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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/96930] Failure to optimize out arithmetic with bigger size when it can't matter with division transformed into right shift Date: Sun, 03 Jan 2021 22:51:26 +0000 [thread overview] Message-ID: <bug-96930-4-FfiNWHKjOl@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-96930-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96930 --- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- The optimization is there, but just has different conditions: /* Although it would be tempting to shorten always here, that loses on some targets, since the modulo instruction is undefined if the quotient can't be represented in the computation mode. We shorten only if unsigned or if dividing by something we know != -1. */ shorten = (TYPE_UNSIGNED (TREE_TYPE (orig_op0)) || (TREE_CODE (op1) == INTEGER_CST && !integer_all_onesp (op1))); in C, and /* When dividing two signed integers, we have to promote to int. unless we divide by a constant != -1. Note that default conversion will have been performed on the operands at this point, so we have to dig out the original type to find out if it was unsigned. */ tree stripped_op1 = tree_strip_any_location_wrapper (op1); shorten = ((TREE_CODE (op0) == NOP_EXPR && TYPE_UNSIGNED (TREE_TYPE (TREE_OPERAND (op0, 0)))) || (TREE_CODE (stripped_op1) == INTEGER_CST && ! integer_all_onesp (stripped_op1))); So, in C++ we only try to shorten divisions (and modulo) if the first operand has been extended, rather than the second one. Anyway, if we optimize this in the middle-end, it won't be needed to change the FE.
next prev parent reply other threads:[~2021-01-03 22:51 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-09-03 20:47 [Bug tree-optimization/96930] New: Failure to optimize out 64-bit arithmetic when it can't happen " gabravier at gmail dot com 2020-09-04 6:41 ` [Bug tree-optimization/96930] Failure to optimize out arithmetic with bigger size when it can't matter " rguenth at gcc dot gnu.org 2021-01-02 10:04 ` jakub at gcc dot gnu.org 2021-01-02 10:53 ` jakub at gcc dot gnu.org 2021-01-03 10:24 ` gabravier at gmail dot com 2021-01-03 10:52 ` jakub at gcc dot gnu.org 2021-01-03 12:06 ` gabravier at gmail dot com 2021-01-03 14:17 ` jakub at gcc dot gnu.org 2021-01-03 22:51 ` jakub at gcc dot gnu.org [this message] 2021-01-04 13:31 ` jakub at gcc dot gnu.org 2021-01-05 15:34 ` cvs-commit at gcc dot gnu.org 2023-02-18 2:09 ` gabravier at gmail dot com
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