From: Robert Griesemer <gri@golang.org>
Date: Thu, 8 Dec 2016 00:02:42 +0000 (-0800)
Subject: [dev.inline] cmd/internal/src: make Pos implementation abstract
X-Git-Tag: go1.9beta1~1833^2~21
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=82d0caea2c5041a0d0260ff5ec7f7b61ee2bb0af;p=gostls13.git

[dev.inline] cmd/internal/src: make Pos implementation abstract

Adjust cmd/compile accordingly.

This will make it easier to replace the underlying implementation.

Change-Id: I33645850bb18c839b24785b6222a9e028617addb
Reviewed-on: https://go-review.googlesource.com/34133
Reviewed-by: David Lazar <lazard@golang.org>
---

diff --git a/src/cmd/compile/fmt_test.go b/src/cmd/compile/fmt_test.go
index 2490e37e24..1a648084f7 100644
--- a/src/cmd/compile/fmt_test.go
+++ b/src/cmd/compile/fmt_test.go
@@ -654,7 +654,6 @@ var knownFormats = map[string]string{
 	"cmd/compile/internal/syntax.token %q":            "",
 	"cmd/compile/internal/syntax.token %s":            "",
 	"cmd/internal/obj.As %v":                          "",
-	"cmd/internal/src.Pos %d":                         "",
 	"error %v":                                        "",
 	"float64 %.2f":                                    "",
 	"float64 %.3f":                                    "",
diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go
index 3c997f20ae..98ea7cadf1 100644
--- a/src/cmd/compile/internal/amd64/ssa.go
+++ b/src/cmd/compile/internal/amd64/ssa.go
@@ -875,7 +875,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.To.Type = obj.TYPE_MEM
 		p.To.Reg = v.Args[0].Reg()
 		gc.AddAux(&p.To, v)
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line.Line()==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpAMD64MOVLatomicload, ssa.OpAMD64MOVQatomicload:
diff --git a/src/cmd/compile/internal/arm/ssa.go b/src/cmd/compile/internal/arm/ssa.go
index 5a69ed3c3b..799d395208 100644
--- a/src/cmd/compile/internal/arm/ssa.go
+++ b/src/cmd/compile/internal/arm/ssa.go
@@ -705,7 +705,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = arm.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line.Line()==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpARMLoweredZero:
diff --git a/src/cmd/compile/internal/arm64/ssa.go b/src/cmd/compile/internal/arm64/ssa.go
index 5670ef8e96..47976eb91b 100644
--- a/src/cmd/compile/internal/arm64/ssa.go
+++ b/src/cmd/compile/internal/arm64/ssa.go
@@ -690,7 +690,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = arm64.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpVarDef:
diff --git a/src/cmd/compile/internal/gc/alg.go b/src/cmd/compile/internal/gc/alg.go
index 8113710e39..50b75aa09f 100644
--- a/src/cmd/compile/internal/gc/alg.go
+++ b/src/cmd/compile/internal/gc/alg.go
@@ -4,7 +4,10 @@
 
 package gc
 
-import "fmt"
+import (
+	"cmd/internal/src"
+	"fmt"
+)
 
 // AlgKind describes the kind of algorithms used for comparing and
 // hashing a Type.
@@ -186,7 +189,7 @@ func genhash(sym *Sym, t *Type) {
 		fmt.Printf("genhash %v %v\n", sym, t)
 	}
 
-	lineno = 1 // less confusing than end of input
+	lineno = src.MakePos(1) // less confusing than end of input
 	dclcontext = PEXTERN
 	markdcl()
 
@@ -362,7 +365,7 @@ func geneq(sym *Sym, t *Type) {
 		fmt.Printf("geneq %v %v\n", sym, t)
 	}
 
-	lineno = 1 // less confusing than end of input
+	lineno = src.MakePos(1) // less confusing than end of input
 	dclcontext = PEXTERN
 	markdcl()
 
diff --git a/src/cmd/compile/internal/gc/bexport.go b/src/cmd/compile/internal/gc/bexport.go
index 1da5b699a4..c87ab9fb13 100644
--- a/src/cmd/compile/internal/gc/bexport.go
+++ b/src/cmd/compile/internal/gc/bexport.go
@@ -591,7 +591,7 @@ func (p *exporter) pos(n *Node) {
 
 func fileLine(n *Node) (file string, line int) {
 	if n != nil {
-		file, line = Ctxt.LineHist.AbsFileLine(int(n.Lineno))
+		file, line = Ctxt.LineHist.AbsFileLine(int(n.Lineno.Line()))
 	}
 	return
 }
diff --git a/src/cmd/compile/internal/gc/dcl.go b/src/cmd/compile/internal/gc/dcl.go
index 460764af3a..4f2254e689 100644
--- a/src/cmd/compile/internal/gc/dcl.go
+++ b/src/cmd/compile/internal/gc/dcl.go
@@ -114,7 +114,7 @@ func testdclstack() {
 
 // redeclare emits a diagnostic about symbol s being redeclared somewhere.
 func redeclare(s *Sym, where string) {
-	if s.Lastlineno == 0 {
+	if !s.Lastlineno.IsKnown() {
 		var tmp string
 		if s.Origpkg != nil {
 			tmp = s.Origpkg.Path
@@ -288,7 +288,7 @@ func variter(vl []*Node, t *Node, el []*Node) []*Node {
 // declare constants from grammar
 // new_name_list [[type] = expr_list]
 func constiter(vl []*Node, t *Node, cl []*Node) []*Node {
-	lno := src.Pos(0) // default is to leave line number alone in listtreecopy
+	var lno src.Pos // default is to leave line number alone in listtreecopy
 	if len(cl) == 0 {
 		if t != nil {
 			yyerror("const declaration cannot have type without expression")
@@ -719,7 +719,7 @@ func checkembeddedtype(t *Type) {
 
 	if t.IsPtr() || t.IsUnsafePtr() {
 		yyerror("embedded type cannot be a pointer")
-	} else if t.Etype == TFORW && t.ForwardType().Embedlineno == 0 {
+	} else if t.Etype == TFORW && !t.ForwardType().Embedlineno.IsKnown() {
 		t.ForwardType().Embedlineno = lineno
 	}
 }
@@ -1355,7 +1355,7 @@ func checknowritebarrierrec() {
 	visitBottomUp(xtop, func(list []*Node, recursive bool) {
 		// Functions with write barriers have depth 0.
 		for _, n := range list {
-			if n.Func.WBLineno != 0 && n.Func.Pragma&Yeswritebarrierrec == 0 {
+			if n.Func.WBLineno.IsKnown() && n.Func.Pragma&Yeswritebarrierrec == 0 {
 				c.best[n] = nowritebarrierrecCall{target: nil, depth: 0, lineno: n.Func.WBLineno}
 			}
 		}
@@ -1373,7 +1373,7 @@ func checknowritebarrierrec() {
 					// yeswritebarrierrec function.
 					continue
 				}
-				if n.Func.WBLineno == 0 {
+				if !n.Func.WBLineno.IsKnown() {
 					c.curfn = n
 					c.visitcodelist(n.Nbody)
 				}
diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index fffce440bc..53889be531 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -283,8 +283,8 @@ func (n *Node) jconv(s fmt.State, flag FmtFlag) {
 		fmt.Fprintf(s, " g(%d)", n.Name.Vargen)
 	}
 
-	if n.Lineno != 0 {
-		fmt.Fprintf(s, " l(%d)", n.Lineno)
+	if n.Lineno.IsKnown() {
+		fmt.Fprintf(s, " l(%d)", n.Lineno.Line())
 	}
 
 	if c == 0 && n.Xoffset != BADWIDTH {
diff --git a/src/cmd/compile/internal/gc/gsubr.go b/src/cmd/compile/internal/gc/gsubr.go
index c2784cd6af..3a3effec2f 100644
--- a/src/cmd/compile/internal/gc/gsubr.go
+++ b/src/cmd/compile/internal/gc/gsubr.go
@@ -40,12 +40,12 @@ func Prog(as obj.As) *obj.Prog {
 	Clearp(pc)
 	p.Link = pc
 
-	if lineno == 0 && Debug['K'] != 0 {
-		Warn("prog: line 0")
+	if !lineno.IsKnown() && Debug['K'] != 0 {
+		Warn("prog: unknown position (line 0)")
 	}
 
 	p.As = as
-	p.Lineno = int32(lineno) // TODO(gri) fix this
+	p.Lineno = int32(lineno.Line()) // TODO(gri) fix this
 	return p
 }
 
diff --git a/src/cmd/compile/internal/gc/inl.go b/src/cmd/compile/internal/gc/inl.go
index bdca1b1d76..1fe25fa15e 100644
--- a/src/cmd/compile/internal/gc/inl.go
+++ b/src/cmd/compile/internal/gc/inl.go
@@ -1029,7 +1029,7 @@ func setlno(n *Node, lno src.Pos) {
 	}
 
 	// don't clobber names, unless they're freshly synthesized
-	if n.Op != ONAME || n.Lineno == 0 {
+	if n.Op != ONAME || !n.Lineno.IsKnown() {
 		n.Lineno = lno
 	}
 
diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index 4ed7f1c5dc..0fdb862c28 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -300,7 +300,7 @@ func Main() {
 	blockgen = 1
 	dclcontext = PEXTERN
 	nerrors = 0
-	lexlineno = 1
+	lexlineno = src.MakePos(1)
 
 	timings.Start("fe", "loadsys")
 	loadsys()
@@ -320,11 +320,11 @@ func Main() {
 		// Instead of converting EOF into '\n' in getc and count it as an extra line
 		// for the line history to work, and which then has to be corrected elsewhere,
 		// just add a line here.
-		lexlineno++
+		lexlineno = src.MakePos(lexlineno.Line() + 1)
 		linehistpop()
 	}
 	timings.Stop()
-	timings.AddEvent(int64(lexlineno-lexlineno0), "lines")
+	timings.AddEvent(int64(lexlineno.Line()-lexlineno0.Line()), "lines")
 
 	testdclstack()
 	mkpackage(localpkg.Name) // final import not used checks
diff --git a/src/cmd/compile/internal/gc/noder.go b/src/cmd/compile/internal/gc/noder.go
index 8d3babc544..e52b0c7511 100644
--- a/src/cmd/compile/internal/gc/noder.go
+++ b/src/cmd/compile/internal/gc/noder.go
@@ -22,7 +22,7 @@ func parseFile(filename string) {
 	}
 	defer src.Close()
 
-	p := noder{baseline: lexlineno}
+	p := noder{baseline: lexlineno.Line()}
 	file, _ := syntax.Parse(src, p.error, p.pragma, 0) // errors are tracked via p.error
 
 	p.file(file)
@@ -40,7 +40,7 @@ func parseFile(filename string) {
 
 // noder transforms package syntax's AST into a Nod tree.
 type noder struct {
-	baseline  src.Pos
+	baseline  int32
 	linknames []int // tracks //go:linkname lines
 }
 
@@ -50,7 +50,7 @@ func (p *noder) file(file *syntax.File) {
 
 	xtop = append(xtop, p.decls(file.DeclList)...)
 
-	lexlineno = p.baseline + src.Pos(file.Lines) - 1
+	lexlineno = src.MakePos(p.baseline + int32(file.Lines) - 1)
 	lineno = lexlineno
 }
 
@@ -231,7 +231,7 @@ func (p *noder) funcDecl(fun *syntax.FuncDecl) *Node {
 		yyerror("can only use //go:noescape with external func implementations")
 	}
 	f.Func.Pragma = pragma
-	lineno = p.baseline + src.Pos(fun.EndLine) - 1
+	lineno = src.MakePos(p.baseline + int32(fun.EndLine) - 1)
 	f.Func.Endlineno = lineno
 
 	funcbody(f)
@@ -357,14 +357,14 @@ func (p *noder) expr(expr syntax.Expr) *Node {
 			l[i] = p.wrapname(expr.ElemList[i], e)
 		}
 		n.List.Set(l)
-		lineno = p.baseline + src.Pos(expr.EndLine) - 1
+		lineno = src.MakePos(p.baseline + int32(expr.EndLine) - 1)
 		return n
 	case *syntax.KeyValueExpr:
 		return p.nod(expr, OKEY, p.expr(expr.Key), p.wrapname(expr.Value, p.expr(expr.Value)))
 	case *syntax.FuncLit:
 		closurehdr(p.typeExpr(expr.Type))
 		body := p.stmts(expr.Body)
-		lineno = p.baseline + src.Pos(expr.EndLine) - 1
+		lineno = src.MakePos(p.baseline + int32(expr.EndLine) - 1)
 		return p.setlineno(expr, closurebody(body))
 	case *syntax.ParenExpr:
 		return p.nod(expr, OPAREN, p.expr(expr.X), nil)
@@ -986,12 +986,12 @@ func (p *noder) nod(orig syntax.Node, op Op, left, right *Node) *Node {
 }
 
 func (p *noder) setlineno(src_ syntax.Node, dst *Node) *Node {
-	l := src.Pos(src_.Line())
+	l := src_.Line()
 	if l == 0 {
 		// TODO(mdempsky): Shouldn't happen. Fix package syntax.
 		return dst
 	}
-	dst.Lineno = p.baseline + l - 1
+	dst.Lineno = src.MakePos(p.baseline + int32(l) - 1)
 	return dst
 }
 
@@ -999,24 +999,24 @@ func (p *noder) lineno(n syntax.Node) {
 	if n == nil {
 		return
 	}
-	l := src.Pos(n.Line())
+	l := n.Line()
 	if l == 0 {
 		// TODO(mdempsky): Shouldn't happen. Fix package syntax.
 		return
 	}
-	lineno = p.baseline + l - 1
+	lineno = src.MakePos(p.baseline + int32(l) - 1)
 }
 
 func (p *noder) error(err error) {
 	line := p.baseline
 	var msg string
 	if err, ok := err.(syntax.Error); ok {
-		line += src.Pos(err.Line) - 1
+		line += int32(err.Line) - 1
 		msg = err.Msg
 	} else {
 		msg = err.Error()
 	}
-	yyerrorl(line, "%s", msg)
+	yyerrorl(src.MakePos(line), "%s", msg)
 }
 
 func (p *noder) pragma(pos, line int, text string) syntax.Pragma {
@@ -1039,7 +1039,7 @@ func (p *noder) pragma(pos, line int, text string) syntax.Pragma {
 		if n <= 0 {
 			break
 		}
-		lexlineno = p.baseline + src.Pos(line)
+		lexlineno = src.MakePos(p.baseline + int32(line))
 		linehistupdate(text[5:i], n)
 
 	case strings.HasPrefix(text, "go:linkname "):
diff --git a/src/cmd/compile/internal/gc/order.go b/src/cmd/compile/internal/gc/order.go
index e3d65e5e9d..433a89d0d1 100644
--- a/src/cmd/compile/internal/gc/order.go
+++ b/src/cmd/compile/internal/gc/order.go
@@ -5,6 +5,7 @@
 package gc
 
 import (
+	"cmd/internal/src"
 	"fmt"
 )
 
@@ -510,7 +511,7 @@ func orderstmt(n *Node, order *Order) {
 
 		n.Left = orderexpr(n.Left, order, nil)
 		n.Left = ordersafeexpr(n.Left, order)
-		tmp1 := treecopy(n.Left, 0)
+		tmp1 := treecopy(n.Left, src.Pos{})
 		if tmp1.Op == OINDEXMAP {
 			tmp1.Etype = 0 // now an rvalue not an lvalue
 		}
diff --git a/src/cmd/compile/internal/gc/plive.go b/src/cmd/compile/internal/gc/plive.go
index a6f3735bdf..4cb829cc73 100644
--- a/src/cmd/compile/internal/gc/plive.go
+++ b/src/cmd/compile/internal/gc/plive.go
@@ -1254,7 +1254,7 @@ func livenessepilogue(lv *Liveness) {
 						if !n.Name.Needzero {
 							n.Name.Needzero = true
 							if debuglive >= 1 {
-								Warnl(src.Pos(p.Lineno), "%v: %L is ambiguously live", Curfn.Func.Nname, n)
+								Warnl(src.MakePos(p.Lineno), "%v: %L is ambiguously live", Curfn.Func.Nname, n)
 							}
 						}
 					}
@@ -1345,7 +1345,7 @@ func livenessepilogue(lv *Liveness) {
 						}
 						n := lv.vars[j]
 						if n.Class != PPARAM {
-							yyerrorl(src.Pos(p.Lineno), "internal error: %v %L recorded as live on entry, p.Pc=%v", Curfn.Func.Nname, n, p.Pc)
+							yyerrorl(src.MakePos(p.Lineno), "internal error: %v %L recorded as live on entry, p.Pc=%v", Curfn.Func.Nname, n, p.Pc)
 						}
 					}
 				}
diff --git a/src/cmd/compile/internal/gc/racewalk.go b/src/cmd/compile/internal/gc/racewalk.go
index bfb82b91b2..f4a02f3553 100644
--- a/src/cmd/compile/internal/gc/racewalk.go
+++ b/src/cmd/compile/internal/gc/racewalk.go
@@ -5,6 +5,7 @@
 package gc
 
 import (
+	"cmd/internal/src"
 	"fmt"
 	"strings"
 )
@@ -495,7 +496,7 @@ func callinstr(np **Node, init *Nodes, wr int, skip int) bool {
 			*np = n
 		}
 
-		n = treecopy(n, 0)
+		n = treecopy(n, src.Pos{})
 		makeaddable(n)
 		var f *Node
 		if flag_msan {
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 8df8adee59..ae0f49bd63 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -54,7 +54,7 @@ func buildssa(fn *Node) *ssa.Func {
 		s.noWB = true
 	}
 	defer func() {
-		if s.WBLineno != 0 {
+		if s.WBLineno.IsKnown() {
 			fn.Func.WBLineno = s.WBLineno
 		}
 	}()
@@ -332,12 +332,12 @@ func (s *state) endBlock() *ssa.Block {
 
 // pushLine pushes a line number on the line number stack.
 func (s *state) pushLine(line src.Pos) {
-	if line == 0 {
+	if !line.IsKnown() {
 		// the frontend may emit node with line number missing,
 		// use the parent line number in this case.
 		line = s.peekLine()
 		if Debug['K'] != 0 {
-			Warn("buildssa: line 0")
+			Warn("buildssa: unknown position (line 0)")
 		}
 	}
 	s.line = append(s.line, line)
@@ -3263,7 +3263,7 @@ func canSSAType(t *Type) bool {
 func (s *state) exprPtr(n *Node, bounded bool, lineno src.Pos) *ssa.Value {
 	p := s.expr(n)
 	if bounded || n.NonNil {
-		if s.f.Config.Debug_checknil() && lineno > 1 {
+		if s.f.Config.Debug_checknil() && lineno.Line() > 1 {
 			s.f.Config.Warnl(lineno, "removed nil check")
 		}
 		return p
@@ -3426,7 +3426,7 @@ func (s *state) insertWBmove(t *Type, left, right *ssa.Value, line src.Pos, righ
 	if s.noWB {
 		s.Error("write barrier prohibited")
 	}
-	if s.WBLineno == 0 {
+	if !s.WBLineno.IsKnown() {
 		s.WBLineno = left.Line
 	}
 
@@ -3467,7 +3467,7 @@ func (s *state) insertWBstore(t *Type, left, right *ssa.Value, line src.Pos, ski
 	if s.noWB {
 		s.Error("write barrier prohibited")
 	}
-	if s.WBLineno == 0 {
+	if !s.WBLineno.IsKnown() {
 		s.WBLineno = left.Line
 	}
 	s.storeTypeScalars(t, left, right, skip)
diff --git a/src/cmd/compile/internal/gc/subr.go b/src/cmd/compile/internal/gc/subr.go
index 49bb92beac..f4a5cc97d9 100644
--- a/src/cmd/compile/internal/gc/subr.go
+++ b/src/cmd/compile/internal/gc/subr.go
@@ -56,7 +56,7 @@ func adderr(line src.Pos, format string, args ...interface{}) {
 type byLineno []Error
 
 func (x byLineno) Len() int           { return len(x) }
-func (x byLineno) Less(i, j int) bool { return x[i].lineno < x[j].lineno }
+func (x byLineno) Less(i, j int) bool { return x[i].lineno.Before(x[j].lineno) }
 func (x byLineno) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
 
 // flusherrors sorts errors seen so far by line number, prints them to stdout,
@@ -87,7 +87,7 @@ func hcrash() {
 }
 
 func linestr(line src.Pos) string {
-	return Ctxt.Line(int(line))
+	return Ctxt.Line(int(line.Line()))
 }
 
 // lasterror keeps track of the most recently issued error.
@@ -184,21 +184,21 @@ func linehistpush(file string) {
 	if Debug['i'] != 0 {
 		fmt.Printf("import %s at line %v\n", file, linestr(lexlineno))
 	}
-	Ctxt.LineHist.Push(int(lexlineno), file)
+	Ctxt.LineHist.Push(int(lexlineno.Line()), file)
 }
 
 func linehistpop() {
 	if Debug['i'] != 0 {
 		fmt.Printf("end of import at line %v\n", linestr(lexlineno))
 	}
-	Ctxt.LineHist.Pop(int(lexlineno))
+	Ctxt.LineHist.Pop(int(lexlineno.Line()))
 }
 
 func linehistupdate(file string, off int) {
 	if Debug['i'] != 0 {
 		fmt.Printf("line %s at line %v\n", file, linestr(lexlineno))
 	}
-	Ctxt.LineHist.Update(int(lexlineno), file, off)
+	Ctxt.LineHist.Update(int(lexlineno.Line()), file, off)
 }
 
 func setlineno(n *Node) src.Pos {
@@ -216,9 +216,9 @@ func setlineno(n *Node) src.Pos {
 
 		default:
 			lineno = n.Lineno
-			if lineno == 0 {
+			if !lineno.IsKnown() {
 				if Debug['K'] != 0 {
-					Warn("setlineno: line 0")
+					Warn("setlineno: unknown position (line 0)")
 				}
 				lineno = lno
 			}
@@ -488,7 +488,7 @@ func treecopy(n *Node, lineno src.Pos) *Node {
 		m.Left = treecopy(n.Left, lineno)
 		m.Right = treecopy(n.Right, lineno)
 		m.List.Set(listtreecopy(n.List.Slice(), lineno))
-		if lineno != 0 {
+		if lineno.IsKnown() {
 			m.Lineno = lineno
 		}
 		if m.Name != nil && n.Op != ODCLFIELD {
@@ -504,7 +504,7 @@ func treecopy(n *Node, lineno src.Pos) *Node {
 			// so that all the copies of this const definition
 			// don't have the same iota value.
 			m := *n
-			if lineno != 0 {
+			if lineno.IsKnown() {
 				m.Lineno = lineno
 			}
 			m.SetIota(iota_)
@@ -1714,7 +1714,7 @@ func genwrapper(rcvr *Type, method *Field, newnam *Sym, iface int) {
 		fmt.Printf("genwrapper rcvrtype=%v method=%v newnam=%v\n", rcvr, method, newnam)
 	}
 
-	lexlineno++
+	lexlineno = src.MakePos(lexlineno.Line() + 1)
 	lineno = lexlineno
 	if genwrapper_linehistdone == 0 {
 		// All the wrappers can share the same linehist entry.
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 27bb6ed954..8da07c4ccd 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -3548,7 +3548,7 @@ func copytype(n *Node, t *Type) {
 	// Double-check use of type as embedded type.
 	lno := lineno
 
-	if embedlineno != 0 {
+	if embedlineno.IsKnown() {
 		lineno = embedlineno
 		if t.IsPtr() || t.IsUnsafePtr() {
 			yyerror("embedded type cannot be a pointer")
@@ -3629,7 +3629,7 @@ func typecheckdef(n *Node) *Node {
 	if n.Op == ONONAME {
 		if !n.Diag {
 			n.Diag = true
-			if n.Lineno != 0 {
+			if n.Lineno.IsKnown() {
 				lineno = n.Lineno
 			}
 
diff --git a/src/cmd/compile/internal/gc/util.go b/src/cmd/compile/internal/gc/util.go
index bb5cede5a6..adc8518bf4 100644
--- a/src/cmd/compile/internal/gc/util.go
+++ b/src/cmd/compile/internal/gc/util.go
@@ -11,7 +11,7 @@ import (
 )
 
 func (n *Node) Line() string {
-	return Ctxt.LineHist.LineString(int(n.Lineno))
+	return Ctxt.LineHist.LineString(int(n.Lineno.Line()))
 }
 
 var atExitFuncs []func()
diff --git a/src/cmd/compile/internal/mips/ssa.go b/src/cmd/compile/internal/mips/ssa.go
index aef1f90969..15ff16aa12 100644
--- a/src/cmd/compile/internal/mips/ssa.go
+++ b/src/cmd/compile/internal/mips/ssa.go
@@ -796,7 +796,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = mips.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpMIPSFPFlagTrue,
diff --git a/src/cmd/compile/internal/mips64/ssa.go b/src/cmd/compile/internal/mips64/ssa.go
index 1432c6ceea..d6c00d1a50 100644
--- a/src/cmd/compile/internal/mips64/ssa.go
+++ b/src/cmd/compile/internal/mips64/ssa.go
@@ -548,7 +548,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = mips.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpVarDef:
diff --git a/src/cmd/compile/internal/ppc64/ssa.go b/src/cmd/compile/internal/ppc64/ssa.go
index 8387692f86..3f36096565 100644
--- a/src/cmd/compile/internal/ppc64/ssa.go
+++ b/src/cmd/compile/internal/ppc64/ssa.go
@@ -803,7 +803,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = ppc64.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 
diff --git a/src/cmd/compile/internal/s390x/ssa.go b/src/cmd/compile/internal/s390x/ssa.go
index e2d3c2849b..61bf228d09 100644
--- a/src/cmd/compile/internal/s390x/ssa.go
+++ b/src/cmd/compile/internal/s390x/ssa.go
@@ -570,7 +570,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = s390x.REGTMP
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.OpS390XMVC:
diff --git a/src/cmd/compile/internal/ssa/compile.go b/src/cmd/compile/internal/ssa/compile.go
index b9ec7eb6b7..6fe731d1a3 100644
--- a/src/cmd/compile/internal/ssa/compile.go
+++ b/src/cmd/compile/internal/ssa/compile.go
@@ -5,6 +5,7 @@
 package ssa
 
 import (
+	"cmd/internal/src"
 	"fmt"
 	"log"
 	"os"
@@ -128,7 +129,7 @@ func (f *Func) dumpFile(phaseName string) {
 
 	fi, err := os.Create(fname)
 	if err != nil {
-		f.Config.Warnl(0, "Unable to create after-phase dump file %s", fname)
+		f.Config.Warnl(src.Pos{}, "Unable to create after-phase dump file %s", fname)
 		return
 	}
 
diff --git a/src/cmd/compile/internal/ssa/config.go b/src/cmd/compile/internal/ssa/config.go
index 031925e2fd..3cb9d9edb0 100644
--- a/src/cmd/compile/internal/ssa/config.go
+++ b/src/cmd/compile/internal/ssa/config.go
@@ -270,7 +270,7 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 		c.hasGReg = true
 		c.noDuffDevice = true
 	default:
-		fe.Fatalf(0, "arch %s not implemented", arch)
+		fe.Fatalf(src.Pos{}, "arch %s not implemented", arch)
 	}
 	c.ctxt = ctxt
 	c.optimize = optimize
@@ -310,7 +310,7 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 	if ev != "" {
 		v, err := strconv.ParseInt(ev, 10, 64)
 		if err != nil {
-			fe.Fatalf(0, "Environment variable GO_SSA_PHI_LOC_CUTOFF (value '%s') did not parse as a number", ev)
+			fe.Fatalf(src.Pos{}, "Environment variable GO_SSA_PHI_LOC_CUTOFF (value '%s') did not parse as a number", ev)
 		}
 		c.sparsePhiCutoff = uint64(v) // convert -1 to maxint, for never use sparse
 	}
@@ -332,7 +332,7 @@ func (c *Config) Ctxt() *obj.Link         { return c.ctxt }
 func (c *Config) NewFunc() *Func {
 	// TODO(khr): should this function take name, type, etc. as arguments?
 	if c.curFunc != nil {
-		c.Fatalf(0, "NewFunc called without previous Free")
+		c.Fatalf(src.Pos{}, "NewFunc called without previous Free")
 	}
 	f := &Func{Config: c, NamedValues: map[LocalSlot][]*Value{}}
 	c.curFunc = f
@@ -357,7 +357,7 @@ func (c *Config) logDebugHashMatch(evname, name string) {
 			var ok error
 			file, ok = os.Create(tmpfile)
 			if ok != nil {
-				c.Fatalf(0, "Could not open hash-testing logfile %s", tmpfile)
+				c.Fatalf(src.Pos{}, "Could not open hash-testing logfile %s", tmpfile)
 			}
 		}
 		c.logfiles[evname] = file
diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go
index 89ab17a427..0a4862be94 100644
--- a/src/cmd/compile/internal/ssa/deadstore.go
+++ b/src/cmd/compile/internal/ssa/deadstore.go
@@ -4,6 +4,8 @@
 
 package ssa
 
+import "cmd/internal/src"
+
 // dse does dead-store elimination on the Function.
 // Dead stores are those which are unconditionally followed by
 // another store to the same location, with no intervening load.
@@ -111,7 +113,7 @@ func dse(f *Func) {
 				if sz > 0x7fffffff { // work around sparseMap's int32 value type
 					sz = 0x7fffffff
 				}
-				shadowed.set(v.Args[0].ID, int32(sz), 0)
+				shadowed.set(v.Args[0].ID, int32(sz), src.Pos{})
 			}
 		}
 		// walk to previous store
diff --git a/src/cmd/compile/internal/ssa/func_test.go b/src/cmd/compile/internal/ssa/func_test.go
index 7136d8fb08..81f1c33cde 100644
--- a/src/cmd/compile/internal/ssa/func_test.go
+++ b/src/cmd/compile/internal/ssa/func_test.go
@@ -37,6 +37,7 @@ package ssa
 //                the parser can be used instead of Fun.
 
 import (
+	"cmd/internal/src"
 	"fmt"
 	"reflect"
 	"testing"
@@ -154,7 +155,7 @@ func Fun(c *Config, entry string, blocs ...bloc) fun {
 		blocks[bloc.name] = b
 		for _, valu := range bloc.valus {
 			// args are filled in the second pass.
-			values[valu.name] = b.NewValue0IA(0, valu.op, valu.t, valu.auxint, valu.aux)
+			values[valu.name] = b.NewValue0IA(src.Pos{}, valu.op, valu.t, valu.auxint, valu.aux)
 		}
 	}
 	// Connect the blocks together and specify control values.
@@ -428,12 +429,12 @@ func TestConstCache(t *testing.T) {
 		Bloc("entry",
 			Valu("mem", OpInitMem, TypeMem, 0, nil),
 			Exit("mem")))
-	v1 := f.f.ConstBool(0, TypeBool, false)
-	v2 := f.f.ConstBool(0, TypeBool, true)
+	v1 := f.f.ConstBool(src.Pos{}, TypeBool, false)
+	v2 := f.f.ConstBool(src.Pos{}, TypeBool, true)
 	f.f.freeValue(v1)
 	f.f.freeValue(v2)
-	v3 := f.f.ConstBool(0, TypeBool, false)
-	v4 := f.f.ConstBool(0, TypeBool, true)
+	v3 := f.f.ConstBool(src.Pos{}, TypeBool, false)
+	v4 := f.f.ConstBool(src.Pos{}, TypeBool, true)
 	if v3.AuxInt != 0 {
 		t.Errorf("expected %s to have auxint of 0\n", v3.LongString())
 	}
diff --git a/src/cmd/compile/internal/ssa/html.go b/src/cmd/compile/internal/ssa/html.go
index 316fd2aa25..355dc75e75 100644
--- a/src/cmd/compile/internal/ssa/html.go
+++ b/src/cmd/compile/internal/ssa/html.go
@@ -6,6 +6,7 @@ package ssa
 
 import (
 	"bytes"
+	"cmd/internal/src"
 	"fmt"
 	"html"
 	"io"
@@ -20,7 +21,7 @@ type HTMLWriter struct {
 func NewHTMLWriter(path string, logger Logger, funcname string) *HTMLWriter {
 	out, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
 	if err != nil {
-		logger.Fatalf(0, "%v", err)
+		logger.Fatalf(src.Pos{}, "%v", err)
 	}
 	html := HTMLWriter{File: out, Logger: logger}
 	html.start(funcname)
@@ -328,13 +329,13 @@ func (w *HTMLWriter) WriteColumn(title string, html string) {
 
 func (w *HTMLWriter) Printf(msg string, v ...interface{}) {
 	if _, err := fmt.Fprintf(w.File, msg, v...); err != nil {
-		w.Fatalf(0, "%v", err)
+		w.Fatalf(src.Pos{}, "%v", err)
 	}
 }
 
 func (w *HTMLWriter) WriteString(s string) {
 	if _, err := w.File.WriteString(s); err != nil {
-		w.Fatalf(0, "%v", err)
+		w.Fatalf(src.Pos{}, "%v", err)
 	}
 }
 
diff --git a/src/cmd/compile/internal/ssa/nilcheck.go b/src/cmd/compile/internal/ssa/nilcheck.go
index eb2d297f80..6345332ac1 100644
--- a/src/cmd/compile/internal/ssa/nilcheck.go
+++ b/src/cmd/compile/internal/ssa/nilcheck.go
@@ -101,7 +101,7 @@ func nilcheckelim(f *Func) {
 						// This is a redundant implicit nil check.
 						// Logging in the style of the former compiler -- and omit line 1,
 						// which is usually in generated code.
-						if f.Config.Debug_checknil() && v.Line > 1 {
+						if f.Config.Debug_checknil() && v.Line.Line() > 1 {
 							f.Config.Warnl(v.Line, "removed nil check")
 						}
 						v.reset(OpUnknown)
@@ -147,7 +147,7 @@ func nilcheckelim2(f *Func) {
 		for i := len(b.Values) - 1; i >= 0; i-- {
 			v := b.Values[i]
 			if opcodeTable[v.Op].nilCheck && unnecessary.contains(v.Args[0].ID) {
-				if f.Config.Debug_checknil() && int(v.Line) > 1 {
+				if f.Config.Debug_checknil() && v.Line.Line() > 1 {
 					f.Config.Warnl(v.Line, "removed nil check")
 				}
 				v.reset(OpUnknown)
diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index 9eecbdf57c..db68dda4d9 100644
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -555,7 +555,7 @@ func (s *regAllocState) init(f *Func) {
 		case "s390x":
 			// nothing to do, R10 & R11 already reserved
 		default:
-			s.f.Config.fe.Fatalf(0, "arch %s not implemented", s.f.Config.arch)
+			s.f.Config.fe.Fatalf(src.Pos{}, "arch %s not implemented", s.f.Config.arch)
 		}
 	}
 	if s.f.Config.nacl {
@@ -1912,13 +1912,13 @@ func (e *edgeState) setup(idx int, srcReg []endReg, dstReg []startReg, stacklive
 
 	// Live registers can be sources.
 	for _, x := range srcReg {
-		e.set(&e.s.registers[x.r], x.v.ID, x.c, false, 0) // don't care the line number of the source
+		e.set(&e.s.registers[x.r], x.v.ID, x.c, false, src.Pos{}) // don't care the line number of the source
 	}
 	// So can all of the spill locations.
 	for _, spillID := range stacklive {
 		v := e.s.orig[spillID]
 		spill := e.s.values[v.ID].spill
-		e.set(e.s.f.getHome(spillID), v.ID, spill, false, 0) // don't care the line number of the source
+		e.set(e.s.f.getHome(spillID), v.ID, spill, false, src.Pos{}) // don't care the line number of the source
 	}
 
 	// Figure out all the destinations we need.
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index 1a2eacccf8..0d582436ae 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -6526,7 +6526,7 @@ func rewriteValuegeneric_OpNilCheck(v *Value, config *Config) bool {
 		return true
 	}
 	// match: (NilCheck (Load (OffPtr [c] (SP)) mem) mem)
-	// cond: mem.Op == OpStaticCall 	&& isSameSym(mem.Aux, "runtime.newobject") 	&& c == config.ctxt.FixedFrameSize() + config.RegSize 	&& warnRule(config.Debug_checknil() && int(v.Line) > 1, v, "removed nil check")
+	// cond: mem.Op == OpStaticCall 	&& isSameSym(mem.Aux, "runtime.newobject") 	&& c == config.ctxt.FixedFrameSize() + config.RegSize 	&& warnRule(config.Debug_checknil() && v.Line.Line() > 1, v, "removed nil check")
 	// result: (Invalid)
 	for {
 		v_0 := v.Args[0]
@@ -6546,14 +6546,14 @@ func rewriteValuegeneric_OpNilCheck(v *Value, config *Config) bool {
 		if mem != v.Args[1] {
 			break
 		}
-		if !(mem.Op == OpStaticCall && isSameSym(mem.Aux, "runtime.newobject") && c == config.ctxt.FixedFrameSize()+config.RegSize && warnRule(config.Debug_checknil() && int(v.Line) > 1, v, "removed nil check")) {
+		if !(mem.Op == OpStaticCall && isSameSym(mem.Aux, "runtime.newobject") && c == config.ctxt.FixedFrameSize()+config.RegSize && warnRule(config.Debug_checknil() && v.Line.Line() > 1, v, "removed nil check")) {
 			break
 		}
 		v.reset(OpInvalid)
 		return true
 	}
 	// match: (NilCheck (OffPtr (Load (OffPtr [c] (SP)) mem)) mem)
-	// cond: mem.Op == OpStaticCall 	&& isSameSym(mem.Aux, "runtime.newobject") 	&& c == config.ctxt.FixedFrameSize() + config.RegSize 	&& warnRule(config.Debug_checknil() && int(v.Line) > 1, v, "removed nil check")
+	// cond: mem.Op == OpStaticCall 	&& isSameSym(mem.Aux, "runtime.newobject") 	&& c == config.ctxt.FixedFrameSize() + config.RegSize 	&& warnRule(config.Debug_checknil() && v.Line.Line() > 1, v, "removed nil check")
 	// result: (Invalid)
 	for {
 		v_0 := v.Args[0]
@@ -6577,7 +6577,7 @@ func rewriteValuegeneric_OpNilCheck(v *Value, config *Config) bool {
 		if mem != v.Args[1] {
 			break
 		}
-		if !(mem.Op == OpStaticCall && isSameSym(mem.Aux, "runtime.newobject") && c == config.ctxt.FixedFrameSize()+config.RegSize && warnRule(config.Debug_checknil() && int(v.Line) > 1, v, "removed nil check")) {
+		if !(mem.Op == OpStaticCall && isSameSym(mem.Aux, "runtime.newobject") && c == config.ctxt.FixedFrameSize()+config.RegSize && warnRule(config.Debug_checknil() && v.Line.Line() > 1, v, "removed nil check")) {
 			break
 		}
 		v.reset(OpInvalid)
diff --git a/src/cmd/compile/internal/ssa/schedule.go b/src/cmd/compile/internal/ssa/schedule.go
index f2a89d82d8..69c5cccd73 100644
--- a/src/cmd/compile/internal/ssa/schedule.go
+++ b/src/cmd/compile/internal/ssa/schedule.go
@@ -47,7 +47,7 @@ func (h ValHeap) Less(i, j int) bool {
 		return c > 0 // higher score comes later.
 	}
 	if x.Line != y.Line { // Favor in-order line stepping
-		return x.Line > y.Line
+		return x.Line.After(y.Line)
 	}
 	if x.Op != OpPhi {
 		if c := len(x.Args) - len(y.Args); c != 0 {
diff --git a/src/cmd/compile/internal/ssa/sparsemap.go b/src/cmd/compile/internal/ssa/sparsemap.go
index 3bc4eb9d78..d2a07e2534 100644
--- a/src/cmd/compile/internal/ssa/sparsemap.go
+++ b/src/cmd/compile/internal/ssa/sparsemap.go
@@ -66,7 +66,7 @@ func (s *sparseMap) setBit(k ID, v uint) {
 		s.dense[i].val |= 1 << v
 		return
 	}
-	s.dense = append(s.dense, sparseEntry{k, 1 << v, 0})
+	s.dense = append(s.dense, sparseEntry{k, 1 << v, src.Pos{}})
 	s.sparse[k] = int32(len(s.dense)) - 1
 }
 
diff --git a/src/cmd/compile/internal/ssa/stackalloc.go b/src/cmd/compile/internal/ssa/stackalloc.go
index dc2fd7d33b..599dc934f1 100644
--- a/src/cmd/compile/internal/ssa/stackalloc.go
+++ b/src/cmd/compile/internal/ssa/stackalloc.go
@@ -6,7 +6,10 @@
 
 package ssa
 
-import "fmt"
+import (
+	"cmd/internal/src"
+	"fmt"
+)
 
 type stackAllocState struct {
 	f *Func
@@ -37,7 +40,7 @@ func newStackAllocState(f *Func) *stackAllocState {
 		return new(stackAllocState)
 	}
 	if s.f != nil {
-		f.Config.Fatalf(0, "newStackAllocState called without previous free")
+		f.Config.Fatalf(src.Pos{}, "newStackAllocState called without previous free")
 	}
 	return s
 }
diff --git a/src/cmd/compile/internal/x86/ssa.go b/src/cmd/compile/internal/x86/ssa.go
index 21be63426a..52c3eebb20 100644
--- a/src/cmd/compile/internal/x86/ssa.go
+++ b/src/cmd/compile/internal/x86/ssa.go
@@ -788,7 +788,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.To.Type = obj.TYPE_MEM
 		p.To.Reg = v.Args[0].Reg()
 		gc.AddAux(&p.To, v)
-		if gc.Debug_checknil != 0 && v.Line > 1 { // v.Line==1 in generated wrappers
+		if gc.Debug_checknil != 0 && v.Line.Line() > 1 { // v.Line==1 in generated wrappers
 			gc.Warnl(v.Line, "generated nil check")
 		}
 	case ssa.Op386FCHS:
diff --git a/src/cmd/internal/src/src.go b/src/cmd/internal/src/src.go
index 2c3aef9efe..8691a9aa74 100644
--- a/src/cmd/internal/src/src.go
+++ b/src/cmd/internal/src/src.go
@@ -5,7 +5,25 @@
 // Package src implements source positions.
 package src
 
+// Implementation note: This is a thin abstraction over
+// the historic representation of source positions via
+// global line numbers. The abstraction will make it
+// easier to replace this implementation, eventually.
+
 // A Pos represents a source position.
-// It is an index into the global line table, which
-// maps a Pos to a file name and source line number.
-type Pos int32
+// The zero value for a Pos is a valid unknown position.
+type Pos struct {
+	// line is an index into the global line table, which maps
+	// the corresponding Pos to a file name and source line number.
+	line int32
+}
+
+// MakePos creates a new Pos from a line index.
+// It requires intimate knowledge of the underlying
+// implementation and should be used with caution.
+func MakePos(line int32) Pos { return Pos{line} }
+
+func (p Pos) IsKnown() bool     { return p.line != 0 }
+func (p Pos) Line() int32       { return p.line }
+func (p Pos) Before(q Pos) bool { return p.line < q.line }
+func (p Pos) After(q Pos) bool  { return p.line > q.line }