[release-branch.go1.20] cmd/compile: don't set range expr key/value type if already set

Unified IR already records the correct type for them.

Fixes #59450

Change-Id: I275c45b48f67bde55c8e2079d60b5868d0acde7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/481555
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/482655
Auto-Submit: Michael Knyszek <mknyszek@google.com>

2 files changed, 27 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/typecheck/stmt.go b/src/cmd/compile/internal/typecheck/stmt.go
index 9d57edb39f..fca06deaa1 100644
--- a/src/cmd/compile/internal/typecheck/stmt.go
+++ b/src/cmd/compile/internal/typecheck/stmt.go
@@ -71,7 +71,7 @@ func typecheckrangeExpr(n *ir.RangeStmt) {
 
 	do := func(nn ir.Node, t *types.Type) {
 		if nn != nil {
-			if ir.DeclaredBy(nn, n) {
+			if ir.DeclaredBy(nn, n) && nn.Type() == nil {
 				nn.SetType(t)
 			} else if nn.Type() != nil {
 				if op, why := Assignop(t, nn.Type()); op == ir.OXXX {
diff --git a/test/fixedbugs/issue59378.go b/test/fixedbugs/issue59378.go
new file mode 100644
index 0000000000..8ff198eaa7
--- /dev/null
+++ b/test/fixedbugs/issue59378.go
@@ -0,0 +1,26 @@
+// compile
+
+// 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 p
+
+func f() {
+	F([]int{}, func(*int) bool { return true })
+}
+
+func F[S []E, E any](a S, fn func(*E) bool) {
+	for _, v := range a {
+		G(a, func(e E) bool { return fn(&v) })
+	}
+}
+
+func G[E any](s []E, f func(E) bool) int {
+	for i, v := range s {
+		if f(v) {
+			return i
+		}
+	}
+	return -1
+}