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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/108360] [13 Regression] Dead Code Elimination Regression at -Os since r13-2048-g418b71c0d535bf Date: Tue, 10 Jan 2023 17:32:50 +0000 [thread overview] Message-ID: <bug-108360-4-yjy1lX2GH5@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-108360-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108360 --- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Seems it happens even with short b; static short c; unsigned char e; char f; void foo(); short(a)(short h, short i) { return h + i; } static short(d)(short h, int i) { return (h >= 32 || h > (7 >> i)) ? h : h << i; } unsigned g(short h, short i) { return h + i; } int main() { short j, k = -1; c = a(0 >= b, k); f = c <= 0xD315BEF1; e = f << 4; j = d(e, 5); if (3 >= g(j == b, k)) foo(); b = 32; } where we can't assume anything about b's value initially. Still in GCC 12 we decide to thread jump it based on whether e (h in inlined d) is 0 or non-0 - h >= 32 is based on ranges clearly always false and as e has [0, 16] range, h > 0 and h != 0 are the same thing, if h != 0, then d returns h, otherwise h << 5. Later on we correctly figure out that if h == 0, then h << 5 is 0. But what I really don't understand how threadfull1 in that case decided that foo will not be called.
next prev parent reply other threads:[~2023-01-10 17:32 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-01-10 13:10 [Bug tree-optimization/108360] New: Dead Code Elimination Regression at -Os (trunk vs. 12.2.0) yann at ywg dot ch 2023-01-10 14:48 ` [Bug tree-optimization/108360] [13 Regression] Dead Code Elimination Regression at -Os since r13-2048-g418b71c0d535bf marxin at gcc dot gnu.org 2023-01-10 17:00 ` jakub at gcc dot gnu.org 2023-01-10 17:32 ` jakub at gcc dot gnu.org [this message] 2023-01-10 17:45 ` jakub at gcc dot gnu.org 2023-01-10 19:18 ` amacleod at redhat dot com 2023-01-10 19:26 ` amacleod at redhat dot com 2023-01-10 19:28 ` amacleod at redhat dot com 2023-03-27 11:37 ` rguenth at gcc dot gnu.org 2023-04-08 14:37 ` law at gcc dot gnu.org 2023-04-26 6:57 ` [Bug tree-optimization/108360] [13/14 " rguenth at gcc dot gnu.org 2023-07-27 9:25 ` rguenth at gcc dot gnu.org 2023-08-07 8:53 ` pinskia at gcc dot gnu.org 2023-08-09 1:25 ` pinskia at gcc dot gnu.org 2024-05-21 9:13 ` [Bug tree-optimization/108360] [13/14/15 " jakub at gcc dot gnu.org
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