From: Keith Randall <khr@golang.org>
Date: Fri, 9 Aug 2024 17:59:43 +0000 (-0700)
Subject: cmd/compile: fix off-by-one error in prove pass
X-Git-Tag: go1.24rc1~1230
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=f259e4c916bcde5221dca99ce7d77095a21b9801;p=gostls13.git

cmd/compile: fix off-by-one error in prove pass

I think I introduced #68809 when rewriting the prove pass, by
introducing an off-by-one error here:
https://go-review.googlesource.com/c/go/+/599096/5/src/cmd/compile/internal/ssa/prove.go
lines 872-874.
The min++ is already handled in one of the two following cases with
the (r&eq==0) condition. Move the min++ to just the other case.

Fixes #68809

Change-Id: Iffae99e29219c94aaf584cd7ae247289fa604a00
Reviewed-on: https://go-review.googlesource.com/c/go/+/604100
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---

diff --git a/src/cmd/compile/internal/ssa/prove.go b/src/cmd/compile/internal/ssa/prove.go
index c2ac6ca40f..d563204565 100644
--- a/src/cmd/compile/internal/ssa/prove.go
+++ b/src/cmd/compile/internal/ssa/prove.go
@@ -1059,9 +1059,6 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) {
 					// We know that either x>min OR x<=max. factsTable cannot record OR conditions,
 					// so let's see if we can already prove that one of them is false, in which case
 					// the other must be true
-					if r == gt {
-						min++
-					}
 					l := ft.limits[x.ID]
 					if l.max <= min {
 						if r&eq == 0 || l.max < min {
@@ -1070,6 +1067,9 @@ func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) {
 						}
 					} else if l.min > max {
 						// x<=max is impossible, so it must be x>min
+						if r == gt {
+							min++
+						}
 						ft.signedMin(x, min)
 					}
 				}
diff --git a/test/fixedbugs/issue68809.go b/test/fixedbugs/issue68809.go
new file mode 100644
index 0000000000..67afda6708
--- /dev/null
+++ b/test/fixedbugs/issue68809.go
@@ -0,0 +1,19 @@
+// run
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func main() {
+	cnt := 0
+	for i := 1; i <= 11; i++ {
+		if i-6 > 4 {
+			cnt++
+		}
+	}
+	if cnt != 1 {
+		panic("bad")
+	}
+}