From bad852b61b79503fcb3c5fc379c70f768df3e1fb Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Sat, 23 Oct 2021 01:26:47 -0400
Subject: [PATCH] x86: Replace sse2 instructions with avx in
 memcmp-evex-movbe.S
Content-type: text/plain; charset=UTF-8

This commit replaces two usages of SSE2 'movups' with AVX 'vmovdqu'.

it could potentially be dangerous to use SSE2 if this function is ever
called without using 'vzeroupper' beforehand. While compilers appear
to use 'vzeroupper' before function calls if AVX2 has been used, using
SSE2 here is more brittle. Since it is not absolutely necessary it
should be avoided.

It costs 2-extra bytes but the extra bytes should only eat into
alignment padding.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---
 sysdeps/x86_64/multiarch/memcmp-evex-movbe.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
index 2761b54f..640f6757 100644
--- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
+++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S
@@ -561,13 +561,13 @@ L(between_16_31):
 	/* From 16 to 31 bytes.  No branch when size == 16.  */
 
 	/* Use movups to save code size.  */
-	movups	(%rsi), %xmm2
+	vmovdqu	(%rsi), %xmm2
 	VPCMP	$4, (%rdi), %xmm2, %k1
 	kmovd	%k1, %eax
 	testl	%eax, %eax
 	jnz	L(return_vec_0_lv)
 	/* Use overlapping loads to avoid branches.  */
-	movups	-16(%rsi, %rdx, CHAR_SIZE), %xmm2
+	vmovdqu	-16(%rsi, %rdx, CHAR_SIZE), %xmm2
 	VPCMP	$4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1
 	addl	$(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx
 	kmovd	%k1, %eax
-- 
GitLab

