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From: Richard Biener <rguenth@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-3879] better PHI copy propagation for forwprop Date: Thu, 10 Nov 2022 14:19:58 +0000 (GMT) [thread overview] Message-ID: <20221110141958.9F2D7383666C@sourceware.org> (raw) https://gcc.gnu.org/g:f1b76811f2c3773e8cabcc07932bf13e82e264db commit r13-3879-gf1b76811f2c3773e8cabcc07932bf13e82e264db Author: Richard Biener <rguenther@suse.de> Date: Thu Nov 10 15:02:37 2022 +0100 better PHI copy propagation for forwprop We can handle _1 = PHI <_1, _2> as a copy. PR tree-optimization/84646 * tree-ssa-forwprop.cc (pass_forwprop::execute): Improve copy propagation across PHIs. Diff: --- gcc/tree-ssa-forwprop.cc | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc index 4b693ef095c..7c7942600ef 100644 --- a/gcc/tree-ssa-forwprop.cc +++ b/gcc/tree-ssa-forwprop.cc @@ -3384,7 +3384,12 @@ pass_forwprop::execute (function *fun) FOR_EACH_PHI_ARG (use_p, phi, it, SSA_OP_USE) { tree use = USE_FROM_PTR (use_p); - if (! first) + if (use == res) + /* The PHI result can also appear on a backedge, if so + we can ignore this case for the purpose of determining + the singular value. */ + ; + else if (! first) first = use; else if (! operand_equal_p (first, use, 0)) {
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