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cmd/compile: handle non-negatives in prove
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>
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@ -296,6 +296,15 @@ func (ft *factsTable) update(v, w *Value, d domain, r relation) {
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}
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}
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// isNonNegative returns true if v is known to be non-negative.
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func (ft *factsTable) isNonNegative(v *Value) bool {
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if isNonNegative(v) {
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return true
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}
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l, has := ft.limits[v.ID]
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return has && (l.min >= 0 || l.umax <= math.MaxInt64)
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}
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// checkpoint saves the current state of known relations.
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// Called when descending on a branch.
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func (ft *factsTable) checkpoint() {
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@ -608,8 +617,7 @@ func simplifyBlock(ft *factsTable, b *Block) branch {
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// to the upper bound than this is proven. Most useful in cases such as:
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// if len(a) <= 1 { return }
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// do something with a[1]
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// TODO: use constant bounds to do isNonNegative.
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if (c.Op == OpIsInBounds || c.Op == OpIsSliceInBounds) && isNonNegative(c.Args[0]) {
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if (c.Op == OpIsInBounds || c.Op == OpIsSliceInBounds) && ft.isNonNegative(c.Args[0]) {
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m := ft.get(a0, a1, signed)
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if m != 0 && tr.r&m == m {
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if b.Func.pass.debug > 0 {
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@ -29,11 +29,30 @@ func f1(a []int) int {
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}
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func f1b(a []int, i int, j uint) int {
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if i >= 0 && i < len(a) { // TODO: handle this case
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return a[i]
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if i >= 0 && i < len(a) {
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return a[i] // ERROR "Proved non-negative bounds IsInBounds$"
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}
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if i >= 10 && i < len(a) {
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return a[i] // ERROR "Proved non-negative bounds IsInBounds$"
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}
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if i >= 10 && i < len(a) {
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return a[i] // ERROR "Proved non-negative bounds IsInBounds$"
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}
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if i >= 10 && i < len(a) { // todo: handle this case
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return a[i-10]
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}
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if j < uint(len(a)) {
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return a[j] // ERROR "Proved IsInBounds"
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return a[j] // ERROR "Proved IsInBounds$"
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}
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return 0
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}
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func f1c(a []int, i int64) int {
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c := uint64(math.MaxInt64 + 10) // overflows int
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d := int64(c)
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if i >= d && i < int64(len(a)) {
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// d overflows, should not be handled.
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return a[i]
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}
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return 0
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}
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