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cmd/compile: handle non-negatives in prove

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Handle this case:
if 0 <= i && i < len(a) {
        use a[i]
}

Shaves about 5k from pkg/tools/linux_amd64/*.

Change-Id: I6675ff49aa306b0d241b074c5738e448204cd981
Reviewed-on: https://go-review.googlesource.com/21431
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Alexandru Moșoi 2016-04-02 10:29:11 +02:00 • committed by Alexandru Moșoi
parent 72c1180852
commit 27ebc84716
2 changed files with 32 additions and 5 deletions
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12
src/cmd/compile/internal/ssa/prove.go
View file

@ -296,6 +296,15 @@ func (ft *factsTable) update(v, w *Value, d domain, r relation) {
}
}
// isNonNegative returns true if v is known to be non-negative.
func (ft *factsTable) isNonNegative(v *Value) bool {
if isNonNegative(v) {
return true
}
l, has := ft.limits[v.ID]
return has && (l.min >= 0 || l.umax <= math.MaxInt64)
}
// checkpoint saves the current state of known relations.
// Called when descending on a branch.
func (ft *factsTable) checkpoint() {
@ -608,8 +617,7 @@ func simplifyBlock(ft *factsTable, b *Block) branch {
// to the upper bound than this is proven. Most useful in cases such as:
// if len(a) <= 1 { return }
// do something with a[1]
// TODO: use constant bounds to do isNonNegative.
if (c.Op == OpIsInBounds || c.Op == OpIsSliceInBounds) && isNonNegative(c.Args[0]) {
if (c.Op == OpIsInBounds || c.Op == OpIsSliceInBounds) && ft.isNonNegative(c.Args[0]) {
m := ft.get(a0, a1, signed)
if m != 0 && tr.r&m == m {
if b.Func.pass.debug > 0 {