[release-branch.go1.21] cmd/compile: fix escape analysis of string mi…

…n/max

When I was plumbing min/max support through the compiler, I was
thinking mostly about numeric argument types. As a result, I forgot
that escape analysis would need to be aware that min/max can operate
on string values, which contain pointers.

Updates #64565.
Fixes #64567.

Change-Id: I36127ce5a2da942401910fa0f9de922726c9f94d
Reviewed-on: https://go-review.googlesource.com/c/go/+/547715
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Mauri de Souza Meneguzzo <[email protected]>
Auto-Submit: Matthew Dempsky <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
(cherry picked from commit 34416d7)
Reviewed-on: https://go-review.googlesource.com/c/go/+/547757
Reviewed-by: Cuong Manh Le <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

src/cmd/compile/internal/escape/call.go

@@ -186,14 +186,22 @@ func (e *escape) callCommon(ks []hole, call ir.Node, init *ir.Nodes, wrapper *ir
 		argument(e.discardHole(), &call.X)
 		argument(e.discardHole(), &call.Y)
 
-	case ir.ODELETE, ir.OMAX, ir.OMIN, ir.OPRINT, ir.OPRINTN, ir.ORECOVER:
+	case ir.ODELETE, ir.OPRINT, ir.OPRINTN, ir.ORECOVER:
 		call := call.(*ir.CallExpr)
 		fixRecoverCall(call)
 		for i := range call.Args {
 			argument(e.discardHole(), &call.Args[i])
 		}
 		argumentRType(&call.RType)
 
+	case ir.OMIN, ir.OMAX:
+		call := call.(*ir.CallExpr)
+		fixRecoverCall(call)
+		for i := range call.Args {
+			argument(ks[0], &call.Args[i])
+		}
+		argumentRType(&call.RType)
+
 	case ir.OLEN, ir.OCAP, ir.OREAL, ir.OIMAG, ir.OCLOSE, ir.OCLEAR:
 		call := call.(*ir.UnaryExpr)
 		argument(e.discardHole(), &call.X)

test/escape_calls.go

@@ -52,3 +52,10 @@ func bar() {
 	s := "string"
 	f([]string{s}) // ERROR "\[\]string{...} escapes to heap"
 }
+
+func strmin(a, b, c string) string { // ERROR "leaking param: a to result ~r0 level=0" "leaking param: b to result ~r0 level=0" "leaking param: c to result ~r0 level=0"
+	return min(a, b, c)
+}
+func strmax(a, b, c string) string { // ERROR "leaking param: a to result ~r0 level=0" "leaking param: b to result ~r0 level=0" "leaking param: c to result ~r0 level=0"
+	return max(a, b, c)
+}

test/fixedbugs/issue64565.go

@@ -0,0 +1,15 @@
+// run
+
+// Copyright 2023 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() {
+	m := "0"
+	for _, c := range "321" {
+		m = max(string(c), m)
+		println(m)
+	}
+}

test/fixedbugs/issue64565.out

@@ -0,0 +1,3 @@
+3
+3
+3