Ping (in hopes that someone can review before the weekend). On Sat, 2023-06-03 at 19:25 +0800, Xi Ruoyao wrote: > We used to skip ifunc check when CX16 is available. But now we use > CX16+AVX+Intel/AMD for the "perfect" 16b load implementation, so CX16 > alone is not a sufficient reason not to use ifunc (see PR104688). > > This causes a subtle and annoying issue: when GCC is built with a > higher -march= setting in CFLAGS_FOR_TARGET, ifunc is disabled and > the worst (locked) implementation of __atomic_load_16 is always used. > > There seems no good way to check if the CPU is Intel or AMD from > the built-in macros (maybe we can check every known model like > __skylake, > __bdver2, ..., but it will be very error-prune and require an update > whenever we add the support for a new x86 model). The best thing we > can > do seems "always try ifunc" here. > > Bootstrapped and tested on x86_64-linux-gnu. Ok for trunk? > > libatomic/ChangeLog: > > * configure.tgt: For x86_64, always set try_ifunc=yes. > --- > libatomic/configure.tgt | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/libatomic/configure.tgt b/libatomic/configure.tgt > index a92ae9e8309..39dd5686f2e 100644 > --- a/libatomic/configure.tgt > +++ b/libatomic/configure.tgt > @@ -100,9 +100,7 @@ EOF > fi > cat > conftestx.c <<EOF > #ifdef __x86_64__ > -#ifndef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 > -#error need -mcx16 > -#endif > +#error ifunc is always wanted for 16B atomic load > #else > #ifndef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 > #error need -march=i686
-- Xi Ruoyao <xry...@xry111.site> School of Aerospace Science and Technology, Xidian University
