming no sse specific functions were >> used in the source code. >> >> In gf-complete, all sse specific instructions are carefully protected >> to not be run on a CPU that does not support them. The runtime >> detection is done by checking CPU id bits ( see >> https://bitbucket.org/jimplank/gf-complete/pull-request/7/probe-intel-sse-features-at-runtime/diff#Lsrc/gf_intel.cT28 ) >> >> The corresponding thread is at: >> >> https://bitbucket.org/jimplank/gf-complete/pull-request/4/defer-the-decision-to-use-a-given-sse/diff#comment-1479296 >> >> Cheers >> > > Hi Loic, > > The GCC documentation is here with lists of architecture supporting > sse/sse2: > > http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/i386-and-x86-64-Options.html#i386-and-x86-64-Options > > So unless you want to run your code a very very old x86 32 bit processor > "-msse" shouldn't be an issue. "-msse2" is similar. This is good to know :) Should I be worried about unintended side effects of -msse4.2 -mssse3 -msse4.1 or -mpclmul ? These are the flags that gf-complete are using, specifically. Cheers > > -mtune=xxx with xxx being a recent arch could be interesting for you > because it keeps compatibility with the generic arch while tuning > resulting code on the specific arch (for example the current fashionable > arch like corei7). > > For alibrary you can choose the code you execute a load/run time > for a specific function by using the STT_GNU_IFUNC feature : > > http://vger.kernel.org/~davem/cgi-bin/blog.cgi/2010/02/07 > http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Function-Attributes.html#index-g_t_0040code_007bifunc_007d-attribute-2529 > > I believe recent GLIBC use this feature to tune > some performance/arch sensitive functions. > > Sincerely, > > Laurent > > -- Loïc Dachary, Artisan Logiciel Libre
Attachment:
signature.asc
Description: OpenPGP digital signature
