[PATCH v1 2/3] x86: Move and slightly improve memset_erms

[Noah Goldstein]

Implementation wise:
    1. Remove the VZEROUPPER as memset_{impl}_unaligned_erms does not
       use the L(stosb) label that was previously defined.

    2. Don't give the hotpath (fallthrough) to zero size.

Code positioning wise:

Move L(memset_{chk}_erms) to its own file.  Leaving it in between the
memset_{impl}_unaligned both adds unnecessary complexity to the
file and wastes space in a relatively hot cache section.
---
 .../multiarch/memset-vec-unaligned-erms.S     | 54 ++++++++-----------
 1 file changed, 23 insertions(+), 31 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
index abc12d9cda..d98c613651 100644
--- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
@@ -156,37 +156,6 @@ L(entry_from_wmemset):
 #if defined USE_MULTIARCH && IS_IN (libc)
 END (MEMSET_SYMBOL (__memset, unaligned))
 
-# if VEC_SIZE == 16
-ENTRY (__memset_chk_erms)
-	cmp	%RDX_LP, %RCX_LP
-	jb	HIDDEN_JUMPTARGET (__chk_fail)
-END (__memset_chk_erms)
-
-/* Only used to measure performance of REP STOSB.  */
-ENTRY (__memset_erms)
-	/* Skip zero length.  */
-	test	%RDX_LP, %RDX_LP
-	jnz	 L(stosb)
-	movq	%rdi, %rax
-	ret
-# else
-/* Provide a hidden symbol to debugger.  */
-	.hidden	MEMSET_SYMBOL (__memset, erms)
-ENTRY (MEMSET_SYMBOL (__memset, erms))
-# endif
-L(stosb):
-	mov	%RDX_LP, %RCX_LP
-	movzbl	%sil, %eax
-	mov	%RDI_LP, %RDX_LP
-	rep stosb
-	mov	%RDX_LP, %RAX_LP
-	VZEROUPPER_RETURN
-# if VEC_SIZE == 16
-END (__memset_erms)
-# else
-END (MEMSET_SYMBOL (__memset, erms))
-# endif
-
 # if defined SHARED && IS_IN (libc)
 ENTRY_CHK (MEMSET_CHK_SYMBOL (__memset_chk, unaligned_erms))
 	cmp	%RDX_LP, %RCX_LP
@@ -461,3 +430,26 @@ L(between_2_3):
 #endif
 	ret
 END (MEMSET_SYMBOL (__memset, unaligned_erms))
+
+#if defined USE_MULTIARCH && IS_IN (libc) && VEC_SIZE == 16
+ENTRY (__memset_chk_erms)
+	cmp	%RDX_LP, %RCX_LP
+	jb	HIDDEN_JUMPTARGET (__chk_fail)
+END (__memset_chk_erms)
+
+/* Only used to measure performance of REP STOSB.  */
+ENTRY (__memset_erms)
+	/* Skip zero length.  */
+	test	%RDX_LP, %RDX_LP
+	jz	 L(stosb_return_zero)
+	mov	%RDX_LP, %RCX_LP
+	movzbl	%sil, %eax
+	mov	%RDI_LP, %RDX_LP
+	rep stosb
+	mov	%RDX_LP, %RAX_LP
+	ret
+L(stosb_return_zero):
+	movq	%rdi, %rax
+	ret
+END (__memset_erms)
+#endif
-- 
2.34.1