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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/99930] Failure to optimize floating point
 -abs(x) in nontrivial code at -O2/3
Date: Tue, 06 Apr 2021 12:00:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99930

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |segher at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Seems because of r93 being live:

insn_cost 8 for     9: r93:V4SF=3D[`*.LC0']
      REG_EQUAL const_vector
insn_cost 4 for    10: {r91:SF=3Dabs(r92:SF);use r93:V4SF;clobber flags:CC;}
      REG_DEAD r92:SF
      REG_UNUSED flags:CC
insn_cost 8 for    11: r95:V4SF=3D[`*.LC1']
      REG_EQUAL const_vector
insn_cost 4 for    12: {r94:SF=3D-r91:SF;use r95:V4SF;clobber flags:CC;}
      REG_DEAD r91:SF
      REG_UNUSED flags:CC
insn_cost 4 for    13: flags:CCFP=3Dcmp(r90:SF,r94:SF)
      REG_DEAD r94:SF
insn_cost 12 for    14: pc=3D{(flags:CCFP>0)?L35:pc}
      REG_DEAD flags:CCFP
      REG_BR_PROB 59055804
insn_cost 8 for    16: r97:SF=3D[r89:DI+0x4]
      REG_DEAD r89:DI
insn_cost 4 for    18: {r96:SF=3Dabs(r97:SF);use r93:V4SF;clobber flags:CC;}
      REG_DEAD r97:SF
      REG_DEAD r93:V4SF
      REG_UNUSED flags:CC
insn_cost 4 for    20: {r99:SF=3D-r96:SF;use r95:V4SF;clobber flags:CC;}
      REG_DEAD r96:SF
      REG_DEAD r95:V4SF
      REG_UNUSED flags:CC

while at -O1 we have two loads of LC0 and r93 is dead after insn 10.=