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cmd/compile: should use FNEG for float32/64 on ppc64 #9598

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minux opened this issue Jan 15, 2015 · 4 comments
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cmd/compile: should use FNEG for float32/64 on ppc64 #9598

minux opened this issue Jan 15, 2015 · 4 comments
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@minux
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minux commented Jan 15, 2015

It always generates FMUL -1 for OMINUS now.
However, Power does support double precision FNEG, it just
doesn't support single precision FNEGS.

But it's still fine to use FNEG for both float32 and float64, as
Power ISA documents that FNEG simply inverts bit 0.
@minux minux self-assigned this Jan 15, 2015
@minux minux added this to the Go1.5 milestone Jan 15, 2015
@minux minux changed the title cmd/9g: should use AFNEG for float64 cmd/9g: should use FNEG for float64 Jan 15, 2015
@minux minux changed the title cmd/9g: should use FNEG for float64 cmd/9g: should use FNEG for float32/64 Jan 15, 2015
@rsc
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rsc commented Jun 8, 2015

I believe this is too unimportant for right now. Finishing the port (especially those nagging cgo details) takes priority over microoptimizations. Removing milestone.

@rsc rsc modified the milestones: Unplanned, Go1.5 Jun 8, 2015
@rsc rsc changed the title cmd/9g: should use FNEG for float32/64 cmd/compile: should use FNEG for float32/64 on ppc64 Jun 8, 2015
@josharian
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@dr2chase does ppc64 SSA do this? Can we close this issue?

@dr2chase
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It should be fixed in 1.8:

(Neg64F x) -> (FNEG x)
(Neg32F x) -> (FNEG x)

    {name: "FNEG", argLength: 1, reg: fp11, asm: "FNEG"},   // -arg0 (floating point)

    case ssa.OpPPC64NEG, ssa.OpPPC64FNEG, ssa.OpPPC64FSQRT, ssa.OpPPC64FSQRTS, ssa.OpPPC64FCTIDZ, ssa.OpPPC64FCTIWZ, ssa.OpPPC64FCFID, ssa.OpPPC64FRSP:
        r := gc.SSARegNum(v)
        p := gc.Prog(v.Op.Asm())

@josharian
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Thanks. Closing.

@golang golang locked and limited conversation to collaborators Aug 19, 2017
@rsc rsc unassigned minux Jun 23, 2022
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@josharian @rsc @minux @dr2chase @gopherbot