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cmd/compile: in prove, infer unsigned relations while branching

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When a branch is followed, we apply the relation as described
in the domain relation table. In case the relation is in the
positive domain, we can also infer an unsigned relation if,
by that point, we know that both operands are non-negative.

Fixes #20393

Change-Id: Ieaf0c81558b36d96616abae3eb834c788dd278d5
Reviewed-on: https://go-review.googlesource.com/100278
Run-TryBot: Giovanni Bajo <rasky@develer.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Giovanni Bajo <rasky@develer.com>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Giovanni Bajo 2018-04-03 18:59:44 +02:00
parent 5c40210987
commit 29162ec9a7
2 changed files with 12 additions and 0 deletions
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3
src/cmd/compile/internal/ssa/prove.go
View File

@ -704,6 +704,9 @@ func addBranchRestrictions(ft *factsTable, b *Block, br branch) {
// When we branched from parent we learned a new set of // When we branched from parent we learned a new set of
// restrictions. Update the factsTable accordingly. // restrictions. Update the factsTable accordingly.
d := tr.d d := tr.d
if d == signed && ft.isNonNegative(c.Args[0]) && ft.isNonNegative(c.Args[1]) {
d |= unsigned
}
switch br { switch br {
case negative: case negative:
switch b.Control.Op { // Special cases switch b.Control.Op { // Special cases

9
test/prove.go
View File

@ -605,6 +605,15 @@ func trans2(a, b []int, i int) {
_ = b[i] // ERROR "Proved IsInBounds$" _ = b[i] // ERROR "Proved IsInBounds$"
} }
func trans3(a, b []int, i int) {
if len(a) > len(b) {
return
}
_ = a[i]
_ = b[i] // ERROR "Proved IsInBounds$"
}
//go:noinline //go:noinline
func useInt(a int) { func useInt(a int) {
} }