[dev.ssa] cmd/compile: add HTML SSA printer

This is an initial implementation.
There are many rough edges and TODOs,
which will hopefully be polished out
with use.

Fixes #12071.

Change-Id: I1d6fd5a343063b5200623bceef2c2cfcc885794e
Reviewed-on: https://go-review.googlesource.com/13472
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -5,7 +5,9 @@
 package gc
 
 import (
+	"bytes"
 	"fmt"
+	"html"
 	"os"
 	"strings"
 
@@ -40,6 +42,18 @@ func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 	s.f = s.config.NewFunc()
 	s.f.Name = name
 
+	if name == os.Getenv("GOSSAFUNC") {
+		// TODO: tempfile? it is handy to have the location
+		// of this file be stable, so you can just reload in the browser.
+		s.config.HTML = ssa.NewHTMLWriter("ssa.html", &s, name)
+		// TODO: generate and print a mapping from nodes to values and blocks
+	}
+	defer func() {
+		if !usessa {
+			s.config.HTML.Close()
+		}
+	}()
+
 	// If SSA support for the function is incomplete,
 	// assume that any panics are due to violated
 	// invariants. Swallow them silently.
@@ -1811,6 +1825,30 @@ func genssa(f *ssa.Func, ptxt *obj.Prog, gcargs, gclocals *Sym) {
 			}
 			f.Logf("%s\t%s\n", s, p)
 		}
+		if f.Config.HTML != nil {
+			saved := ptxt.Ctxt.LineHist.PrintFilenameOnly
+			ptxt.Ctxt.LineHist.PrintFilenameOnly = true
+			var buf bytes.Buffer
+			buf.WriteString("<code>")
+			buf.WriteString("<dl class=\"ssa-gen\">")
+			for p := ptxt; p != nil; p = p.Link {
+				buf.WriteString("<dt class=\"ssa-prog-src\">")
+				if v, ok := valueProgs[p]; ok {
+					buf.WriteString(v.HTML())
+				} else if b, ok := blockProgs[p]; ok {
+					buf.WriteString(b.HTML())
+				}
+				buf.WriteString("</dt>")
+				buf.WriteString("<dd class=\"ssa-prog\">")
+				buf.WriteString(html.EscapeString(p.String()))
+				buf.WriteString("</dd>")
+				buf.WriteString("</li>")
+			}
+			buf.WriteString("</dl>")
+			buf.WriteString("</code>")
+			f.Config.HTML.WriteColumn("genssa", buf.String())
+			ptxt.Ctxt.LineHist.PrintFilenameOnly = saved
+		}
 	}
 
 	// Emit static data
@@ -1834,6 +1872,8 @@ func genssa(f *ssa.Func, ptxt *obj.Prog, gcargs, gclocals *Sym) {
 	ggloblsym(gcargs, 4, obj.RODATA|obj.DUPOK)
 	duint32(gclocals, 0, 0)
 	ggloblsym(gclocals, 4, obj.RODATA|obj.DUPOK)
+
+	f.Config.HTML.Close()
 }
 
 func genValue(v *ssa.Value) {

src/cmd/compile/internal/ssa/compile.go

@@ -34,13 +34,16 @@ func Compile(f *Func) {
 
 	// Run all the passes
 	printFunc(f)
+	f.Config.HTML.WriteFunc("start", f)
 	checkFunc(f)
 	for _, p := range passes {
 		phaseName = p.name
 		f.Logf("  pass %s begin\n", p.name)
+		// TODO: capture logging during this pass, add it to the HTML
 		p.fn(f)
 		f.Logf("  pass %s end\n", p.name)
 		printFunc(f)
+		f.Config.HTML.WriteFunc("after "+phaseName, f)
 		checkFunc(f)
 	}
 

src/cmd/compile/internal/ssa/config.go

@@ -11,6 +11,7 @@ type Config struct {
 	lowerBlock func(*Block) bool          // lowering function
 	lowerValue func(*Value, *Config) bool // lowering function
 	fe         Frontend                   // callbacks into compiler frontend
+	HTML       *HTMLWriter                // html writer, for debugging
 
 	// TODO: more stuff.  Compiler flags of interest, ...
 }
@@ -31,12 +32,7 @@ type TypeSource interface {
 	TypeBytePtr() Type // TODO: use unsafe.Pointer instead?
 }
 
-type Frontend interface {
-	TypeSource
-
-	// StringData returns a symbol pointing to the given string's contents.
-	StringData(string) interface{} // returns *gc.Sym
-
+type Logger interface {
 	// Log logs a message from the compiler.
 	Logf(string, ...interface{})
 
@@ -48,6 +44,14 @@ type Frontend interface {
 	Unimplementedf(msg string, args ...interface{})
 }
 
+type Frontend interface {
+	TypeSource
+	Logger
+
+	// StringData returns a symbol pointing to the given string's contents.
+	StringData(string) interface{} // returns *gc.Sym
+}
+
 // NewConfig returns a new configuration object for the given architecture.
 func NewConfig(arch string, fe Frontend) *Config {
 	c := &Config{arch: arch, fe: fe}

src/cmd/compile/internal/ssa/deadcode.go

@@ -4,10 +4,10 @@
 
 package ssa
 
-// deadcode removes dead code from f.
-func deadcode(f *Func) {
+// findlive returns the reachable blocks and live values in f.
+func findlive(f *Func) (reachable []bool, live []bool) {
 	// Find all reachable basic blocks.
-	reachable := make([]bool, f.NumBlocks())
+	reachable = make([]bool, f.NumBlocks())
 	reachable[f.Entry.ID] = true
 	p := []*Block{f.Entry} // stack-like worklist
 	for len(p) > 0 {
@@ -24,8 +24,8 @@ func deadcode(f *Func) {
 	}
 
 	// Find all live values
-	live := make([]bool, f.NumValues()) // flag to set for each live value
-	var q []*Value                      // stack-like worklist of unscanned values
+	live = make([]bool, f.NumValues()) // flag to set for each live value
+	var q []*Value                     // stack-like worklist of unscanned values
 
 	// Starting set: all control values of reachable blocks are live.
 	for _, b := range f.Blocks {
@@ -54,6 +54,13 @@ func deadcode(f *Func) {
 		}
 	}
 
+	return reachable, live
+}
+
+// deadcode removes dead code from f.
+func deadcode(f *Func) {
+	reachable, live := findlive(f)
+
 	// Remove dead values from blocks' value list.  Return dead
 	// value ids to the allocator.
 	for _, b := range f.Blocks {

src/cmd/compile/internal/ssa/html.go

@@ -0,0 +1,461 @@
+// 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.
+
+package ssa
+
+import (
+	"bytes"
+	"fmt"
+	"html"
+	"io"
+	"os"
+)
+
+type HTMLWriter struct {
+	Logger
+	*os.File
+}
+
+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("%v", err)
+	}
+	html := HTMLWriter{File: out, Logger: logger}
+	html.start(funcname)
+	return &html
+}
+
+func (w *HTMLWriter) start(name string) {
+	if w == nil {
+		return
+	}
+	w.WriteString("<html>")
+	w.WriteString(`<head>
+<style>
+
+#helplink {
+    margin-bottom: 15px;
+    display: block;
+    margin-top: -15px;
+}
+
+#help {
+    display: none;
+}
+
+table {
+    border: 1px solid black;
+    table-layout: fixed;
+    width: 300px;
+}
+
+th, td {
+    border: 1px solid black;
+    overflow: hidden;
+    width: 400px;
+    vertical-align: top;
+    padding: 5px;
+}
+
+li {
+    list-style-type: none;
+}
+
+li.ssa-long-value {
+    text-indent: -2em;  /* indent wrapped lines */
+}
+
+li.ssa-value-list {
+    display: inline;
+}
+
+li.ssa-start-block {
+    padding: 0;
+    margin: 0;
+}
+
+li.ssa-end-block {
+    padding: 0;
+    margin: 0;
+}
+
+ul.ssa-print-func {
+    padding-left: 0;
+}
+
+dl.ssa-gen {
+    padding-left: 0;
+}
+
+dt.ssa-prog-src {
+    padding: 0;
+    margin: 0;
+    float: left;
+    width: 4em;
+}
+
+dd.ssa-prog {
+    padding: 0;
+    margin-right: 0;
+    margin-left: 4em;
+}
+
+.dead-value {
+    color: gray;
+}
+
+.dead-block {
+    opacity: 0.5;
+}
+
+.depcycle {
+    font-style: italic;
+}
+
+.highlight-yellow         { background-color: yellow; }
+.highlight-aquamarine     { background-color: aquamarine; }
+.highlight-coral          { background-color: coral; }
+.highlight-lightpink      { background-color: lightpink; }
+.highlight-lightsteelblue { background-color: lightsteelblue; }
+.highlight-palegreen      { background-color: palegreen; }
+.highlight-powderblue     { background-color: powderblue; }
+.highlight-lightgray      { background-color: lightgray; }
+
+.outline-blue           { outline: blue solid 2px; }
+.outline-red            { outline: red solid 2px; }
+.outline-blueviolet     { outline: blueviolet solid 2px; }
+.outline-darkolivegreen { outline: darkolivegreen solid 2px; }
+.outline-fuchsia        { outline: fuchsia solid 2px; }
+.outline-sienna         { outline: sienna solid 2px; }
+.outline-gold           { outline: gold solid 2px; }
+
+</style>
+
+<script type="text/javascript">
+// ordered list of all available highlight colors
+var highlights = [
+    "highlight-yellow",
+    "highlight-aquamarine",
+    "highlight-coral",
+    "highlight-lightpink",
+    "highlight-lightsteelblue",
+    "highlight-palegreen",
+    "highlight-lightgray"
+];
+
+// state: which value is highlighted this color?
+var highlighted = {};
+for (var i = 0; i < highlights.length; i++) {
+    highlighted[highlights[i]] = "";
+}
+
+// ordered list of all available outline colors
+var outlines = [
+    "outline-blue",
+    "outline-red",
+    "outline-blueviolet",
+    "outline-darkolivegreen",
+    "outline-fuchsia",
+    "outline-sienna",
+    "outline-gold"
+];
+
+// state: which value is outlined this color?
+var outlined = {};
+for (var i = 0; i < outlines.length; i++) {
+    outlined[outlines[i]] = "";
+}
+
+window.onload = function() {
+    var ssaElemClicked = function(elem, event, selections, selected) {
+        event.stopPropagation()
+
+        // TODO: pushState with updated state and read it on page load,
+        // so that state can survive across reloads
+
+        // find all values with the same name
+        var c = elem.classList.item(0);
+        var x = document.getElementsByClassName(c);
+
+        // if selected, remove selections from all of them
+        // otherwise, attempt to add
+
+        var remove = "";
+        for (var i = 0; i < selections.length; i++) {
+            var color = selections[i];
+            if (selected[color] == c) {
+                remove = color;
+                break;
+            }
+        }
+
+        if (remove != "") {
+            for (var i = 0; i < x.length; i++) {
+                x[i].classList.remove(remove);
+            }
+            selected[remove] = "";
+            return;
+        }
+
+        // we're adding a selection
+        // find first available color
+        var avail = "";
+        for (var i = 0; i < selections.length; i++) {
+            var color = selections[i];
+            if (selected[color] == "") {
+                avail = color;
+                break;
+            }
+        }
+        if (avail == "") {
+            alert("out of selection colors; go add more");
+            return;
+        }
+
+        // set that as the selection
+        for (var i = 0; i < x.length; i++) {
+            x[i].classList.add(avail);
+        }
+        selected[avail] = c;
+    };
+
+    var ssaValueClicked = function(event) {
+        ssaElemClicked(this, event, highlights, highlighted);
+    }
+
+    var ssaBlockClicked = function(event) {
+        ssaElemClicked(this, event, outlines, outlined);
+    }
+
+    var ssavalues = document.getElementsByClassName("ssa-value");
+    for (var i = 0; i < ssavalues.length; i++) {
+        ssavalues[i].addEventListener('click', ssaValueClicked);
+    }
+
+    var ssalongvalues = document.getElementsByClassName("ssa-long-value");
+    for (var i = 0; i < ssalongvalues.length; i++) {
+        // don't attach listeners to li nodes, just the spans they contain
+        if (ssalongvalues[i].nodeName == "SPAN") {
+            ssalongvalues[i].addEventListener('click', ssaValueClicked);
+        }
+    }
+
+    var ssablocks = document.getElementsByClassName("ssa-block");
+    for (var i = 0; i < ssablocks.length; i++) {
+        ssablocks[i].addEventListener('click', ssaBlockClicked);
+    }
+};
+
+function toggle_visibility(id) {
+   var e = document.getElementById(id);
+   if(e.style.display == 'block')
+      e.style.display = 'none';
+   else
+      e.style.display = 'block';
+}
+</script>
+
+</head>`)
+	// TODO: Add javascript click handlers for blocks
+	// to outline that block across all phases
+	w.WriteString("<body>")
+	w.WriteString("<h1>")
+	w.WriteString(html.EscapeString(name))
+	w.WriteString("</h1>")
+	w.WriteString(`
+<a href="#" onclick="toggle_visibility('help');" id="helplink">help</a>
+<div id="help">
+
+<p>
+Click on a value or block to toggle highlighting of that value/block and its uses.
+Values and blocks are highlighted by ID, which may vary across passes.
+(TODO: Fix this.)
+</p>
+
+<p>
+Faded out values and blocks are dead code that has not been eliminated.
+</p>
+
+<p>
+Values printed in italics have a dependency cycle.
+</p>
+
+</div>
+`)
+	w.WriteString("<table>")
+	w.WriteString("<tr>")
+}
+
+func (w *HTMLWriter) Close() {
+	if w == nil {
+		return
+	}
+	w.WriteString("</tr>")
+	w.WriteString("</table>")
+	w.WriteString("</body>")
+	w.WriteString("</html>")
+	w.File.Close()
+}
+
+// WriteFunc writes f in a column headed by title.
+func (w *HTMLWriter) WriteFunc(title string, f *Func) {
+	if w == nil {
+		return // avoid generating HTML just to discard it
+	}
+	w.WriteColumn(title, f.HTML())
+	// TODO: Add visual representation of f's CFG.
+}
+
+// WriteColumn writes raw HTML in a column headed by title.
+// It is intended for pre- and post-compilation log output.
+func (w *HTMLWriter) WriteColumn(title string, html string) {
+	if w == nil {
+		return
+	}
+	w.WriteString("<td>")
+	w.WriteString("<h2>" + title + "</h2>")
+	w.WriteString(html)
+	w.WriteString("</td>")
+}
+
+func (w *HTMLWriter) Printf(msg string, v ...interface{}) {
+	if _, err := fmt.Fprintf(w.File, msg, v...); err != nil {
+		w.Fatalf("%v", err)
+	}
+}
+
+func (w *HTMLWriter) WriteString(s string) {
+	if _, err := w.File.WriteString(s); err != nil {
+		w.Fatalf("%v", err)
+	}
+}
+
+func (v *Value) HTML() string {
+	// TODO: Using the value ID as the class ignores the fact
+	// that value IDs get recycled and that some values
+	// are transmuted into other values.
+	return fmt.Sprintf("<span class=\"%[1]s ssa-value\">%[1]s</span>", v.String())
+}
+
+func (v *Value) LongHTML() string {
+	// TODO: Any intra-value formatting?
+	// I'm wary of adding too much visual noise,
+	// but a little bit might be valuable.
+	// We already have visual noise in the form of punctuation
+	// maybe we could replace some of that with formatting.
+	s := fmt.Sprintf("<span class=\"%s ssa-long-value\">", v.String())
+	s += fmt.Sprintf("%s = %s", v.HTML(), v.Op.String())
+	s += " &lt;" + html.EscapeString(v.Type.String()) + "&gt;"
+	if v.AuxInt != 0 {
+		s += fmt.Sprintf(" [%d]", v.AuxInt)
+	}
+	if v.Aux != nil {
+		if _, ok := v.Aux.(string); ok {
+			s += html.EscapeString(fmt.Sprintf(" {%q}", v.Aux))
+		} else {
+			s += html.EscapeString(fmt.Sprintf(" {%v}", v.Aux))
+		}
+	}
+	for _, a := range v.Args {
+		s += fmt.Sprintf(" %s", a.HTML())
+	}
+	r := v.Block.Func.RegAlloc
+	if r != nil && r[v.ID] != nil {
+		s += " : " + r[v.ID].Name()
+	}
+
+	s += "</span>"
+	return s
+}
+
+func (b *Block) HTML() string {
+	// TODO: Using the value ID as the class ignores the fact
+	// that value IDs get recycled and that some values
+	// are transmuted into other values.
+	return fmt.Sprintf("<span class=\"%[1]s ssa-block\">%[1]s</span>", html.EscapeString(b.String()))
+}
+
+func (b *Block) LongHTML() string {
+	// TODO: improve this for HTML?
+	s := b.Kind.String()
+	if b.Control != nil {
+		s += fmt.Sprintf(" %s", b.Control.HTML())
+	}
+	if len(b.Succs) > 0 {
+		s += " &#8594;" // right arrow
+		for _, c := range b.Succs {
+			s += " " + c.HTML()
+		}
+	}
+	return s
+}
+
+func (f *Func) HTML() string {
+	var buf bytes.Buffer
+	fmt.Fprint(&buf, "<code>")
+	p := htmlFuncPrinter{w: &buf}
+	fprintFunc(p, f)
+
+	// fprintFunc(&buf, f) // TODO: HTML, not text, <br /> for line breaks, etc.
+	fmt.Fprint(&buf, "</code>")
+	return buf.String()
+}
+
+type htmlFuncPrinter struct {
+	w io.Writer
+}
+
+func (p htmlFuncPrinter) header(f *Func) {}
+
+func (p htmlFuncPrinter) startBlock(b *Block, reachable bool) {
+	// TODO: Make blocks collapsable?
+	var dead string
+	if !reachable {
+		dead = "dead-block"
+	}
+	fmt.Fprintf(p.w, "<ul class=\"%s ssa-print-func %s\">", b, dead)
+	fmt.Fprintf(p.w, "<li class=\"ssa-start-block\">%s:", b.HTML())
+	if len(b.Preds) > 0 {
+		io.WriteString(p.w, " &#8592;") // left arrow
+		for _, pred := range b.Preds {
+			fmt.Fprintf(p.w, " %s", pred.HTML())
+		}
+	}
+	io.WriteString(p.w, "</li>")
+	if len(b.Values) > 0 { // start list of values
+		io.WriteString(p.w, "<li class=\"ssa-value-list\">")
+		io.WriteString(p.w, "<ul>")
+	}
+}
+
+func (p htmlFuncPrinter) endBlock(b *Block) {
+	if len(b.Values) > 0 { // end list of values
+		io.WriteString(p.w, "</ul>")
+		io.WriteString(p.w, "</li>")
+	}
+	io.WriteString(p.w, "<li class=\"ssa-end-block\">")
+	fmt.Fprint(p.w, b.LongHTML())
+	io.WriteString(p.w, "</li>")
+	io.WriteString(p.w, "</ul>")
+	// io.WriteString(p.w, "</span>")
+}
+
+func (p htmlFuncPrinter) value(v *Value, live bool) {
+	var dead string
+	if !live {
+		dead = "dead-value"
+	}
+	fmt.Fprintf(p.w, "<li class=\"ssa-long-value %s\">", dead)
+	fmt.Fprint(p.w, v.LongHTML())
+	io.WriteString(p.w, "</li>")
+}
+
+func (p htmlFuncPrinter) startDepCycle() {
+	fmt.Fprintln(p.w, "<span class=\"depcycle\">")
+}
+
+func (p htmlFuncPrinter) endDepCycle() {
+	fmt.Fprintln(p.w, "</span>")
+}

src/cmd/compile/internal/ssa/print.go

@@ -16,33 +16,77 @@ func printFunc(f *Func) {
 
 func (f *Func) String() string {
 	var buf bytes.Buffer
-	fprintFunc(&buf, f)
+	p := stringFuncPrinter{w: &buf}
+	fprintFunc(p, f)
 	return buf.String()
 }
 
-func fprintFunc(w io.Writer, f *Func) {
-	fmt.Fprint(w, f.Name)
-	fmt.Fprint(w, " ")
-	fmt.Fprintln(w, f.Type)
+type funcPrinter interface {
+	header(f *Func)
+	startBlock(b *Block, reachable bool)
+	endBlock(b *Block)
+	value(v *Value, live bool)
+	startDepCycle()
+	endDepCycle()
+}
+
+type stringFuncPrinter struct {
+	w io.Writer
+}
+
+func (p stringFuncPrinter) header(f *Func) {
+	fmt.Fprint(p.w, f.Name)
+	fmt.Fprint(p.w, " ")
+	fmt.Fprintln(p.w, f.Type)
+}
+
+func (p stringFuncPrinter) startBlock(b *Block, reachable bool) {
+	fmt.Fprintf(p.w, "  b%d:", b.ID)
+	if len(b.Preds) > 0 {
+		io.WriteString(p.w, " <-")
+		for _, pred := range b.Preds {
+			fmt.Fprintf(p.w, " b%d", pred.ID)
+		}
+	}
+	if !reachable {
+		fmt.Fprint(p.w, " DEAD")
+	}
+	io.WriteString(p.w, "\n")
+}
+
+func (p stringFuncPrinter) endBlock(b *Block) {
+	fmt.Fprintln(p.w, "    "+b.LongString())
+}
+
+func (p stringFuncPrinter) value(v *Value, live bool) {
+	fmt.Fprint(p.w, "    ")
+	fmt.Fprint(p.w, v.LongString())
+	if !live {
+		fmt.Fprint(p.w, " DEAD")
+	}
+	fmt.Fprintln(p.w)
+}
+
+func (p stringFuncPrinter) startDepCycle() {
+	fmt.Fprintln(p.w, "dependency cycle!")
+}
+
+func (p stringFuncPrinter) endDepCycle() {}
+
+func fprintFunc(p funcPrinter, f *Func) {
+	reachable, live := findlive(f)
+	p.header(f)
 	printed := make([]bool, f.NumValues())
 	for _, b := range f.Blocks {
-		fmt.Fprintf(w, "  b%d:", b.ID)
-		if len(b.Preds) > 0 {
-			io.WriteString(w, " <-")
-			for _, pred := range b.Preds {
-				fmt.Fprintf(w, " b%d", pred.ID)
-			}
-		}
-		io.WriteString(w, "\n")
+		p.startBlock(b, reachable[b.ID])
 
 		if f.scheduled {
 			// Order of Values has been decided - print in that order.
 			for _, v := range b.Values {
-				fmt.Fprint(w, "    ")
-				fmt.Fprintln(w, v.LongString())
+				p.value(v, live[v.ID])
 				printed[v.ID] = true
 			}
-			fmt.Fprintln(w, "    "+b.LongString())
+			p.endBlock(b)
 			continue
 		}
 
@@ -52,8 +96,7 @@ func fprintFunc(w io.Writer, f *Func) {
 			if v.Op != OpPhi {
 				continue
 			}
-			fmt.Fprint(w, "    ")
-			fmt.Fprintln(w, v.LongString())
+			p.value(v, live[v.ID])
 			printed[v.ID] = true
 			n++
 		}
@@ -73,25 +116,24 @@ func fprintFunc(w io.Writer, f *Func) {
 						continue outer
 					}
 				}
-				fmt.Fprint(w, "    ")
-				fmt.Fprintln(w, v.LongString())
+				p.value(v, live[v.ID])
 				printed[v.ID] = true
 				n++
 			}
 			if m == n {
-				fmt.Fprintln(w, "dependency cycle!")
+				p.startDepCycle()
 				for _, v := range b.Values {
 					if printed[v.ID] {
 						continue
 					}
-					fmt.Fprint(w, "    ")
-					fmt.Fprintln(w, v.LongString())
+					p.value(v, live[v.ID])
 					printed[v.ID] = true
 					n++
 				}
+				p.endDepCycle()
 			}
 		}
 
-		fmt.Fprintln(w, "    "+b.LongString())
+		p.endBlock(b)
 	}
 }

src/cmd/internal/obj/obj.go

@@ -25,12 +25,13 @@ import (
 //	  together, so that given (only) calls Push(10, "x.go", 1) and Pop(15),
 //	  virtual line 12 corresponds to x.go line 3.
 type LineHist struct {
-	Top            *LineStack  // current top of stack
-	Ranges         []LineRange // ranges for lookup
-	Dir            string      // directory to qualify relative paths
-	TrimPathPrefix string      // remove leading TrimPath from recorded file names
-	GOROOT         string      // current GOROOT
-	GOROOT_FINAL   string      // target GOROOT
+	Top               *LineStack  // current top of stack
+	Ranges            []LineRange // ranges for lookup
+	Dir               string      // directory to qualify relative paths
+	TrimPathPrefix    string      // remove leading TrimPath from recorded file names
+	PrintFilenameOnly bool        // ignore path when pretty-printing a line; internal use only
+	GOROOT            string      // current GOROOT
+	GOROOT_FINAL      string      // target GOROOT
 }
 
 // A LineStack is an entry in the recorded line history.
@@ -221,20 +222,24 @@ func (h *LineHist) LineString(lineno int) string {
 		return "<unknown line number>"
 	}
 
-	text := fmt.Sprintf("%s:%d", stk.File, stk.fileLineAt(lineno))
+	filename := stk.File
+	if h.PrintFilenameOnly {
+		filename = filepath.Base(filename)
+	}
+	text := fmt.Sprintf("%s:%d", filename, stk.fileLineAt(lineno))
 	if stk.Directive && stk.Parent != nil {
 		stk = stk.Parent
-		text += fmt.Sprintf("[%s:%d]", stk.File, stk.fileLineAt(lineno))
+		text += fmt.Sprintf("[%s:%d]", filename, stk.fileLineAt(lineno))
 	}
 	const showFullStack = false // was used by old C compilers
 	if showFullStack {
 		for stk.Parent != nil {
 			lineno = stk.Lineno - 1
 			stk = stk.Parent
-			text += fmt.Sprintf(" %s:%d", stk.File, stk.fileLineAt(lineno))
+			text += fmt.Sprintf(" %s:%d", filename, stk.fileLineAt(lineno))
 			if stk.Directive && stk.Parent != nil {
 				stk = stk.Parent
-				text += fmt.Sprintf("[%s:%d]", stk.File, stk.fileLineAt(lineno))
+				text += fmt.Sprintf("[%s:%d]", filename, stk.fileLineAt(lineno))
 			}
 		}
 	}