Re: [Patch, i386] Support BMI and BMI2 targets in multiversioning

[Allan Sandfeld Jensen <carewolf at gmail dot com>]

On Monday 26 January 2015, you wrote:
> On Mon, Jan 26, 2015 at 10:38 AM, Allan Sandfeld Jensen
> 
> <allan@carewolf.com> wrote:
> > On Monday 26 January 2015, H.J. Lu wrote:
> >> On Sun, Jan 25, 2015 at 10:37 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> >> > On Sun, Jan 25, 2015 at 7:23 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> >> >> On Sat, Jan 24, 2015 at 11:49 AM, Allan Sandfeld Jensen
> >> >> 
> >> >> <allan@carewolf.com> wrote:
> >> >>> On Saturday 24 January 2015, Uros Bizjak wrote:
> >> >>>> On Mon, Jan 12, 2015 at 6:02 PM, Uros Bizjak <ubizjak@gmail.com> 
wrote:
> >> >>>> > Hello!
> >> >>>> > 
> >> >>>> >>> On Wed, Dec 31, 2014 at 01:28:47PM +0100, Allan Sandfeld Jensen
> > 
> > wrote:
> >> >>>> >>> > I recently wanted to use multiversioning for BMI2 specific
> >> >>>> >>> > extensions PDEP/PEXT, and noticed it wasn't there. So I wrote
> >> >>>> >>> > this patch to add it, and also added AES, F16C and BMI1 for
> >> >>>> >>> > completeness.
> >> >>>> >>> 
> >> >>>> >>> AES nor F16C doesn't make any sense IMHO for multiversioning,
> >> >>>> >>> you need special intrinsics for that anyway and when you use
> >> >>>> >>> them, the function will fail to compile without those
> >> >>>> >>> features. Multiversioning only makes sense for ISA features
> >> >>>> >>> the compiler uses for normal C/C++ code without any
> >> >>>> >>> intrinsics.
> >> >>>> >> 
> >> >>>> >> Patch reduced to just adding BMI and BMI2 multiversioning:
> >> >>>> > +2014-12-29  Allan Sandfeld Jensen  <sandfeld@kde.org>
> >> >>>> > +
> >> >>>> > + * config/i386/i386.c (get_builtin_code_for_version): Add
> >> >>>> > + support for BMI and BMI2 multiversion functions.
> >> >>>> > 
> >> >>>> > +2014-12-29  Allan Sandfeld Jensen  <sandfeld@kde.org>
> >> >>>> > +
> >> >>>> > + * gcc.target/i386/funcspec-5.c: Test new multiversion targets.
> >> >>>> > + * g++.dg/ext/mv17.C: Test BMI/BMI2 multiversion dispatcher.
> >> >>>> > 
> >> >>>> > +2014-12-29  Allan Sandfeld Jensen  <sandfeld@kde.org>
> >> >>>> > +
> >> >>>> > + * config/i386/cpuinfo.c (enum processor_features): Add
> >> >>>> > FEATURE_BMI and + FEATURE_BMI2.
> >> >>>> > + (get_available_features): Detect FEATURE_BMI and FEATURE_BMI2.
> >> >>>> > 
> >> >>>> > OK for mainline
> >> >>>> 
> >> >>>> Allan, did you commit the patch to mainline? I don't see it in SVN
> >> >>>> logs.
> >> >>>> 
> >> >>>> (If you don't have SVN commit access, please mention it in the
> >> >>>> patch submission, so someone will commit the patch for you).
> >> >>> 
> >> >>> Sorry. I don't have SVN commit access.
> >> >> 
> >> >> Committed with a bunch of fixes (e.g. missing fold_builtin_cpu part
> >> >> in gcc/config/i386/i386.c, and mv17.C test didn't compile at all due
> >> >> to missing parenthesis).
> >> > 
> >> > ... and now with committed ChangeLog and patch.
> >> > 
> >> > gcc/ChangeLog:
> >> >     * config/i386/i386.c (get_builtin_code_for_version): Add
> >> >     support for BMI and BMI2 multiversion functions.
> >> >     (fold_builtin_cpu): Add F_BMI and F_BMI2.
> >> > 
> >> > libgcc/ChangeLog:
> >> >     * config/i386/cpuinfo.c (enum processor_features): Add FEATURE_BMI
> >> >     and FEATURE_BMI2.
> >> >     (get_available_features): Detect FEATURE_BMI and FEATURE_BMI2.
> >> > 
> >> > testsuite/ChangeLog:
> >> >     * gcc.target/i386/funcspec-5.c: Test new multiversion targets.
> >> >     * g++.dg/ext/mv17.C: Test BMI/BMI2 multiversion dispatcher.
> >> 
> >> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> >> index 9ec40cb..441911d 100644
> >> --- a/gcc/config/i386/i386.c
> >> +++ b/gcc/config/i386/i386.c
> >> @@ -34289,15 +34289,18 @@ get_builtin_code_for_version (tree decl, tree
> >> *predica te_list)
> >> 
> >>      P_PROC_SSE4_A,
> >>      P_SSE4_1,
> >>      P_SSE4_2,
> >> 
> >> -    P_PROC_SSE4_2,
> >> 
> >>      P_POPCNT,
> >> 
> >> +    P_PROC_SSE4_2,
> >> 
> >>      P_AVX,
> >>      P_PROC_AVX,
> >> 
> >> +    P_BMI,
> >> +    P_PROC_BMI,
> >> 
> >>      P_FMA4,
> >>      P_XOP,
> >>      P_PROC_XOP,
> >>      P_FMA,
> >>      P_PROC_FMA,
> >> 
> >> +    P_BMI2,
> >> 
> >>      P_AVX2,
> >>      P_PROC_AVX2,
> >>      P_AVX512F,
> >> 
> >> This changed the priority of P_POPCNT and caused
> >> 
> >> FAIL: g++.dg/ext/mv1.C  -std=gnu++98 execution test
> >> FAIL: g++.dg/ext/mv1.C  -std=gnu++11 execution test
> >> FAIL: g++.dg/ext/mv1.C  -std=gnu++14 execution test
> >> 
> >> on Nehalem and Westmere machines:
> >> 
> >> mv1.exe:
> >> /export/gnu/import/git/sources/gcc/gcc/testsuite/g++.dg/ext/mv1.C:51:
> >> int main(): Assertion `val == 5' failed.
> >> 
> >> since "val" is 6 now.
> > 
> > Right. I am not sure why popcnt was prioritized below arch=corei7. The
> > logic is supposed to be that any target that includes an extension is
> > prioritized
> 
> I don't understand your question.  popcnt feature is separate from -march.
> Its priority has nothing to do with -march=corei7.
> 
arch=corei7 implies popcnt. See PTA_NEHALEM in i386.c. The test would probably 
work with -march=core2.

AFAIK The logic of the priorities in multiversioning is that architecture 
specific functions are chosen over feature specific, unless the feature is one 
that isn't required by the architecture.

`Allan