https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102117
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:dc915b361bbc99da83fc53db7f7e0e28d0ce12c8 commit r12-5436-gdc915b361bbc99da83fc53db7f7e0e28d0ce12c8 Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Sun Nov 21 11:40:08 2021 +0000 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 <ro...@nextmovesoftware.com> Robin Dapp <rd...@linux.ibm.com> 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.
