20 files changed, 218 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/amd64/galign.go b/src/cmd/compile/internal/amd64/galign.go
index bb3830bca5..6fd7f31617 100644
--- a/src/cmd/compile/internal/amd64/galign.go
+++ b/src/cmd/compile/internal/amd64/galign.go
@@ -27,4 +27,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = ssaMarkMoves
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/amd64/ggen.go b/src/cmd/compile/internal/amd64/ggen.go
index c137b52d80..d12153383e 100644
--- a/src/cmd/compile/internal/amd64/ggen.go
+++ b/src/cmd/compile/internal/amd64/ggen.go
@@ -166,6 +166,27 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64, ax *uint32, x0 *uin
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	op := x86.AMOVQ
+	if gc.Widthptr == 4 {
+		op = x86.AMOVL
+	}
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += int64(gc.Widthptr) {
+		p := gc.AddAsmAfter(op, pp)
+		pp = p
+		p.From.Type = obj.TYPE_CONST
+		p.From.Offset = 0
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = x86.REG_SP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	// This is actually not the x86 NOP anymore,
 	// but at the point where it gets used, AX is dead
diff --git a/src/cmd/compile/internal/arm/galign.go b/src/cmd/compile/internal/arm/galign.go
index 308b016026..53f57cd978 100644
--- a/src/cmd/compile/internal/arm/galign.go
+++ b/src/cmd/compile/internal/arm/galign.go
@@ -21,4 +21,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = func(s *gc.SSAGenState, b *ssa.Block) {}
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/arm/ggen.go b/src/cmd/compile/internal/arm/ggen.go
index 6dce0a4e80..1b97a4d0c9 100644
--- a/src/cmd/compile/internal/arm/ggen.go
+++ b/src/cmd/compile/internal/arm/ggen.go
@@ -92,6 +92,27 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64, r0 *uint32) *obj.Pr
 
 	return p
 }
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	p := gc.Prog(arm.AMOVW)
+	p.From.Type = obj.TYPE_CONST
+	p.From.Offset = 0
+	p.To.Type = obj.TYPE_REG
+	p.To.Reg = arm.REGTMP
+	for i := int64(0); i < size; i += 4 {
+		p := gc.AddAsmAfter(arm.AMOVW, pp)
+		pp = p
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = arm.REGTMP
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = arm.REGSP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
 
 func ginsnop() {
 	p := gc.Prog(arm.AAND)
diff --git a/src/cmd/compile/internal/arm64/galign.go b/src/cmd/compile/internal/arm64/galign.go
index 20a67e398d..15680dd168 100644
--- a/src/cmd/compile/internal/arm64/galign.go
+++ b/src/cmd/compile/internal/arm64/galign.go
@@ -21,4 +21,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = func(s *gc.SSAGenState, b *ssa.Block) {}
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/arm64/ggen.go b/src/cmd/compile/internal/arm64/ggen.go
index 16813b642a..83966a4933 100644
--- a/src/cmd/compile/internal/arm64/ggen.go
+++ b/src/cmd/compile/internal/arm64/ggen.go
@@ -103,6 +103,23 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += 8 {
+		p := gc.AddAsmAfter(arm64.AMOVD, pp)
+		pp = p
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = arm64.REGZERO
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = arm64.REGSP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	p := gc.Prog(arm64.AHINT)
 	p.From.Type = obj.TYPE_CONST
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index ff33e9c1c4..a529ca40f7 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -361,6 +361,12 @@ type Arch struct {
 	// SSAGenBlock emits end-of-block Progs. SSAGenValue should be called
 	// for all values in the block before SSAGenBlock.
 	SSAGenBlock func(s *SSAGenState, b, next *ssa.Block)
+
+	// ZeroAuto emits code to zero the given auto stack variable.
+	// Code is added immediately after pp.
+	// ZeroAuto must not use any non-temporary registers.
+	// ZeroAuto will only be called for variables which contain a pointer.
+	ZeroAuto func(n *Node, pp *obj.Prog)
 }
 
 var pcloc int32
diff --git a/src/cmd/compile/internal/gc/gsubr.go b/src/cmd/compile/internal/gc/gsubr.go
index 1e8636347a..2a8bedff96 100644
--- a/src/cmd/compile/internal/gc/gsubr.go
+++ b/src/cmd/compile/internal/gc/gsubr.go
@@ -72,6 +72,15 @@ func Appendpp(p *obj.Prog, as obj.As, ftype obj.AddrType, freg int16, foffset in
 	return q
 }
 
+func AddAsmAfter(as obj.As, p *obj.Prog) *obj.Prog {
+	q := Ctxt.NewProg()
+	Clearp(q)
+	q.As = as
+	q.Link = p.Link
+	p.Link = q
+	return q
+}
+
 func ggloblnod(nam *Node) {
 	s := Linksym(nam.Sym)
 	s.Gotype = Linksym(ngotype(nam))
diff --git a/src/cmd/compile/internal/gc/pgen.go b/src/cmd/compile/internal/gc/pgen.go
index 643ba79d63..dde28f670b 100644
--- a/src/cmd/compile/internal/gc/pgen.go
+++ b/src/cmd/compile/internal/gc/pgen.go
@@ -120,7 +120,30 @@ func Gvarlive(n *Node) {
 }
 
 func removevardef(firstp *obj.Prog) {
+	// At VARKILLs, zero variable if it is ambiguously live.
+	// After the VARKILL anything this variable references
+	// might be collected. If it were to become live again later,
+	// the GC will see references to already-collected objects.
+	// See issue 20029.
 	for p := firstp; p != nil; p = p.Link {
+		if p.As != obj.AVARKILL {
+			continue
+		}
+		n := p.To.Node.(*Node)
+		if !n.Name.Needzero {
+			continue
+		}
+		if n.Class != PAUTO {
+			Fatalf("zero of variable which isn't PAUTO %v", n)
+		}
+		if n.Type.Size()%int64(Widthptr) != 0 {
+			Fatalf("zero of variable not a multiple of ptr size %v", n)
+		}
+		Thearch.ZeroAuto(n, p)
+	}
+
+	for p := firstp; p != nil; p = p.Link {
+
 		for p.Link != nil && (p.Link.As == obj.AVARDEF || p.Link.As == obj.AVARKILL || p.Link.As == obj.AVARLIVE) {
 			p.Link = p.Link.Link
 		}
diff --git a/src/cmd/compile/internal/mips/galign.go b/src/cmd/compile/internal/mips/galign.go
index 39f5d2bf64..e6d117a806 100644
--- a/src/cmd/compile/internal/mips/galign.go
+++ b/src/cmd/compile/internal/mips/galign.go
@@ -23,4 +23,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = func(s *gc.SSAGenState, b *ssa.Block) {}
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/mips/ggen.go b/src/cmd/compile/internal/mips/ggen.go
index ec540f8102..a95db57ffe 100644
--- a/src/cmd/compile/internal/mips/ggen.go
+++ b/src/cmd/compile/internal/mips/ggen.go
@@ -92,6 +92,23 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += 4 {
+		p := gc.AddAsmAfter(mips.AMOVW, pp)
+		pp = p
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = mips.REGZERO
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = mips.REGSP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	p := gc.Prog(mips.ANOR)
 	p.From.Type = obj.TYPE_REG
diff --git a/src/cmd/compile/internal/mips64/galign.go b/src/cmd/compile/internal/mips64/galign.go
index 4a36a4ce5b..e8ea073057 100644
--- a/src/cmd/compile/internal/mips64/galign.go
+++ b/src/cmd/compile/internal/mips64/galign.go
@@ -25,4 +25,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = func(s *gc.SSAGenState, b *ssa.Block) {}
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/mips64/ggen.go b/src/cmd/compile/internal/mips64/ggen.go
index 2af4a8b1ce..eb48e2b261 100644
--- a/src/cmd/compile/internal/mips64/ggen.go
+++ b/src/cmd/compile/internal/mips64/ggen.go
@@ -95,6 +95,23 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += 8 {
+		p := gc.AddAsmAfter(mips.AMOVV, pp)
+		pp = p
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = mips.REGZERO
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = mips.REGSP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	p := gc.Prog(mips.ANOR)
 	p.From.Type = obj.TYPE_REG
diff --git a/src/cmd/compile/internal/ppc64/galign.go b/src/cmd/compile/internal/ppc64/galign.go
index 186aa2946a..3780247731 100644
--- a/src/cmd/compile/internal/ppc64/galign.go
+++ b/src/cmd/compile/internal/ppc64/galign.go
@@ -24,6 +24,7 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = ssaMarkMoves
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 
 	initvariants()
 	initproginfo()
diff --git a/src/cmd/compile/internal/ppc64/ggen.go b/src/cmd/compile/internal/ppc64/ggen.go
index b3ce968567..4abd18dc3d 100644
--- a/src/cmd/compile/internal/ppc64/ggen.go
+++ b/src/cmd/compile/internal/ppc64/ggen.go
@@ -90,6 +90,23 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += 8 {
+		p := gc.AddAsmAfter(ppc64.AMOVD, pp)
+		pp = p
+		p.From.Type = obj.TYPE_REG
+		p.From.Reg = ppc64.REGZERO
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = ppc64.REGSP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	p := gc.Prog(ppc64.AOR)
 	p.From.Type = obj.TYPE_REG
diff --git a/src/cmd/compile/internal/s390x/galign.go b/src/cmd/compile/internal/s390x/galign.go
index 91b9ed0777..9424d204fa 100644
--- a/src/cmd/compile/internal/s390x/galign.go
+++ b/src/cmd/compile/internal/s390x/galign.go
@@ -20,4 +20,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = ssaMarkMoves
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/s390x/ggen.go b/src/cmd/compile/internal/s390x/ggen.go
index 15c65546d6..5ecfaa5177 100644
--- a/src/cmd/compile/internal/s390x/ggen.go
+++ b/src/cmd/compile/internal/s390x/ggen.go
@@ -143,6 +143,19 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64) *obj.Prog {
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	p := gc.AddAsmAfter(s390x.ACLEAR, pp)
+	pp = p
+	p.From.Type = obj.TYPE_CONST
+	p.From.Offset = n.Type.Size()
+	p.To.Type = obj.TYPE_MEM
+	p.To.Name = obj.NAME_AUTO
+	p.To.Reg = s390x.REGSP
+	p.To.Offset = n.Xoffset
+	p.To.Sym = gc.Linksym(n.Sym)
+}
+
 func ginsnop() {
 	p := gc.Prog(s390x.AOR)
 	p.From.Type = obj.TYPE_REG
diff --git a/src/cmd/compile/internal/x86/galign.go b/src/cmd/compile/internal/x86/galign.go
index edac6a002a..bb29d2a02f 100644
--- a/src/cmd/compile/internal/x86/galign.go
+++ b/src/cmd/compile/internal/x86/galign.go
@@ -31,4 +31,5 @@ func Init() {
 	gc.Thearch.SSAMarkMoves = ssaMarkMoves
 	gc.Thearch.SSAGenValue = ssaGenValue
 	gc.Thearch.SSAGenBlock = ssaGenBlock
+	gc.Thearch.ZeroAuto = zeroAuto
 }
diff --git a/src/cmd/compile/internal/x86/ggen.go b/src/cmd/compile/internal/x86/ggen.go
index 25769b4de0..33ffc5f534 100644
--- a/src/cmd/compile/internal/x86/ggen.go
+++ b/src/cmd/compile/internal/x86/ggen.go
@@ -84,6 +84,23 @@ func zerorange(p *obj.Prog, frame int64, lo int64, hi int64, ax *uint32) *obj.Pr
 	return p
 }
 
+func zeroAuto(n *gc.Node, pp *obj.Prog) {
+	// Note: this code must not clobber any registers.
+	sym := gc.Linksym(n.Sym)
+	size := n.Type.Size()
+	for i := int64(0); i < size; i += 4 {
+		p := gc.AddAsmAfter(x86.AMOVL, pp)
+		pp = p
+		p.From.Type = obj.TYPE_CONST
+		p.From.Offset = 0
+		p.To.Type = obj.TYPE_MEM
+		p.To.Name = obj.NAME_AUTO
+		p.To.Reg = x86.REG_SP
+		p.To.Offset = n.Xoffset + i
+		p.To.Sym = sym
+	}
+}
+
 func ginsnop() {
 	p := gc.Prog(x86.AXCHGL)
 	p.From.Type = obj.TYPE_REG
diff --git a/test/fixedbugs/issue20029.go b/test/fixedbugs/issue20029.go
new file mode 100644
index 0000000000..db3f8aa5dd
--- /dev/null
+++ b/test/fixedbugs/issue20029.go
@@ -0,0 +1,32 @@
+// run
+
+// Copyright 2017 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 20029: make sure we zero at VARKILLs of
+// ambiguously live variables.
+// The ambiguously live variable here is the hiter
+// for the inner range loop.
+
+package main
+
+import "runtime"
+
+func f(m map[int]int) {
+outer:
+	for i := 0; i < 10; i++ {
+		for k := range m {
+			if k == 5 {
+				continue outer
+			}
+		}
+		runtime.GC()
+		break
+	}
+	runtime.GC()
+}
+func main() {
+	m := map[int]int{1: 2, 2: 3, 3: 4}
+	f(m)
+}