diff --git a/s2/_generate/gen.go b/s2/_generate/gen.go
index 6b480af39b..6c06969ea9 100644
--- a/s2/_generate/gen.go
+++ b/s2/_generate/gen.go
@@ -1501,6 +1501,7 @@ func (o options) genEmitLiteral() {
 	Pragma("noescape")
 
 	dstBase, litBase, litLen, retval := GP64(), GP64(), GP64(), GP64()
+	restore := saveBP()
 	Load(Param("lit").Len(), litLen)
 	Load(Param("dst").Base(), dstBase)
 	Load(Param("lit").Base(), litBase)
@@ -1513,6 +1514,7 @@ func (o options) genEmitLiteral() {
 
 	Label("emit_literal_end_standalone")
 	Store(retval, ReturnIndex(0))
+	restore()
 	RET()
 
 }
@@ -1669,6 +1671,7 @@ func (o options) genEmitRepeat() {
 	Pragma("noescape")
 
 	dstBase, offset, length, retval := GP64(), GP64(), GP64(), GP64()
+	restore := saveBP()
 
 	// retval = 0
 	XORQ(retval, retval)
@@ -1679,6 +1682,7 @@ func (o options) genEmitRepeat() {
 	o.emitRepeat("standalone", length, offset, retval, dstBase, LabelRef("gen_emit_repeat_end"))
 	Label("gen_emit_repeat_end")
 	Store(retval, ReturnIndex(0))
+	restore()
 	RET()
 }
 
@@ -1824,16 +1828,17 @@ func (o options) genEmitCopy() {
 	Pragma("noescape")
 
 	dstBase, offset, length, retval := GP64(), GP64(), GP64(), GP64()
+	restore := saveBP()
 
 	//	i := 0
 	XORQ(retval, retval)
-
 	Load(Param("dst").Base(), dstBase)
 	Load(Param("offset"), offset)
 	Load(Param("length"), length)
 	o.emitCopy("standalone", length, offset, retval, dstBase, LabelRef("gen_emit_copy_end"))
 	Label("gen_emit_copy_end")
 	Store(retval, ReturnIndex(0))
+	restore()
 	RET()
 }
 
@@ -1855,6 +1860,7 @@ func (o options) genEmitCopyNoRepeat() {
 	Pragma("noescape")
 
 	dstBase, offset, length, retval := GP64(), GP64(), GP64(), GP64()
+	restore := saveBP()
 
 	//	i := 0
 	XORQ(retval, retval)
@@ -1865,6 +1871,7 @@ func (o options) genEmitCopyNoRepeat() {
 	o.emitCopy("standalone_snappy", length, offset, retval, dstBase, "gen_emit_copy_end_snappy")
 	Label("gen_emit_copy_end_snappy")
 	Store(retval, ReturnIndex(0))
+	restore()
 	RET()
 }
 
@@ -2368,12 +2375,15 @@ func (o options) genMatchLen() {
 
 	aBase, bBase, length := GP64(), GP64(), GP64()
 
+	restore := saveBP()
+
 	Load(Param("a").Base(), aBase)
 	Load(Param("b").Base(), bBase)
 	Load(Param("a").Len(), length)
 	l := o.matchLen("standalone", aBase, bBase, length, LabelRef("gen_match_len_end"))
 	Label("gen_match_len_end")
 	Store(l.As64(), ReturnIndex(0))
+	restore()
 	RET()
 }
 
@@ -2519,3 +2529,12 @@ func (o options) matchLenAlt(name string, a, b, len reg.GPVirtual, end LabelRef)
 	JMP(end)
 	return matched
 }
+
+// saveBP will save RBP in an XMM register and restore it when returning.
+func saveBP() (restore func()) {
+	x := XMM()
+	MOVQ(reg.RBP, x)
+	return func() {
+		MOVQ(x, reg.RBP)
+	}
+}
diff --git a/s2/encodeblock_amd64.s b/s2/encodeblock_amd64.s
index 748c1c2e20..f065b48da1 100644
--- a/s2/encodeblock_amd64.s
+++ b/s2/encodeblock_amd64.s
@@ -12603,221 +12603,224 @@ gen_emit_repeat_end:
 	RET
 
 // func emitCopy(dst []byte, offset int, length int) int
+// Requires: SSE2
 TEXT ·emitCopy(SB), NOSPLIT, $0-48
-	XORQ BX, BX
-	MOVQ dst_base+0(FP), AX
-	MOVQ offset+24(FP), CX
-	MOVQ length+32(FP), DX
+	XORQ AX, AX
+	MOVQ BP, X0
+	MOVQ dst_base+0(FP), CX
+	MOVQ offset+24(FP), DX
+	MOVQ length+32(FP), BX
 
 	// emitCopy
-	CMPL CX, $0x00010000
+	CMPL DX, $0x00010000
 	JL   two_byte_offset_standalone
 
 four_bytes_loop_back_standalone:
-	CMPL DX, $0x40
+	CMPL BX, $0x40
 	JLE  four_bytes_remain_standalone
-	MOVB $0xff, (AX)
-	MOVL CX, 1(AX)
-	LEAL -64(DX), DX
-	ADDQ $0x05, BX
+	MOVB $0xff, (CX)
+	MOVL DX, 1(CX)
+	LEAL -64(BX), BX
 	ADDQ $0x05, AX
-	CMPL DX, $0x04
+	ADDQ $0x05, CX
+	CMPL BX, $0x04
 	JL   four_bytes_remain_standalone
 
 	// emitRepeat
 emit_repeat_again_standalone_emit_copy:
-	MOVL DX, BP
-	LEAL -4(DX), DX
+	MOVL BX, BP
+	LEAL -4(BX), BX
 	CMPL BP, $0x08
 	JLE  repeat_two_standalone_emit_copy
 	CMPL BP, $0x0c
 	JGE  cant_repeat_two_offset_standalone_emit_copy
-	CMPL CX, $0x00000800
+	CMPL DX, $0x00000800
 	JLT  repeat_two_offset_standalone_emit_copy
 
 cant_repeat_two_offset_standalone_emit_copy:
-	CMPL DX, $0x00000104
+	CMPL BX, $0x00000104
 	JLT  repeat_three_standalone_emit_copy
-	CMPL DX, $0x00010100
+	CMPL BX, $0x00010100
 	JLT  repeat_four_standalone_emit_copy
-	CMPL DX, $0x0100ffff
+	CMPL BX, $0x0100ffff
 	JLT  repeat_five_standalone_emit_copy
-	LEAL -16842747(DX), DX
-	MOVW $0x001d, (AX)
-	MOVW $0xfffb, 2(AX)
-	MOVB $0xff, 4(AX)
+	LEAL -16842747(BX), BX
+	MOVW $0x001d, (CX)
+	MOVW $0xfffb, 2(CX)
+	MOVB $0xff, 4(CX)
+	ADDQ $0x05, CX
 	ADDQ $0x05, AX
-	ADDQ $0x05, BX
 	JMP  emit_repeat_again_standalone_emit_copy
 
 repeat_five_standalone_emit_copy:
-	LEAL -65536(DX), DX
-	MOVL DX, CX
-	MOVW $0x001d, (AX)
-	MOVW DX, 2(AX)
-	SARL $0x10, CX
-	MOVB CL, 4(AX)
-	ADDQ $0x05, BX
+	LEAL -65536(BX), BX
+	MOVL BX, DX
+	MOVW $0x001d, (CX)
+	MOVW BX, 2(CX)
+	SARL $0x10, DX
+	MOVB DL, 4(CX)
 	ADDQ $0x05, AX
+	ADDQ $0x05, CX
 	JMP  gen_emit_copy_end
 
 repeat_four_standalone_emit_copy:
-	LEAL -256(DX), DX
-	MOVW $0x0019, (AX)
-	MOVW DX, 2(AX)
-	ADDQ $0x04, BX
+	LEAL -256(BX), BX
+	MOVW $0x0019, (CX)
+	MOVW BX, 2(CX)
 	ADDQ $0x04, AX
+	ADDQ $0x04, CX
 	JMP  gen_emit_copy_end
 
 repeat_three_standalone_emit_copy:
-	LEAL -4(DX), DX
-	MOVW $0x0015, (AX)
-	MOVB DL, 2(AX)
-	ADDQ $0x03, BX
+	LEAL -4(BX), BX
+	MOVW $0x0015, (CX)
+	MOVB BL, 2(CX)
 	ADDQ $0x03, AX
+	ADDQ $0x03, CX
 	JMP  gen_emit_copy_end
 
 repeat_two_standalone_emit_copy:
-	SHLL $0x02, DX
-	ORL  $0x01, DX
-	MOVW DX, (AX)
-	ADDQ $0x02, BX
+	SHLL $0x02, BX
+	ORL  $0x01, BX
+	MOVW BX, (CX)
 	ADDQ $0x02, AX
+	ADDQ $0x02, CX
 	JMP  gen_emit_copy_end
 
 repeat_two_offset_standalone_emit_copy:
 	XORQ BP, BP
-	LEAL 1(BP)(DX*4), DX
-	MOVB CL, 1(AX)
-	SARL $0x08, CX
-	SHLL $0x05, CX
-	ORL  CX, DX
-	MOVB DL, (AX)
-	ADDQ $0x02, BX
-	ADDQ $0x02, AX
+	LEAL 1(BP)(BX*4), BX
+	MOVB DL, 1(CX)
+	SARL $0x08, DX
+	SHLL $0x05, DX
+	ORL  DX, BX
+	MOVB BL, (CX)
+	ADDQ $0x02, AX
+	ADDQ $0x02, CX
 	JMP  gen_emit_copy_end
 	JMP four_bytes_loop_back_standalone
 
 four_bytes_remain_standalone:
-	TESTL DX, DX
+	TESTL BX, BX
 	JZ    gen_emit_copy_end
 	MOVB  $0x03, BP
-	LEAL  -4(BP)(DX*4), DX
-	MOVB  DL, (AX)
-	MOVL  CX, 1(AX)
-	ADDQ  $0x05, BX
+	LEAL  -4(BP)(BX*4), BX
+	MOVB  BL, (CX)
+	MOVL  DX, 1(CX)
 	ADDQ  $0x05, AX
+	ADDQ  $0x05, CX
 	JMP   gen_emit_copy_end
 
 two_byte_offset_standalone:
-	CMPL DX, $0x40
+	CMPL BX, $0x40
 	JLE  two_byte_offset_short_standalone
-	MOVB $0xee, (AX)
-	MOVW CX, 1(AX)
-	LEAL -60(DX), DX
+	MOVB $0xee, (CX)
+	MOVW DX, 1(CX)
+	LEAL -60(BX), BX
+	ADDQ $0x03, CX
 	ADDQ $0x03, AX
-	ADDQ $0x03, BX
 
 	// emitRepeat
 emit_repeat_again_standalone_emit_copy_short:
-	MOVL DX, BP
-	LEAL -4(DX), DX
+	MOVL BX, BP
+	LEAL -4(BX), BX
 	CMPL BP, $0x08
 	JLE  repeat_two_standalone_emit_copy_short
 	CMPL BP, $0x0c
 	JGE  cant_repeat_two_offset_standalone_emit_copy_short
-	CMPL CX, $0x00000800
+	CMPL DX, $0x00000800
 	JLT  repeat_two_offset_standalone_emit_copy_short
 
 cant_repeat_two_offset_standalone_emit_copy_short:
-	CMPL DX, $0x00000104
+	CMPL BX, $0x00000104
 	JLT  repeat_three_standalone_emit_copy_short
-	CMPL DX, $0x00010100
+	CMPL BX, $0x00010100
 	JLT  repeat_four_standalone_emit_copy_short
-	CMPL DX, $0x0100ffff
+	CMPL BX, $0x0100ffff
 	JLT  repeat_five_standalone_emit_copy_short
-	LEAL -16842747(DX), DX
-	MOVW $0x001d, (AX)
-	MOVW $0xfffb, 2(AX)
-	MOVB $0xff, 4(AX)
+	LEAL -16842747(BX), BX
+	MOVW $0x001d, (CX)
+	MOVW $0xfffb, 2(CX)
+	MOVB $0xff, 4(CX)
+	ADDQ $0x05, CX
 	ADDQ $0x05, AX
-	ADDQ $0x05, BX
 	JMP  emit_repeat_again_standalone_emit_copy_short
 
 repeat_five_standalone_emit_copy_short:
-	LEAL -65536(DX), DX
-	MOVL DX, CX
-	MOVW $0x001d, (AX)
-	MOVW DX, 2(AX)
-	SARL $0x10, CX
-	MOVB CL, 4(AX)
-	ADDQ $0x05, BX
+	LEAL -65536(BX), BX
+	MOVL BX, DX
+	MOVW $0x001d, (CX)
+	MOVW BX, 2(CX)
+	SARL $0x10, DX
+	MOVB DL, 4(CX)
 	ADDQ $0x05, AX
+	ADDQ $0x05, CX
 	JMP  gen_emit_copy_end
 
 repeat_four_standalone_emit_copy_short:
-	LEAL -256(DX), DX
-	MOVW $0x0019, (AX)
-	MOVW DX, 2(AX)
-	ADDQ $0x04, BX
+	LEAL -256(BX), BX
+	MOVW $0x0019, (CX)
+	MOVW BX, 2(CX)
 	ADDQ $0x04, AX
+	ADDQ $0x04, CX
 	JMP  gen_emit_copy_end
 
 repeat_three_standalone_emit_copy_short:
-	LEAL -4(DX), DX
-	MOVW $0x0015, (AX)
-	MOVB DL, 2(AX)
-	ADDQ $0x03, BX
+	LEAL -4(BX), BX
+	MOVW $0x0015, (CX)
+	MOVB BL, 2(CX)
 	ADDQ $0x03, AX
+	ADDQ $0x03, CX
 	JMP  gen_emit_copy_end
 
 repeat_two_standalone_emit_copy_short:
-	SHLL $0x02, DX
-	ORL  $0x01, DX
-	MOVW DX, (AX)
-	ADDQ $0x02, BX
+	SHLL $0x02, BX
+	ORL  $0x01, BX
+	MOVW BX, (CX)
 	ADDQ $0x02, AX
+	ADDQ $0x02, CX
 	JMP  gen_emit_copy_end
 
 repeat_two_offset_standalone_emit_copy_short:
 	XORQ BP, BP
-	LEAL 1(BP)(DX*4), DX
-	MOVB CL, 1(AX)
-	SARL $0x08, CX
-	SHLL $0x05, CX
-	ORL  CX, DX
-	MOVB DL, (AX)
-	ADDQ $0x02, BX
-	ADDQ $0x02, AX
+	LEAL 1(BP)(BX*4), BX
+	MOVB DL, 1(CX)
+	SARL $0x08, DX
+	SHLL $0x05, DX
+	ORL  DX, BX
+	MOVB BL, (CX)
+	ADDQ $0x02, AX
+	ADDQ $0x02, CX
 	JMP  gen_emit_copy_end
 	JMP two_byte_offset_standalone
 
 two_byte_offset_short_standalone:
-	CMPL DX, $0x0c
+	CMPL BX, $0x0c
 	JGE  emit_copy_three_standalone
-	CMPL CX, $0x00000800
+	CMPL DX, $0x00000800
 	JGE  emit_copy_three_standalone
 	MOVB $0x01, BP
-	LEAL -16(BP)(DX*4), DX
-	MOVB CL, 1(AX)
-	SHRL $0x08, CX
-	SHLL $0x05, CX
-	ORL  CX, DX
-	MOVB DL, (AX)
-	ADDQ $0x02, BX
-	ADDQ $0x02, AX
+	LEAL -16(BP)(BX*4), BX
+	MOVB DL, 1(CX)
+	SHRL $0x08, DX
+	SHLL $0x05, DX
+	ORL  DX, BX
+	MOVB BL, (CX)
+	ADDQ $0x02, AX
+	ADDQ $0x02, CX
 	JMP  gen_emit_copy_end
 
 emit_copy_three_standalone:
 	MOVB $0x02, BP
-	LEAL -4(BP)(DX*4), DX
-	MOVB DL, (AX)
-	MOVW CX, 1(AX)
-	ADDQ $0x03, BX
+	LEAL -4(BP)(BX*4), BX
+	MOVB BL, (CX)
+	MOVW DX, 1(CX)
 	ADDQ $0x03, AX
+	ADDQ $0x03, CX
 
 gen_emit_copy_end:
-	MOVQ BX, ret+40(FP)
+	MOVQ AX, ret+40(FP)
+	MOVQ X0, BP
 	RET
 
 // func emitCopyNoRepeat(dst []byte, offset int, length int) int