On 11/20/2021 6:14 AM, Roger Sayle wrote:
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 This patch has been tested s390/z13 with a bootstrap and a regression test (thanks to Robin Dapp), and on x86_64-pc-linux-gnu with a bootstrap and regression test just to confirm that there are no unanticipated side-effects. Ok for mainline? 2021-11-20 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.
OK jeff