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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug ipa/100220] missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -O2) (inlining differences) Date: Tue, 11 Jan 2022 10:54:44 +0000 [thread overview] Message-ID: <bug-100220-4-9bypN4a4zF@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-100220-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100220 Jan Hubicka <hubicka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Depends on| |100314 --- Comment #3 from Jan Hubicka <hubicka at gcc dot gnu.org> --- Here the stack frame size of i is stimated to 244 bytes void i () { int p[8]; int n[27]; int k[24]; int l; int j; int _1; int _2; int _3; int c.2_4; int _5; <bb 2> [local count: 236223200]: l = 0; k = {}; h = &n; _1 = n[0]; _2 = _1 & 1; if (_2 != 0) goto <bb 8>; [50.00%] else goto <bb 5>; [50.00%] <bb 8> [local count: 118111600]: goto <bb 4>; [100.00%] <bb 3> [local count: 955630225]: _3 = c.2_4 + -1; c = _3; <bb 4> [local count: 1073741824]: c.2_4 = c; if (c.2_4 != 0) goto <bb 3>; [89.00%] else goto <bb 5>; [11.00%] <bb 5> [local count: 236223200]: h = &p; _5 = p[0]; if (_5 != 0) goto <bb 6>; [50.00%] else goto <bb 7>; [50.00%] <bb 6> [local count: 118111600]: h = &j; <bb 7> [local count: 236223200]: e = 0; j ={v} {CLOBBER}; l ={v} {CLOBBER}; k ={v} {CLOBBER}; n ={v} {CLOBBER}; p ={v} {CLOBBER}; return; } so it indeed has larger arrays. k is initialized but never used (so it is missed DSE). n is used in stupid way: h = &n; _1 = n[0]; where h is write only static var, but we do not know that during early opts (we could try our luck and schedule one extra writeonly detection before early optimization passes, but I am not sure it is worth). I would say that main issue is also missed DSE Referenced Bugs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100314 [Bug 100314] missed optimization for dead code elimination at -O3 (vs. -O1) (inlining differences due to missed dse)
next prev parent reply other threads:[~2022-01-11 10:54 UTC|newest] Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-22 19:25 [Bug ipa/100220] New: missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -O2) zhendong.su at inf dot ethz.ch 2021-09-25 9:49 ` [Bug ipa/100220] " pinskia at gcc dot gnu.org 2022-01-11 9:57 ` [Bug ipa/100220] missed optimization for dead code elimination at -O3 (vs. -O1, -Os, -O2) (inlining differences) rguenth at gcc dot gnu.org 2022-01-11 10:54 ` hubicka at gcc dot gnu.org [this message] 2023-08-18 2:30 ` pinskia at gcc dot gnu.org 2024-05-16 9:05 ` rguenth at gcc dot gnu.org
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