cmd/gc: save local var list before inlining

This avoids problems with inlining in genwrappers, which
occurs after functions have been compiled.  Compiling a
function may cause some unused local vars to be removed from
the list.  Since a local var may be unused due to
optimization, it is possible that a removed local var winds up
beingused in the inlined version, in which case hilarity
ensues.

Fixes #5515.

R=golang-dev, khr, dave
CC=golang-dev
https://golang.org/cl/10210043

src/cmd/gc/go.h

@@ -284,6 +284,7 @@ struct	Node
 	NodeList*	cvars;	// closure params
 	NodeList*	dcl;	// autodcl for this func/closure
 	NodeList*	inl;	// copy of the body for use in inlining
+	NodeList*	inldcl;	// copy of dcl for use in inlining
 
 	// OLITERAL/OREGISTER
 	Val	val;

src/cmd/gc/inl.c

@@ -146,6 +146,7 @@ caninl(Node *fn)
 
 	fn->nname->inl = fn->nbody;
 	fn->nbody = inlcopylist(fn->nname->inl);
+	fn->nname->inldcl = inlcopylist(fn->nname->defn->dcl);
 
 	// hack, TODO, check for better way to link method nodes back to the thing with the ->inl
 	// this is so export can find the body of a method
@@ -559,8 +560,8 @@ mkinlcall1(Node **np, Node *fn, int isddd)
 
 //dumplist("ninit pre", ninit);
 
-	if (fn->defn) // local function
-		dcl = fn->defn->dcl;
+	if(fn->defn) // local function
+		dcl = fn->inldcl;
 	else // imported function
 		dcl = fn->dcl;
 

test/fixedbugs/issue5515.go

+// run
+
+// Copyright 2013 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.
+
+// issue 5515: miscompilation doing inlining in generated method wrapper
+
+package main
+
+type T uint32
+
+func main() {
+        b := make([]T, 8)
+        b[0] = 0xdeadbeef
+        rs := Slice(b)
+        sort(rs)
+}
+
+type Slice []T
+
+func (s Slice) Swap(i, j int) {
+        tmp := s[i]
+        s[i] = s[j]
+        s[j] = tmp
+}
+
+type Interface interface {
+        Swap(i, j int)
+}
+
+func sort(data Interface) {
+        data.Swap(0, 4)
+}