Blame SOURCES/0001-void-short-distance-rep-movsb.patch

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From ff7e299914a2dfa1c3fd7abd267535f7586ac413 Mon Sep 17 00:00:00 2001
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From: Wangyang Guo <wangyang.guo@intel.com>
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Date: Mon, 15 Nov 2021 06:12:16 +0000
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Subject: [PATCH 1/2] Avoid short distance rep movsb
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---
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 .../multiarch/memmove-vec-unaligned-erms.S    | 22 +++++++++++++++++++
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 1 file changed, 22 insertions(+)
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diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
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index c952576c..07299dc0 100644
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--- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
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+++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
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@@ -56,6 +56,14 @@
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 # endif
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 #endif
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+/* Avoid short distance rep movsb only with non-SSE vector.  */
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+#ifndef AVOID_SHORT_DISTANCE_REP_MOVSB
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+# define AVOID_SHORT_DISTANCE_REP_MOVSB 1
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+#else
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+# define AVOID_SHORT_DISTANCE_REP_MOVSB 0
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+#endif
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+
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+
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 #ifndef PREFETCH
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 # define PREFETCH(addr) prefetcht0 addr
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 #endif
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@@ -235,7 +243,21 @@ L(movsb):
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 	cmpq	%r9, %rdi
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 	/* Avoid slow backward REP MOVSB.  */
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 	jb	L(more_8x_vec_backward)
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+# if AVOID_SHORT_DISTANCE_REP_MOVSB
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+	movq	%rdi, %rcx
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+	subq	%rsi, %rcx
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+	jmp	2f
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+# endif
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 1:
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+# if AVOID_SHORT_DISTANCE_REP_MOVSB
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+	movq	%rsi, %rcx
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+	subq	%rdi, %rcx
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+2:
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+/* Avoid "rep movsb" if RCX, the distance between source and destination,
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+   is N*4GB + [1..63] with N >= 0.  */
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+	cmpl	$63, %ecx
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+	jbe	L(more_2x_vec)	/* Avoid "rep movsb" if ECX <= 63.  */
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+# endif
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 	movq	%rdx, %rcx
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 	rep movsb
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 L(nop):
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-- 
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2.27.0
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