cmd/compile: copy literals when inlining

Without this, literals keep their original source positions through
inlining, which results in strange jumps in line numbers of inlined
function bodies. By copying literals, inlining can update their source
position like other nodes.

Fixes #15453.

Change-Id: Iad5d9bbfe183883794213266dc30e31bab89ee69
Reviewed-on: https://go-review.googlesource.com/37232
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -977,7 +977,12 @@ func (subst *inlsubst) node(n *Node) *Node {
 		return n
 
 	case OLITERAL, OTYPE:
-		return n
+		// If n is a named constant or type, we can continue
+		// using it in the inline copy. Otherwise, make a copy
+		// so we can update the line number.
+		if n.Sym != nil {
+			return n
+		}
 
 		// Since we don't handle bodies with closures, this return is guaranteed to belong to the current inlined function.
 
@@ -1014,25 +1019,25 @@ func (subst *inlsubst) node(n *Node) *Node {
 		p := fmt.Sprintf("%s·%d", n.Left.Sym.Name, inlgen)
 		m.Left = newname(lookup(p))
 
-		return m
-	default:
-		m := nod(OXXX, nil, nil)
-		*m = *n
-		m.Ninit.Set(nil)
-
-		if n.Op == OCLOSURE {
-			Fatalf("cannot inline function containing closure: %+v", n)
-		}
-
-		m.Left = subst.node(n.Left)
-		m.Right = subst.node(n.Right)
-		m.List.Set(subst.list(n.List))
-		m.Rlist.Set(subst.list(n.Rlist))
-		m.Ninit.Set(append(m.Ninit.Slice(), subst.list(n.Ninit)...))
-		m.Nbody.Set(subst.list(n.Nbody))
-
 		return m
 	}
+
+	m := nod(OXXX, nil, nil)
+	*m = *n
+	m.Ninit.Set(nil)
+
+	if n.Op == OCLOSURE {
+		Fatalf("cannot inline function containing closure: %+v", n)
+	}
+
+	m.Left = subst.node(n.Left)
+	m.Right = subst.node(n.Right)
+	m.List.Set(subst.list(n.List))
+	m.Rlist.Set(subst.list(n.Rlist))
+	m.Ninit.Set(append(m.Ninit.Slice(), subst.list(n.Ninit)...))
+	m.Nbody.Set(subst.list(n.Nbody))
+
+	return m
 }
 
 // setPos is a visitor to update position info with a new inlining index.
@@ -1051,6 +1056,12 @@ func (s *setPos) node(n *Node) {
 	if n == nil {
 		return
 	}
+	if n.Op == OLITERAL || n.Op == OTYPE {
+		if n.Sym != nil {
+			// This node is not a copy, so don't clobber position.
+			return
+		}
+	}
 
 	// don't clobber names, unless they're freshly synthesized
 	if n.Op != ONAME || !n.Pos.IsKnown() {

test/inline_literal.go

@@ -0,0 +1,50 @@
+// 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.
+
+package main
+
+import (
+	"log"
+	"reflect"
+	"runtime"
+)
+
+func hello() string {
+	return "Hello World" // line 16
+}
+
+func foo() string { // line 19
+	x := hello() // line 20
+	y := hello() // line 21
+	return x + y // line 22
+}
+
+func bar() string {
+	x := hello() // line 26
+	return x
+}
+
+// funcPC returns the PC for the func value f.
+func funcPC(f interface{}) uintptr {
+	return reflect.ValueOf(f).Pointer()
+}
+
+// Test for issue #15453. Previously, line 26 would appear in foo().
+func main() {
+	pc := funcPC(foo)
+	f := runtime.FuncForPC(pc)
+	for ; runtime.FuncForPC(pc) == f; pc++ {
+		file, line := f.FileLine(pc)
+		if line == 0 {
+			continue
+		}
+		// Line 16 can appear inside foo() because PC-line table has
+		// innermost line numbers after inlining.
+		if line != 16 && !(line >= 19 && line <= 22) {
+			log.Fatalf("unexpected line at PC=%d: %s:%d\n", pc, file, line)
+		}
+	}
+}