From: Keith Randall <khr@golang.org>
Date: Tue, 23 Feb 2016 07:19:00 +0000 (-0800)
Subject: [dev.ssa] cmd/compile: leave JMPs in when using -N
X-Git-Tag: go1.7beta1~1623^2^2~26
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=8906d2a171153ab337a88d4e9f59a7626ac55019;p=gostls13.git

[dev.ssa] cmd/compile: leave JMPs in when using -N

Helps keep line numbers around for debugging, particularly
for break and continue statements (which often compile
down to nothing).

Update #14379

Change-Id: I6ea06aa887b0450d9ba4f11e319e5c263f5a98ba
Reviewed-on: https://go-review.googlesource.com/19848
Reviewed-by: David Chase <drchase@google.com>
---

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 13d8663706..598f120155 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3627,7 +3627,10 @@ func genssa(f *ssa.Func, ptxt *obj.Prog, gcargs, gclocals *Sym) {
 		}
 		// Emit control flow instructions for block
 		var next *ssa.Block
-		if i < len(f.Blocks)-1 {
+		if i < len(f.Blocks)-1 && Debug['N'] == 0 {
+			// If -N, leave next==nil so every block with successors
+			// ends in a JMP.  Helps keep line numbers for otherwise
+			// empty blocks.
 			next = f.Blocks[i+1]
 		}
 		x := Pc
diff --git a/src/cmd/compile/internal/ssa/critical.go b/src/cmd/compile/internal/ssa/critical.go
index ba75450875..9fea0ec1cd 100644
--- a/src/cmd/compile/internal/ssa/critical.go
+++ b/src/cmd/compile/internal/ssa/critical.go
@@ -21,6 +21,7 @@ func critical(f *Func) {
 
 			// allocate a new block to place on the edge
 			d := f.NewBlock(BlockPlain)
+			d.Line = c.Line
 
 			// splice it in
 			d.Preds = append(d.Preds, c)