From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Sat, 4 Jul 2015 16:07:54 +0000 (-0700)
Subject: [dev.ssa] cmd/compile/ssa: handle loops that don't loop
X-Git-Tag: go1.7beta1~1623^2^2~409
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=6c14059e65b180e3aaf34774b67ddffa461cf3c2;p=gostls13.git

[dev.ssa] cmd/compile/ssa: handle loops that don't loop

Loops such as

func f(c chan int) int {
	for x := range c {
		return x
	}
	return 0
}

don't loop. Remove the assumption that they must.

Partly fixes the build.

Change-Id: I766cebeec8e36d14512bea26f54c06c8eaf95e23
Reviewed-on: https://go-review.googlesource.com/11876
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index b21b4137dc..14c39d337f 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -409,8 +409,11 @@ func (s *state) stmt(n *Node) {
 			s.stmt(n.Right)
 		}
 		b = s.endBlock()
-		addEdge(b, bCond)
-
+		// If the body ends in a return statement,
+		// the condition check and loop are unreachable.
+		if b != nil {
+			addEdge(b, bCond)
+		}
 		s.startBlock(bEnd)
 
 	case OCALLFUNC: