[Bug target/102117] s390: Inefficient code for 64x64=128 signed multiply for <= z13
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102117 Roger Sayle changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED Target Milestone|--- |12.0 --- Comment #4 from Roger Sayle --- This should now be fixed on mainline.
[Bug target/102117] s390: Inefficient code for 64x64=128 signed multiply for <= z13
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102117 --- Comment #3 from CVS Commits --- The master branch has been updated by Roger Sayle : https://gcc.gnu.org/g:dc915b361bbc99da83fc53db7f7e0e28d0ce12c8 commit r12-5436-gdc915b361bbc99da83fc53db7f7e0e28d0ce12c8 Author: Roger Sayle Date: Sun Nov 21 11:40:08 2021 + Tweak tree-ssa-math-opts.c to solve PR target/102117. This patch resolves PR target/102117 on s390. The problem is that some of the functionality of GCC's RTL expanders is no longer triggered following the transition to tree SSA form. On s390, unsigned widening multiplications are converted into WIDEN_MULT_EXPR (aka w* in tree dumps), but signed widening multiplies are left in their original form, which alas doesn't benefit from the clever logic in expand_widening_mult. The fix is to teach convert_mult_to_widen, that RTL expansion can synthesize a signed widening multiplication if the target provides a suitable umul_widen_optab. On s390-linux-gnu with -O2 -m64, the code in the bugzilla PR currently generates: imul128: stmg%r12,%r13,96(%r15) srag%r0,%r4,63 srag%r1,%r3,63 lgr %r13,%r3 mlgr%r12,%r4 msgr%r1,%r4 msgr%r0,%r3 lgr %r4,%r12 agr %r1,%r0 lgr %r5,%r13 agr %r4,%r1 stmg%r4,%r5,0(%r2) lmg %r12,%r13,96(%r15) br %r14 but with this patch should now generate the more efficient: imul128: lgr %r1,%r3 mlgr%r0,%r4 srag%r5,%r3,63 ngr %r5,%r4 srag%r4,%r4,63 sgr %r0,%r5 ngr %r4,%r3 sgr %r0,%r4 stmg%r0,%r1,0(%r2) br %r14 2021-11-21 Roger Sayle Robin Dapp gcc/ChangeLog PR target/102117 * tree-ssa-math-opts.c (convert_mult_to_widen): Recognize signed WIDEN_MULT_EXPR if the target supports umul_widen_optab. gcc/testsuite/ChangeLog PR target/102117 * gcc.target/s390/mul-wide.c: New test case. * gcc.target/s390/umul-wide.c: New test case.
[Bug target/102117] s390: Inefficient code for 64x64=128 signed multiply for <= z13
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102117 Roger Sayle changed: What|Removed |Added Ever confirmed|0 |1 Assignee|unassigned at gcc dot gnu.org |roger at nextmovesoftware dot com CC||roger at nextmovesoftware dot com Last reconfirmed||2021-11-20 Status|UNCONFIRMED |ASSIGNED --- Comment #2 from Roger Sayle --- Patch proposed: https://gcc.gnu.org/pipermail/gcc-patches/2021-November/585067.html
[Bug target/102117] s390: Inefficient code for 64x64=128 signed multiply for <= z13
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102117
--- Comment #1 from Jens Seifert ---
Sorry small bug in optimal sequence.
__int128 imul128_opt(long long a, long long b)
{
unsigned __int128 x = (unsigned __int128)(unsigned long long)a;
unsigned __int128 y = (unsigned __int128)(unsigned long long)b;
unsigned long long t1 = (a >> 63) & b;
unsigned long long t2 = (b >> 63) & a;
unsigned __int128 u128 = x * y;
unsigned long long hi = (u128 >> 64) - (t1 + t2);
unsigned long long lo = (unsigned long long)u128;
unsigned __int128 res = hi;
res <<= 64;
res |= lo;
return (__int128)res;
}
_Z11imul128_optxx:
.LFB1:
.cfi_startproc
ldgr%f2,%r12
.cfi_register 12, 17
ldgr%f0,%r13
.cfi_register 13, 16
lgr %r13,%r3
mlgr%r12,%r4
srag%r1,%r3,63
ngr %r1,%r4
srag%r4,%r4,63
ngr %r4,%r3
agr %r4,%r1
sgrk%r4,%r12,%r4
stg %r13,8(%r2)
lgdr%r12,%f2
.cfi_restore 12
lgdr%r13,%f0
.cfi_restore 13
stg %r4,0(%r2)
br %r14
.cfi_endproc
