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From: "steven at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/58517] icvt (after combine) puts ccreg clobbering insn between ccset insn and ccreg use Date: Sat, 05 Oct 2013 23:23:00 -0000 [thread overview] Message-ID: <bug-58517-4-JG8hNpxx3j@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-58517-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58517 --- Comment #4 from Steven Bosscher <steven at gcc dot gnu.org> --- So if I understand correctly, this is what happens (sorry, reading LIPSy RTL is still just too unnatural to me! ;-)) before ifcvt-after-combine: r147:=(r424>r178) r190:=r423-r189 if (r147==0) goto L433 {r190:=(~r189)+r424; r147:=X} L433: after ifcvt-after-combine: r147:=(r424>r189) r190:=r423-r189 {r945:=(~r189)+r424; r147:=X} r946:=r423-r189 r190:=(r147==0) ? r946:r945 // but r147 was clobbered! r147:=(r190==0) if (r147==0) goto L501 This is noce_try_cmove_arith: /* if (test) x = a + b; else x = c - d; => y = a + b; x = c - d; if (test) x = y; */ with "(test)" being clobbered by the assignment to "y" or "x" on the code after the transformation has been applied. noce_try_cmove_arith does not expect that the arithmetic insns emitted to load vtrue or vfalse into general operands may clobber the condition. There should be tests like this: Index: ifcvt.c =================================================================== --- ifcvt.c (revision 203224) +++ ifcvt.c (working copy) @@ -1573,6 +1573,8 @@ noce_try_cmove_arith (struct noce_if_info *if_info optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn_a))); if (insn_cost == 0 || insn_cost > COSTS_N_INSNS (if_info->branch_cost)) return FALSE; + if (modified_in_p (if_info->cond, insn_a)) + return FALSE; } else insn_cost = 0; @@ -1584,6 +1586,8 @@ noce_try_cmove_arith (struct noce_if_info *if_info optimize_bb_for_speed_p (BLOCK_FOR_INSN (insn_b))); if (insn_cost == 0 || insn_cost > COSTS_N_INSNS (if_info->branch_cost)) return FALSE; + if (modified_in_p (if_info->cond, insn_b)) + return FALSE; } /* Possibly rearrange operands to make things come out more natural. */ That's option 1 of comment #3. Option 2 is only viable if the insn computing "cond" is nearby (i.e. immediately above insn_a / insn_b), otherwise it'll be necessary to solve a code motion dataflow problem. Within one basic block that still would be doable (modified_between_p), but I doubt it's worth the trouble.
next prev parent reply other threads:[~2013-10-05 23:23 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-09-23 21:50 [Bug target/58517] New: [SH] wrong code with subc and movsicc (-mpretend-cmove) after ce2 olegendo at gcc dot gnu.org 2013-10-05 20:22 ` [Bug rtl-optimization/58517] icvt (after combine) puts ccreg clobbering insn between ccset insn and cc use olegendo at gcc dot gnu.org 2013-10-05 21:16 ` [Bug rtl-optimization/58517] icvt (after combine) puts ccreg clobbering insn between ccset insn and ccreg use olegendo at gcc dot gnu.org 2013-10-05 22:17 ` olegendo at gcc dot gnu.org 2013-10-05 23:23 ` steven at gcc dot gnu.org [this message] 2015-09-11 11:12 ` [Bug rtl-optimization/58517] ifcvt " ktkachov at gcc dot gnu.org 2023-06-02 1:38 ` pinskia at gcc dot gnu.org 2023-06-02 1:43 ` pinskia at gcc dot gnu.org 2023-06-02 1:44 ` pinskia at gcc dot gnu.org 2023-06-02 7:28 ` pinskia at gcc dot gnu.org 2023-06-02 7:57 ` pinskia at gcc dot gnu.org 2023-06-03 8:58 ` olegendo at gcc dot gnu.org 2023-06-03 9:02 ` pinskia at gcc dot gnu.org 2023-06-03 21:50 ` pinskia at gcc dot gnu.org 2023-06-03 22:18 ` pinskia at gcc dot gnu.org 2023-06-03 22:23 ` olegendo at gcc dot gnu.org 2023-06-03 22:59 ` pinskia at gcc dot gnu.org 2023-06-04 0:48 ` pinskia at gcc dot gnu.org
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