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cmd/compile: use proved bounds to remove signed division fix-ups

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prove is able to find 94 occurrences in std cmd where a divisor
can't have the value -1. The change removes
the extraneous fix-up code for these cases.

Fixes #25239

Change-Id: Ic184de971f47cc57c702eb72805b8e291c14035d
Reviewed-on: https://go-review.googlesource.com/c/130215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
ChrisALiles 2018-08-06 19:50:38 +10:00 • committed by Brad Fitzpatrick
parent 47cc59f31f
commit 13d5cd7847
14 changed files with 299 additions and 98 deletions
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33
src/cmd/compile/internal/x86/ssa.go
View file

@ -198,24 +198,31 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
if v.Op == ssa.Op386DIVL || v.Op == ssa.Op386DIVW ||
v.Op == ssa.Op386MODL || v.Op == ssa.Op386MODW {
var c *obj.Prog
if ssa.NeedsFixUp(v) {
var c *obj.Prog
switch v.Op {
case ssa.Op386DIVL, ssa.Op386MODL:
c = s.Prog(x86.ACMPL)
j = s.Prog(x86.AJEQ)
case ssa.Op386DIVW, ssa.Op386MODW:
c = s.Prog(x86.ACMPW)
j = s.Prog(x86.AJEQ)
}
c.From.Type = obj.TYPE_REG
c.From.Reg = x
c.To.Type = obj.TYPE_CONST
c.To.Offset = -1
j.To.Type = obj.TYPE_BRANCH
}
// sign extend the dividend
switch v.Op {
case ssa.Op386DIVL, ssa.Op386MODL:
c = s.Prog(x86.ACMPL)
j = s.Prog(x86.AJEQ)
s.Prog(x86.ACDQ) //TODO: fix
s.Prog(x86.ACDQ)
case ssa.Op386DIVW, ssa.Op386MODW:
c = s.Prog(x86.ACMPW)
j = s.Prog(x86.AJEQ)
s.Prog(x86.ACWD)
}
c.From.Type = obj.TYPE_REG
c.From.Reg = x
c.To.Type = obj.TYPE_CONST
c.To.Offset = -1
j.To.Type = obj.TYPE_BRANCH
}
// for unsigned ints, we sign extend by setting DX = 0