[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/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)
 	}
 }