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diff --git a/src/runtime/memclr_386.s b/src/runtime/memclr_386.s
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+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !plan9
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// See memclrNoHeapPointers Go doc for important implementation constraints.
+
+// func memclrNoHeapPointers(ptr unsafe.Pointer, n uintptr)
+TEXT runtime·memclrNoHeapPointers(SB), NOSPLIT, $0-8
+ MOVL ptr+0(FP), DI
+ MOVL n+4(FP), BX
+ XORL AX, AX
+
+ // MOVOU seems always faster than REP STOSL.
+tail:
+ // BSR+branch table make almost all memmove/memclr benchmarks worse. Not worth doing.
+ TESTL BX, BX
+ JEQ _0
+ CMPL BX, $2
+ JBE _1or2
+ CMPL BX, $4
+ JB _3
+ JE _4
+ CMPL BX, $8
+ JBE _5through8
+ CMPL BX, $16
+ JBE _9through16
+#ifdef GO386_softfloat
+ JMP nosse2
+#endif
+ PXOR X0, X0
+ CMPL BX, $32
+ JBE _17through32
+ CMPL BX, $64
+ JBE _33through64
+ CMPL BX, $128
+ JBE _65through128
+ CMPL BX, $256
+ JBE _129through256
+
+loop:
+ MOVOU X0, 0(DI)
+ MOVOU X0, 16(DI)
+ MOVOU X0, 32(DI)
+ MOVOU X0, 48(DI)
+ MOVOU X0, 64(DI)
+ MOVOU X0, 80(DI)
+ MOVOU X0, 96(DI)
+ MOVOU X0, 112(DI)
+ MOVOU X0, 128(DI)
+ MOVOU X0, 144(DI)
+ MOVOU X0, 160(DI)
+ MOVOU X0, 176(DI)
+ MOVOU X0, 192(DI)
+ MOVOU X0, 208(DI)
+ MOVOU X0, 224(DI)
+ MOVOU X0, 240(DI)
+ SUBL $256, BX
+ ADDL $256, DI
+ CMPL BX, $256
+ JAE loop
+ JMP tail
+
+_1or2:
+ MOVB AX, (DI)
+ MOVB AX, -1(DI)(BX*1)
+ RET
+_0:
+ RET
+_3:
+ MOVW AX, (DI)
+ MOVB AX, 2(DI)
+ RET
+_4:
+ // We need a separate case for 4 to make sure we clear pointers atomically.
+ MOVL AX, (DI)
+ RET
+_5through8:
+ MOVL AX, (DI)
+ MOVL AX, -4(DI)(BX*1)
+ RET
+_9through16:
+ MOVL AX, (DI)
+ MOVL AX, 4(DI)
+ MOVL AX, -8(DI)(BX*1)
+ MOVL AX, -4(DI)(BX*1)
+ RET
+_17through32:
+ MOVOU X0, (DI)
+ MOVOU X0, -16(DI)(BX*1)
+ RET
+_33through64:
+ MOVOU X0, (DI)
+ MOVOU X0, 16(DI)
+ MOVOU X0, -32(DI)(BX*1)
+ MOVOU X0, -16(DI)(BX*1)
+ RET
+_65through128:
+ MOVOU X0, (DI)
+ MOVOU X0, 16(DI)
+ MOVOU X0, 32(DI)
+ MOVOU X0, 48(DI)
+ MOVOU X0, -64(DI)(BX*1)
+ MOVOU X0, -48(DI)(BX*1)
+ MOVOU X0, -32(DI)(BX*1)
+ MOVOU X0, -16(DI)(BX*1)
+ RET
+_129through256:
+ MOVOU X0, (DI)
+ MOVOU X0, 16(DI)
+ MOVOU X0, 32(DI)
+ MOVOU X0, 48(DI)
+ MOVOU X0, 64(DI)
+ MOVOU X0, 80(DI)
+ MOVOU X0, 96(DI)
+ MOVOU X0, 112(DI)
+ MOVOU X0, -128(DI)(BX*1)
+ MOVOU X0, -112(DI)(BX*1)
+ MOVOU X0, -96(DI)(BX*1)
+ MOVOU X0, -80(DI)(BX*1)
+ MOVOU X0, -64(DI)(BX*1)
+ MOVOU X0, -48(DI)(BX*1)
+ MOVOU X0, -32(DI)(BX*1)
+ MOVOU X0, -16(DI)(BX*1)
+ RET
+nosse2:
+ MOVL BX, CX
+ SHRL $2, CX
+ REP
+ STOSL
+ ANDL $3, BX
+ JNE tail
+ RET