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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/103218] New: (a < 0) << signbit is not always optimized to a & signbitmask at the gimple level Date: Sat, 13 Nov 2021 01:40:38 +0000 [thread overview] Message-ID: <bug-103218-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103218 Bug ID: 103218 Summary: (a < 0) << signbit is not always optimized to a & signbitmask at the gimple level Product: gcc Version: 12.0 Status: UNCONFIRMED Keywords: missed-optimization, TREE 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 f(signed char a) { signed char t = a < 0; return (unsigned char)(t << 7); } At the gimple level we get: int f(signed char a) { signed char t = a < 0; return (unsigned char)(t << 7); } But combine is able to it: Trying 9 -> 10: 9: {r89:QI=r91:SI#0 0>>0x7;clobber flags:CC;} REG_DEAD r91:SI REG_UNUSED flags:CC 10: {r90:QI=r89:QI<<0x7;clobber flags:CC;} REG_DEAD r89:QI REG_UNUSED flags:CC Successfully matched this instruction: (parallel [ (set (reg:QI 90) (and:QI (subreg:QI (reg:SI 91) 0) (const_int -128 [0xffffffffffffff80]))) (clobber (reg:CC 17 flags)) ]) allowing combination of insns 9 and 10 original costs 4 + 4 = 8 replacement cost 4 deferring deletion of insn with uid = 9. modifying insn i3 10: {r90:QI=r91:SI#0&0xffffffffffffff80;clobber flags:CC;} REG_DEAD r91:SI REG_UNUSED flags:CC deferring rescan insn with uid = 10. If we had wrote the testcase like: int f(signed char a) { return (a < 0) << 7; } GCC does optimize it to: (int) NON_LVALUE_EXPR <a> & 128
next reply other threads:[~2021-11-13 1:40 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-11-13 1:40 pinskia at gcc dot gnu.org [this message] 2021-11-13 1:41 ` [Bug tree-optimization/103218] " pinskia at gcc dot gnu.org 2021-11-13 1:59 ` pinskia at gcc dot gnu.org 2021-11-13 2:11 ` pinskia at gcc dot gnu.org 2021-11-13 6:47 ` pinskia at gcc dot gnu.org 2021-11-13 20:15 ` pinskia at gcc dot gnu.org 2021-11-16 15:09 ` cvs-commit at gcc dot gnu.org 2021-11-16 15:10 ` pinskia at gcc dot gnu.org
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