cmd/compile: don't report newLimit discovered when unsat happens multiple times

Fixes #71852

Change-Id: I696fcb8fc8c0c2e5e5ae6ab50596f6bdb9b7d498
Reviewed-on: https://go-review.googlesource.com/c/go/+/650975
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/prove.go

@@ -552,8 +552,9 @@ func (ft *factsTable) newLimit(v *Value, newLim limit) bool {
 	}
 
 	if lim.unsat() {
+		r := !ft.unsat
 		ft.unsat = true
-		return true
+		return r
 	}
 
 	// Check for recursion. This normally happens because in unsatisfiable

test/fixedbugs/issue71852.go

@@ -0,0 +1,23 @@
+// compile
+
+// Copyright 2025 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() {
+	test(2)
+}
+
+func test(i int) {
+	if i <= 0 {
+		return
+	}
+
+	_ = math.Pow10(i + 2)
+}