From: Rui Ueyama <ruiu@google.com>
Date: Wed, 6 Aug 2014 04:10:07 +0000 (-0700)
Subject: liblink: shorter encoding for zeroing register
X-Git-Tag: go1.4beta1~939
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=24db88168997d650e8274dd2e84e8a56bf8d95b9;p=gostls13.git

liblink: shorter encoding for zeroing register

Encode MOV $0, %ax as XOR %eax, %eax instead of
XOR %rax, %rax. If an operand register does not
need REX.w bit (i.e. not one of R8-R15), it is
encoded in 2 bytes instead of 3 bytes.

LGTM=rsc
R=golang-codereviews, gobot, rsc
CC=golang-codereviews
https://golang.org/cl/115580044
---

diff --git a/src/liblink/asm6.c b/src/liblink/asm6.c
index 454b30239a..3fc3e01286 100644
--- a/src/liblink/asm6.c
+++ b/src/liblink/asm6.c
@@ -3066,6 +3066,7 @@ found:
 		break;
 
 	case Zclr:
+		ctxt->rexflag &= ~Pw;
 		*ctxt->andptr++ = op;
 		asmand(ctxt, &p->to, &p->to);
 		break;