1 files changed, 42 insertions, 10 deletions
diff --git a/src/cmd/compile/internal/ssa/print.go b/src/cmd/compile/internal/ssa/print.go
index d917183c70..96cd2c7c90 100644
--- a/src/cmd/compile/internal/ssa/print.go
+++ b/src/cmd/compile/internal/ssa/print.go
@@ -6,6 +6,7 @@ package ssa
 
 import (
 	"bytes"
+	"cmd/internal/src"
 	"crypto/sha256"
 	"fmt"
 	"io"
@@ -17,22 +18,30 @@ func printFunc(f *Func) {
 
 func hashFunc(f *Func) []byte {
 	h := sha256.New()
-	p := stringFuncPrinter{w: h}
+	p := stringFuncPrinter{w: h, printDead: true}
 	fprintFunc(p, f)
 	return h.Sum(nil)
 }
 
 func (f *Func) String() string {
 	var buf bytes.Buffer
-	p := stringFuncPrinter{w: &buf}
+	p := stringFuncPrinter{w: &buf, printDead: true}
 	fprintFunc(p, f)
 	return buf.String()
 }
 
+// rewriteHash returns a hash of f suitable for detecting rewrite cycles.
+func (f *Func) rewriteHash() string {
+	h := sha256.New()
+	p := stringFuncPrinter{w: h, printDead: false}
+	fprintFunc(p, f)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
 type funcPrinter interface {
 	header(f *Func)
 	startBlock(b *Block, reachable bool)
-	endBlock(b *Block)
+	endBlock(b *Block, reachable bool)
 	value(v *Value, live bool)
 	startDepCycle()
 	endDepCycle()
@@ -40,7 +49,8 @@ type funcPrinter interface {
 }
 
 type stringFuncPrinter struct {
-	w io.Writer
+	w         io.Writer
+	printDead bool
 }
 
 func (p stringFuncPrinter) header(f *Func) {
@@ -50,6 +60,9 @@ func (p stringFuncPrinter) header(f *Func) {
 }
 
 func (p stringFuncPrinter) startBlock(b *Block, reachable bool) {
+	if !p.printDead && !reachable {
+		return
+	}
 	fmt.Fprintf(p.w, "  b%d:", b.ID)
 	if len(b.Preds) > 0 {
 		io.WriteString(p.w, " <-")
@@ -64,14 +77,33 @@ func (p stringFuncPrinter) startBlock(b *Block, reachable bool) {
 	io.WriteString(p.w, "\n")
 }
 
-func (p stringFuncPrinter) endBlock(b *Block) {
+func (p stringFuncPrinter) endBlock(b *Block, reachable bool) {
+	if !p.printDead && !reachable {
+		return
+	}
 	fmt.Fprintln(p.w, "    "+b.LongString())
 }
 
+func StmtString(p src.XPos) string {
+	linenumber := "(?) "
+	if p.IsKnown() {
+		pfx := ""
+		if p.IsStmt() == src.PosIsStmt {
+			pfx = "+"
+		}
+		if p.IsStmt() == src.PosNotStmt {
+			pfx = "-"
+		}
+		linenumber = fmt.Sprintf("(%s%d) ", pfx, p.Line())
+	}
+	return linenumber
+}
+
 func (p stringFuncPrinter) value(v *Value, live bool) {
-	fmt.Fprint(p.w, "    ")
-	//fmt.Fprint(p.w, v.Block.Func.fe.Pos(v.Pos))
-	//fmt.Fprint(p.w, ": ")
+	if !p.printDead && !live {
+		return
+	}
+	fmt.Fprintf(p.w, "    %s", StmtString(v.Pos))
 	fmt.Fprint(p.w, v.LongString())
 	if !live {
 		fmt.Fprint(p.w, " DEAD")
@@ -103,7 +135,7 @@ func fprintFunc(p funcPrinter, f *Func) {
 				p.value(v, live[v.ID])
 				printed[v.ID] = true
 			}
-			p.endBlock(b)
+			p.endBlock(b, reachable[b.ID])
 			continue
 		}
 
@@ -151,7 +183,7 @@ func fprintFunc(p funcPrinter, f *Func) {
 			}
 		}
 
-		p.endBlock(b)
+		p.endBlock(b, reachable[b.ID])
 	}
 	for _, name := range f.Names {
 		p.named(*name, f.NamedValues[*name])