cmd/internal/obj: reimplement line history

In addition to possibly being clearer code,
this replaces an O(n) lookup with an O(log n) lookup.

Change-Id: I0a574c536a965a87f7ad6dcdcc30f737bc771cd5
Reviewed-on: https://go-review.googlesource.com/7623
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/gc/lex.go

@@ -1544,14 +1544,15 @@ func getlinepragma() int {
 			}
 			cp.WriteByte(byte(c))
 		}
-
 		cp = nil
 
-		if strings.HasPrefix(lexbuf.String(), "go:cgo_") {
-			pragcgo(lexbuf.String())
+		text := lexbuf.String()
+
+		if strings.HasPrefix(text, "go:cgo_") {
+			pragcgo(text)
 		}
 
-		cmd = lexbuf.String()
+		cmd = text
 		verb = cmd
 		if i := strings.Index(verb, " "); i >= 0 {
 			verb = verb[:i]
@@ -1630,8 +1631,9 @@ func getlinepragma() int {
 	if linep == 0 {
 		return c
 	}
+	text := lexbuf.String()
 	n := 0
-	for _, c := range lexbuf.String()[linep:] {
+	for _, c := range text[linep:] {
 		if c < '0' || c > '9' {
 			goto out
 		}
@@ -1646,15 +1648,7 @@ func getlinepragma() int {
 		return c
 	}
 
-	// try to avoid allocating file name over and over
-	name = lexbuf.String()[:linep-1]
-	for h := Ctxt.Hist; h != nil; h = h.Link {
-		if h.Name != "" && h.Name == name {
-			linehist(h.Name, int32(n), 0)
-			return c
-		}
-	}
-
+	name = text[:linep-1]
 	linehist(name, int32(n), 0)
 	return c
 

src/cmd/internal/obj/line_test.go

@@ -11,6 +11,7 @@ import (
 
 func TestLineHist(t *testing.T) {
 	ctxt := new(Link)
+	ctxt.Hash = make(map[SymVer]*LSym)
 
 	Linklinehist(ctxt, 1, "a.c", 0)
 	Linklinehist(ctxt, 3, "a.h", 0)
@@ -22,18 +23,18 @@ func TestLineHist(t *testing.T) {
 
 	var expect = []string{
 		0:  "??:0",
-		1:  "/a.c:1",
-		2:  "/a.c:2",
-		3:  "/a.h:1",
-		4:  "/a.h:2",
-		5:  "/a.c:3",
-		6:  "/a.c:4",
-		7:  "/linedir:2",
-		8:  "/linedir:3",
+		1:  "a.c:1",
+		2:  "a.c:2",
+		3:  "a.h:1",
+		4:  "a.h:2",
+		5:  "a.c:3",
+		6:  "a.c:4",
+		7:  "linedir:2",
+		8:  "linedir:3",
 		9:  "??:0",
 		10: "??:0",
-		11: "/b.c:1",
-		12: "/b.c:2",
+		11: "b.c:1",
+		12: "b.c:2",
 		13: "??:0",
 		14: "??:0",
 	}

src/cmd/internal/obj/link.go

@@ -183,8 +183,8 @@ type Link struct {
 	Hash               map[SymVer]*LSym
 	Allsym             *LSym
 	Nsymbol            int32
-	Hist               *Hist
-	Ehist              *Hist
+	LineHist           LineHist
+	Imports            []string
 	Plist              *Plist
 	Plast              *Plist
 	Sym_div            *LSym
@@ -580,3 +580,19 @@ const (
 )
 
 var linkbasepointer int
+
+/*
+ * start a new Prog list.
+ */
+func Linknewplist(ctxt *Link) *Plist {
+	pl := new(Plist)
+	*pl = Plist{}
+	if ctxt.Plist == nil {
+		ctxt.Plist = pl
+	} else {
+		ctxt.Plast.Link = pl
+	}
+	ctxt.Plast = pl
+
+	return pl
+}