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cmd/compile/internal/x86: simplify 387 with FLDZ and FLZ1

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FLD1 pushes +1.0 to the 387 register stack, and FLDZ pushes +0.0
to the 387 regiser stack.

They can be used to simplify MOVSSconst/MOVSDconst when the
constant is +0.0, -0.0, +1.0, -1.0.

The size of the go executable reduces about 62KB and the total size
of pkg/linux_386 reduces about 7KB with this optimization.

Change-Id: Icc8213b58262e0024a277cf1103812a17dd4b05e
Reviewed-on: https://go-review.googlesource.com/119635
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Ben Shi 2018-06-19 03:44:28 +00:00
parent 5403b8eceb
commit bd483592a2
1 changed files with 18 additions and 5 deletions
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23
src/cmd/compile/internal/x86/387.go
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@ -22,11 +22,24 @@ func ssaGenValue387(s *gc.SSAGenState, v *ssa.Value) {
switch v.Op {
case ssa.Op386MOVSSconst, ssa.Op386MOVSDconst:
p := s.Prog(loadPush(v.Type))
p.From.Type = obj.TYPE_FCONST
p.From.Val = math.Float64frombits(uint64(v.AuxInt))
p.To.Type = obj.TYPE_REG
p.To.Reg = x86.REG_F0
iv := uint64(v.AuxInt)
if iv == 0x0000000000000000 { // +0.0
s.Prog(x86.AFLDZ)
} else if iv == 0x3ff0000000000000 { // +1.0
s.Prog(x86.AFLD1)
} else if iv == 0x8000000000000000 { // -0.0
s.Prog(x86.AFLDZ)
s.Prog(x86.AFCHS)
} else if iv == 0xbff0000000000000 { // -1.0
s.Prog(x86.AFLD1)
s.Prog(x86.AFCHS)
} else { // others
p := s.Prog(loadPush(v.Type))
p.From.Type = obj.TYPE_FCONST
p.From.Val = math.Float64frombits(iv)
p.To.Type = obj.TYPE_REG
p.To.Reg = x86.REG_F0
}
popAndSave(s, v)
case ssa.Op386MOVSSconst2, ssa.Op386MOVSDconst2: