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cmd/compile: derive relation between x+delta and x in prove

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If x+delta cannot overflow/underflow, we can derive:
  x+delta < x if delta<0 (this CL included)
  x+delta > x if delta>0 (this CL not included due to
  a recursive stack overflow)

Remove 95 bounds checks during ./make.bat

Fixes #51622

Change-Id: I60d9bd84c5d7e81bbf808508afd09be596644f09
Reviewed-on: https://go-review.googlesource.com/c/go/+/406175
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
This commit is contained in:
Wayne Zuo 2022-05-13 23:52:48 +08:00 • committed by Daniel Martí
parent 6b113c0fec
commit d2e0587f77
2 changed files with 26 additions and 9 deletions
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20
src/cmd/compile/internal/ssa/prove.go
View file

@ -463,15 +463,23 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) {
if parent.Func.pass.debug > 1 {
parent.Func.Warnl(parent.Pos, "x+d %s w; x:%v %v delta:%v w:%v d:%v", r, x, parent.String(), delta, w.AuxInt, d)
}
underflow := true
if l, has := ft.limits[x.ID]; has && delta < 0 {
if (x.Type.Size() == 8 && l.min >= math.MinInt64-delta) ||
(x.Type.Size() == 4 && l.min >= math.MinInt32-delta) {
underflow = false
}
}
if delta < 0 && !underflow {
// If delta < 0 and x+delta cannot underflow then x > x+delta (that is, x > v)
ft.update(parent, x, v, signed, gt)
}
if !w.isGenericIntConst() {
// If we know that x+delta > w but w is not constant, we can derive:
// if delta < 0 and x > MinInt - delta, then x > w (because x+delta cannot underflow)
// if delta < 0 and x+delta cannot underflow, then x > w
// This is useful for loops with bounds "len(slice)-K" (delta = -K)
if l, has := ft.limits[x.ID]; has && delta < 0 {
if (x.Type.Size() == 8 && l.min >= math.MinInt64-delta) ||
(x.Type.Size() == 4 && l.min >= math.MinInt32-delta) {
ft.update(parent, x, w, signed, r)
}
if delta < 0 && !underflow {
ft.update(parent, x, w, signed, r)
}
} else {
// With w,delta constants, we want to derive: x+delta > w ⇒ x > w-delta