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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/71775] Redundant move instruction for sign extension Date: Sat, 07 Aug 2021 04:53:55 +0000 [thread overview] Message-ID: <bug-71775-4-Qyz5Y6KraP@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-71775-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71775 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Ever confirmed|0 |1 Status|UNCONFIRMED |NEW Severity|normal |enhancement Component|target |rtl-optimization Keywords| |missed-optimization Last reconfirmed| |2021-08-07 --- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Confirmed: Trying 11 -> 13: 11: {r87:DI=ctz(r86:DI);clobber flags:CC;} REG_UNUSED flags:CC 13: r88:DI=sign_extend(r87:DI#0) REG_DEAD r87:DI Failed to match this instruction: (set (reg:DI 88 [ _1 ]) (sign_extend:DI (subreg:SI (ctz:DI (reg/v:DI 86 [ x ])) 0))) Part of the problem is ctz has an unkown value at 0 but we know x is non-zero (well kinda, at the gimple level we do). We do the right thing on aarch64 because we know the value at 0. Trying 11 -> 13: 11: r97:DI=ctz(r96:DI) 13: r98:DI=sign_extend(r97:DI#0) REG_DEAD r97:DI Successfully matched this instruction: (set (reg:DI 98 [ _1 ]) (ctz:DI (reg/v:DI 96 [ x ]))) allowing combination of insns 11 and 13 original costs 8 + 4 = 12 replacement cost 8 deferring deletion of insn with uid = 11. modifying insn i3 13: r98:DI=ctz(r96:DI) deferring rescan insn with uid = 13. So this requires us to bring the range down from gimple to RTL. Here is the range: # RANGE [1, 18446744073709551615] # x_12 = PHI <x_10(3), x_6(D)(2)>
next parent reply other threads:[~2021-08-07 4:53 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <bug-71775-4@http.gcc.gnu.org/bugzilla/> 2021-08-07 4:53 ` pinskia at gcc dot gnu.org [this message] 2022-08-03 7:58 ` cvs-commit at gcc dot gnu.org
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