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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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