cmd/compile: fix defer/go calls to variadic unsafe-uintptr functions

Before generating wrapper function, turn any f(a, b, []T{c, d, e}...)
calls back into f(a, b, c, d, e). This allows the existing code for
recognizing and specially handling unsafe.Pointer->uintptr conversions
to correctly handle variadic arguments too.

Fixes #41460.

Change-Id: I0a1255abdd1bd5dafd3e89547aedd4aec878394c
Reviewed-on: https://go-review.googlesource.com/c/go/+/263297
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -3881,6 +3881,16 @@ func wrapCall(n *Node, init *Nodes) *Node {
 	}
 
 	isBuiltinCall := n.Op != OCALLFUNC && n.Op != OCALLMETH && n.Op != OCALLINTER
+
+	// Turn f(a, b, []T{c, d, e}...) back into f(a, b, c, d, e).
+	if !isBuiltinCall && n.IsDDD() {
+		last := n.List.Len() - 1
+		if va := n.List.Index(last); va.Op == OSLICELIT {
+			n.List.Set(append(n.List.Slice()[:last], va.List.Slice()...))
+			n.SetIsDDD(false)
+		}
+	}
+
 	// origArgs keeps track of what argument is uintptr-unsafe/unsafe-uintptr conversion.
 	origArgs := make([]*Node, n.List.Len())
 	t := nod(OTFUNC, nil, nil)

test/fixedbugs/issue24491a.go

@@ -34,9 +34,6 @@ func test(s string, p, q uintptr, rest ...uintptr) int {
 		panic(s + ": q failed")
 	}
 	for _, r := range rest {
-		// TODO(mdempsky): Remove.
-		break
-
 		if *(*string)(unsafe.Pointer(r)) != "ok" {
 			panic(s + ": r[i] failed")
 		}