On Fri, Jun 14, 2024 at 8:58 AM Liu, Hongtao <hongtao....@intel.com> wrote: > > > > > -----Original Message----- > > From: Richard Biener <richard.guent...@gmail.com> > > Sent: Friday, June 14, 2024 2:52 PM > > To: Kong, Lingling <lingling.k...@intel.com> > > Cc: gcc-patches@gcc.gnu.org; Liu, Hongtao <hongtao....@intel.com>; Uros > > Bizjak <ubiz...@gmail.com> > > Subject: Re: [PATCH 0/3] [APX CFCMOV] Support APX CFCMOV > > > > On Fri, Jun 14, 2024 at 5:12 AM Kong, Lingling <lingling.k...@intel.com> > > wrote: > > > > > > APX CFCMOV[1] feature implements conditionally faulting which means > > > that all memory faults are suppressed when the condition code > > > evaluates to false and load or store a memory operand. Now we could load > > or store a memory operand may trap or fault for conditional move. > > > > > > In middle-end, now we don't support a conditional move if we knew that a > > load from A or B could trap or fault. > > > > What's the cost of suppressing a fault? ISTR that for example fault > > suppression > > for vector masked load/store is quite expensive, so when this is for example > Yes, avx512 masked load/store, the cost is expensive when memory is invalid. > > done in a loop where there's always a fault that's suppressed you can see > > 1000-fold slowdown. I would suspect this is similar for cfcmov? So how is > > this > > reflected in the decision to if-convert? > But for APXF, we were told the cost of invalid memory is as cheap as valid > ones. > (Why else would this instructions be designed?)
Well - I wondered about this for the AVX512 case, so this isn't a good reason to expect it to be any better for APXF ;) But if you have confirmation this is to be expected (I would expect the silicon design with APX is finished at this point, even if actual hardware is still 2-3 years out), then fine - consider me positively surprised ;) Richard. > > > > > To enable CFCMOV, we add a target HOOK > > > TARGET_HAVE_CONDITIONAL_MOVE_MEM_NOTRAP > > > in if-conversion pass to allow convert to cmov. > > > > > > All the changes passed bootstrap & regtest x86-64-pc-linux-gnu. > > > We also tested spec with SDE and passed the runtime test. > > > > > > Ok for trunk? > > > > > > [1].https://www.intel.com/content/www/us/en/developer/articles/technic > > > al/advanced-performance-extensions-apx.html > > > > > > Lingling Kong (3): > > > [APX CFCMOV] Add a new target hook: > > TARGET_HAVE_CONDITIONAL_MOVE_MEM_NOTRAP > > > [APX CFCMOV] Support APX CFCMOV in if_convert pass > > > [APX CFCMOV] Support APX CFCMOV in backend > > > > > > gcc/config/i386/i386-expand.cc | 63 +++++ > > > gcc/config/i386/i386-opts.h | 4 +- > > > gcc/config/i386/i386.cc | 33 ++- > > > gcc/config/i386/i386.h | 1 + > > > gcc/config/i386/i386.md | 53 +++- > > > gcc/config/i386/i386.opt | 3 + > > > gcc/config/i386/predicates.md | 7 + > > > gcc/doc/tm.texi | 6 + > > > gcc/doc/tm.texi.in | 2 + > > > gcc/ifcvt.cc | 247 ++++++++++++++++++- > > > gcc/target.def | 11 + > > > gcc/targhooks.cc | 8 + > > > gcc/targhooks.h | 1 + > > > gcc/testsuite/gcc.target/i386/apx-cfcmov-1.c | 73 ++++++ > > > gcc/testsuite/gcc.target/i386/apx-cfcmov-2.c | 40 +++ > > > 15 files changed, 539 insertions(+), 13 deletions(-) create mode > > > 100644 gcc/testsuite/gcc.target/i386/apx-cfcmov-1.c > > > create mode 100644 gcc/testsuite/gcc.target/i386/apx-cfcmov-2.c > > > > > > -- > > > 2.31.1 > > >
