cmd/compile: fix clear on slice with zero size elem

Fixed #61127

Change-Id: If07b04ebcc98438c66f273c0c94bea1f230dc2e8
Reviewed-on: https://go-review.googlesource.com/c/go/+/507535
Run-TryBot: Cuong Manh Le <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>

Author: cuonglm

src/cmd/compile/internal/walk/builtin.go

@@ -135,7 +135,11 @@ func walkClear(n *ir.UnaryExpr) ir.Node {
 	typ := n.X.Type()
 	switch {
 	case typ.IsSlice():
-		return arrayClear(n.X.Pos(), n.X, nil)
+		if n := arrayClear(n.X.Pos(), n.X, nil); n != nil {
+			return n
+		}
+		// If n == nil, we are clearing an array which takes zero memory, do nothing.
+		return ir.NewBlockStmt(n.Pos(), nil)
 	case typ.IsMap():
 		return mapClear(n.X, reflectdata.TypePtrAt(n.X.Pos(), n.X.Type()))
 	}

test/fixedbugs/issue61127.go

@@ -0,0 +1,13 @@
+// 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 main
+
+var V = []struct{}{}
+
+func main() {
+	clear(V)
+}