cmd/compile/internal/ppc64: fix the epilogue for non-leaf generated methods

This lets us re-enable duffzero.

Fixes #12108

Change-Id: Iefd24d26eaa56067caa2c29ff99cd20a42d8714a
Reviewed-on: https://go-review.googlesource.com/14937
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ppc64/ggen.go

@@ -71,10 +71,7 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 		for i := int64(0); i < cnt; i += int64(gc.Widthptr) {
 			p = appendpp(p, ppc64.AMOVD, obj.TYPE_REG, ppc64.REGZERO, 0, obj.TYPE_MEM, ppc64.REGSP, 8+frame+lo+i)
 		}
-		// TODO(dfc): https://golang.org/issue/12108
-		// If DUFFZERO is used inside a tail call (see genwrapper) it will
-		// overwrite the link register.
-	} else if false && cnt <= int64(128*gc.Widthptr) {
+	} else if cnt <= int64(128*gc.Widthptr) {
 		p = appendpp(p, ppc64.AADD, obj.TYPE_CONST, 0, 8+frame+lo-8, obj.TYPE_REG, ppc64.REGRT1, 0)
 		p.Reg = ppc64.REGSP
 		p = appendpp(p, obj.ADUFFZERO, obj.TYPE_NONE, 0, 0, obj.TYPE_MEM, 0, 0)
@@ -443,10 +440,7 @@ func clearfat(nl *gc.Node) {
 
 		// The loop leaves R3 on the last zeroed dword
 		boff = 8
-		// TODO(dfc): https://golang.org/issue/12108
-		// If DUFFZERO is used inside a tail call (see genwrapper) it will
-		// overwrite the link register.
-	} else if false && q >= 4 {
+	} else if q >= 4 {
 		p := gins(ppc64.ASUB, nil, &dst)
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = 8

src/cmd/internal/obj/ppc64/obj9.go

@@ -473,18 +473,19 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 				break
 			}
 
-			if p.To.Sym != nil { // retjmp
-				p.As = ABR
-				p.To.Type = obj.TYPE_BRANCH
-				break
-			}
+			retTarget := p.To.Sym
 
 			if cursym.Text.Mark&LEAF != 0 {
 				if autosize == 0 {
 					p.As = ABR
 					p.From = obj.Addr{}
-					p.To.Type = obj.TYPE_REG
-					p.To.Reg = REG_LR
+					if retTarget == nil {
+						p.To.Type = obj.TYPE_REG
+						p.To.Reg = REG_LR
+					} else {
+						p.To.Type = obj.TYPE_BRANCH
+						p.To.Sym = retTarget
+					}
 					p.Mark |= BRANCH
 					break
 				}
@@ -562,14 +563,18 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 			q1 = ctxt.NewProg()
 			q1.As = ABR
 			q1.Lineno = p.Lineno
-			q1.To.Type = obj.TYPE_REG
-			q1.To.Reg = REG_LR
+			if retTarget == nil {
+				q1.To.Type = obj.TYPE_REG
+				q1.To.Reg = REG_LR
+			} else {
+				q1.To.Type = obj.TYPE_BRANCH
+				q1.To.Sym = retTarget
+			}
 			q1.Mark |= BRANCH
 			q1.Spadj = +autosize
 
 			q1.Link = q.Link
 			q.Link = q1
-
 		case AADD:
 			if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.From.Type == obj.TYPE_CONST {
 				p.Spadj = int32(-p.From.Offset)

test/fixedbugs/issue12108.go

@@ -0,0 +1,37 @@
+// run
+
+// Copyright 2015 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.
+
+// A generated method with a return value large enough to be
+// initialized by duffzero is not a leaf method, which violated
+// assumptions made by cmd/internal/obj/ppc64.
+
+package main
+
+const N = 9 // values > 8 cause (Super).Method to use duffzero
+
+type Base struct {
+}
+
+func (b *Base) Method() (x [N]uintptr) {
+	return
+}
+
+type Super struct {
+	Base
+}
+
+type T interface {
+	Method() [N]uintptr
+}
+
+func f(q T) {
+	q.Method()
+}
+
+func main() {
+	var s Super
+	f(&s)
+}