cmd/compile: fix prove pass when upper condition is <= maxint

When the terminating condition is <= X, we need to make sure that
X+step doesn't overflow.

Fixes #53600

Change-Id: I36e5384d05b4d7168e48db6094200fcae409bfe5
Reviewed-on: https://go-review.googlesource.com/c/go/+/415219
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/ssa/loopbce.go b/src/cmd/compile/internal/ssa/loopbce.go
index 3181edca2962c002c8929444f084fb63b2f276d0..a934cd2c7b293f712ad7c23dc39264d2c8bd5e9f 100644 (file)
--- a/src/cmd/compile/internal/ssa/loopbce.go
+++ b/src/cmd/compile/internal/ssa/loopbce.go
@@ -159,6 +159,13 @@ func findIndVar(f *Func) []indVar {
                        step = -step
                }
 
+               if flags&indVarMaxInc != 0 && max.Op == OpConst64 && max.AuxInt+step < max.AuxInt {
+                       // For a <= comparison, we need to make sure that a value equal to
+                       // max can be incremented without overflowing.
+                       // (For a < comparison, the %step check below ensures no overflow.)
+                       continue
+               }
+
                // Up to now we extracted the induction variable (ind),
                // the increment delta (inc), the temporary sum (nxt),
                // the minimum value (min) and the maximum value (max).

diff --git a/test/fixedbugs/issue53600.go b/test/fixedbugs/issue53600.go
new file mode 100644 (file)
index 0000000..fd3a9e5
--- /dev/null
+++ b/test/fixedbugs/issue53600.go
@@ -0,0 +1,42 @@
+// run
+
+// Copyright 2022 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
+
+import "math"
+
+func main() {
+       f()
+       g()
+       h()
+}
+func f() {
+       for i := int64(math.MaxInt64); i <= math.MaxInt64; i++ {
+               if i < 0 {
+                       println("done")
+                       return
+               }
+               println(i, i < 0)
+       }
+}
+func g() {
+       for i := int64(math.MaxInt64) - 1; i <= math.MaxInt64; i++ {
+               if i < 0 {
+                       println("done")
+                       return
+               }
+               println(i, i < 0)
+       }
+}
+func h() {
+       for i := int64(math.MaxInt64) - 2; i <= math.MaxInt64; i += 2 {
+               if i < 0 {
+                       println("done")
+                       return
+               }
+               println(i, i < 0)
+       }
+}

diff --git a/test/fixedbugs/issue53600.out b/test/fixedbugs/issue53600.out
new file mode 100644 (file)
index 0000000..5590c7d
--- /dev/null
+++ b/test/fixedbugs/issue53600.out
@@ -0,0 +1,8 @@
+9223372036854775807 false
+done
+9223372036854775806 false
+9223372036854775807 false
+done
+9223372036854775805 false
+9223372036854775807 false
+done