From: Jake Ciolek <jakub@ciolek.dev>
Date: Sat, 9 Oct 2021 18:09:21 +0000 (+0200)
Subject: cmd/compile: use the shorter version of XOR for breaking POPCNT register
X-Git-Tag: go1.18beta1~960
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=b99abf3cce16721d79351c92031239a27fec3d22;p=gostls13.git

cmd/compile: use the shorter version of XOR for breaking POPCNT register

dependency

XORL accomplishes the same thing while being shorter to encode.

Change-Id: I4397999ff617edb61a7fb7d1eca757a202ab8134
Reviewed-on: https://go-review.googlesource.com/c/go/+/354832
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
---

diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go
index 33cd5985e0..78822098a7 100644
--- a/src/cmd/compile/internal/amd64/ssa.go
+++ b/src/cmd/compile/internal/amd64/ssa.go
@@ -1125,7 +1125,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		if v.Args[0].Reg() != v.Reg() {
 			// POPCNT on Intel has a false dependency on the destination register.
 			// Xor register with itself to break the dependency.
-			p := s.Prog(x86.AXORQ)
+			p := s.Prog(x86.AXORL)
 			p.From.Type = obj.TYPE_REG
 			p.From.Reg = v.Reg()
 			p.To.Type = obj.TYPE_REG