From: Russ Cox <rsc@golang.org>
Date: Thu, 7 Oct 2010 08:42:26 +0000 (-0400)
Subject: gc: elide dead code
X-Git-Tag: weekly.2010-10-13~52
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=410927d1adeadbe8de72769bd794064f0cd801cd;p=gostls13.git

gc: elide dead code

R=ken2
CC=golang-dev
https://golang.org/cl/2365044
---

diff --git a/src/cmd/gc/gen.c b/src/cmd/gc/gen.c
index d2396aa09f..a8b2e1b8ed 100644
--- a/src/cmd/gc/gen.c
+++ b/src/cmd/gc/gen.c
@@ -257,6 +257,17 @@ gen(Node *n)
 		break;
 
 	case OIF:
+		if(n->ntest == N || n->ntest->op == OLITERAL) {
+			// drop dead code in if true or if false.
+			// the linker will do it for us in general,
+			// but this avoids writnig to the object file
+			// in a very common case.
+			if(n->ntest == N || n->ntest->val.u.bval)
+				genlist(n->nbody);
+			else
+				genlist(n->nelse);
+			break;
+		}
 		p1 = gjmp(P);			//		goto test
 		p2 = gjmp(P);			// p2:		goto else
 		patch(p1, pc);				// test: