https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105338
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:1ceddd7497e15d262ead6f673f8f5ce79dd63714 commit r12-8233-g1ceddd7497e15d262ead6f673f8f5ce79dd63714 Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Apr 23 10:25:31 2022 +0200 i386: Improve ix86_expand_int_movcc [PR105338] The following testcase regressed on x86_64 on the trunk, due to some GIMPLE pass changes (r12-7687) we end up an *.optimized dump difference of: @@ -8,14 +8,14 @@ int foo (int i) <bb 2> [local count: 1073741824]: if (i_2(D) != 0) - goto <bb 4>; [35.00%] + goto <bb 3>; [35.00%] else - goto <bb 3>; [65.00%] + goto <bb 4>; [65.00%] - <bb 3> [local count: 697932184]: + <bb 3> [local count: 375809640]: <bb 4> [local count: 1073741824]: - # iftmp.0_1 = PHI <5(2), i_2(D)(3)> + # iftmp.0_1 = PHI <5(3), i_2(D)(2)> return iftmp.0_1; } and similarly for the other functions. That is functionally equivalent and there is no canonical form for those. The reason for i_2(D) in the PHI argument as opposed to 0 is the uncprop pass, that is in many cases beneficial for expansion as we don't need to load the value into some pseudo in one of the if blocks. Now, for the 11.x ordering we have the pseudo = i insn in the extended basic block (it comes first) and so forwprop1 undoes what uncprop does by propagating constant 0 there. But for the 12.x ordering, the extended basic block contains pseudo = 5 and pseudo = i is in the other bb and so fwprop1 doesn't change it. During the ce1 pass, we attempt to emit a conditional move and we have very nice code for the cases where both last operands of ?: are constant, and yet another for !TARGET_CMOVE if at least one of them is. The following patch will undo the uncprop behavior during ix86_expand_int_movcc, but just for those spots that can benefit from both or at least one operands being constant, leaving the pure cmov case as is (because then it is useful not to have to load a constant into a pseudo as it already is in one). We can do that in the op0 == op1 ? op0 : op3 or op0 != op1 ? op2 : op0 cases if op1 is a CONST_INT by pretending it is op0 == op1 ? op1 : op3 or op0 != op1 ? op2 : op1 2022-04-23 Jakub Jelinek <ja...@redhat.com> PR target/105338 * config/i386/i386-expand.cc (ix86_expand_int_movcc): Handle op0 == cst1 ? op0 : op3 like op0 == cst1 ? cst1 : op3 for the non-cmov cases. * gcc.target/i386/pr105338.c: New test.
