From: Dave Cheney <dave@cheney.net>
Date: Sun, 4 Nov 2012 09:06:37 +0000 (+1100)
Subject: cmd/5g: improve shift code generation
X-Git-Tag: go1.1rc2~1965
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=d8008a9eef07e235358f0f7ca94a729aad4aa3b1;p=gostls13.git

cmd/5g: improve shift code generation

This CL is a backport of 6012049 which improves code
generation for shift operations.

benchmark       old ns/op    new ns/op    delta
BenchmarkLSL            9            5  -49.67%
BenchmarkLSR            9            4  -50.00%

R=golang-dev, minux.ma, r, rsc
CC=golang-dev
https://golang.org/cl/6813045
---

diff --git a/src/cmd/5g/ggen.c b/src/cmd/5g/ggen.c
index a60f414943..8566f935df 100644
--- a/src/cmd/5g/ggen.c
+++ b/src/cmd/5g/ggen.c
@@ -407,7 +407,9 @@ cgen_asop(Node *n)
 hard:
 	n2.op = 0;
 	n1.op = 0;
-	if(nr->ullman >= nl->ullman || nl->addable) {
+	if(nr->op == OLITERAL) {
+		// don't allocate a register for literals.
+	} else if(nr->ullman >= nl->ullman || nl->addable) {
 		regalloc(&n2, nr->type, N);
 		cgen(nr, &n2);
 		nr = &n2;