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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/102138] New: t = a==0 and a = PHI<0, t> should be done earlier than PRE Date: Mon, 30 Aug 2021 23:52:38 +0000 [thread overview] Message-ID: <bug-102138-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102138 Bug ID: 102138 Summary: t = a==0 and a = PHI<0, t> should be done earlier than PRE Product: gcc Version: 12.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: enhancement Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: pinskia at gcc dot gnu.org Target Milestone: --- Take: int len(int f, int l) { return l < f ? 0 : l - f + 1; } int lenzero(int f, int l) { return len(f, l) == 0; } int g(); int h(); int lenzero1(int f, int l) { if ( len(f, l) == 0) return g(); return h(); } we should be able to optimize lenzero at -O1 but don't. lenzero1 is optimized at -O1 because dom is able to jump thread. The difference in IR is: # iftmp.0_9 = PHI <0(2), iftmp.0_8(3)> _2 = iftmp.0_9 == 0; vs: # iftmp.0_13 = PHI <0(2), iftmp.0_12(3)> if (iftmp.0_13 == 0) at -O2 PRE is enabled which does the optimization. This is similar to spaceship_replacement in tree-ssa-phiopt but a more general statement of the problem.
next reply other threads:[~2021-08-30 23:52 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-08-30 23:52 pinskia at gcc dot gnu.org [this message] 2021-08-30 23:57 ` [Bug tree-optimization/102138] " pinskia at gcc dot gnu.org 2021-08-31 7:34 ` rguenth at gcc dot gnu.org 2023-11-02 18:55 ` pinskia at gcc dot gnu.org 2023-11-02 19:00 ` pinskia at gcc dot gnu.org
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