From bc9e160443f33f979aeb79dd92ac73876841e36e Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Fri, 1 Aug 2014 06:21:08 -0700
Subject: [PATCH] runtime: prevent pointless jmp in amd64 and 386 memmove

6a and 8a rearrange memmove such that the fallthrough from move_1or2 to move_0 ends up being a JMP to a RET. Insert an explicit RET to prevent such silliness.

Do the same for memclr as prophylaxis.

benchmark                old ns/op     new ns/op     delta
BenchmarkMemmove1        4.59          4.13          -10.02%
BenchmarkMemmove2        4.58          4.13          -9.83%

LGTM=khr
R=golang-codereviews, dvyukov, minux, ruiu, bradfitz, khr
CC=golang-codereviews
https://golang.org/cl/120930043
---
 src/pkg/runtime/memclr_386.s          | 1 +
 src/pkg/runtime/memclr_amd64.s        | 1 +
 src/pkg/runtime/memclr_plan9_386.s    | 1 +
 src/pkg/runtime/memmove_386.s         | 1 +
 src/pkg/runtime/memmove_amd64.s       | 1 +
 src/pkg/runtime/memmove_plan9_386.s   | 1 +
 src/pkg/runtime/memmove_plan9_amd64.s | 1 +
 7 files changed, 7 insertions(+)

diff --git a/src/pkg/runtime/memclr_386.s b/src/pkg/runtime/memclr_386.s
index 4b7580cb49..aeabad413e 100644
--- a/src/pkg/runtime/memclr_386.s
+++ b/src/pkg/runtime/memclr_386.s
@@ -63,6 +63,7 @@ clr_loop:
 clr_1or2:
 	MOVB	AX, (DI)
 	MOVB	AX, -1(DI)(BX*1)
+	RET
 clr_0:
 	RET
 clr_3or4:
diff --git a/src/pkg/runtime/memclr_amd64.s b/src/pkg/runtime/memclr_amd64.s
index 6b79363b24..01c6a415c0 100644
--- a/src/pkg/runtime/memclr_amd64.s
+++ b/src/pkg/runtime/memclr_amd64.s
@@ -62,6 +62,7 @@ clr_loop:
 clr_1or2:
 	MOVB	AX, (DI)
 	MOVB	AX, -1(DI)(BX*1)
+	RET
 clr_0:
 	RET
 clr_3or4:
diff --git a/src/pkg/runtime/memclr_plan9_386.s b/src/pkg/runtime/memclr_plan9_386.s
index 9b496785a2..ed5dbbd3c6 100644
--- a/src/pkg/runtime/memclr_plan9_386.s
+++ b/src/pkg/runtime/memclr_plan9_386.s
@@ -32,6 +32,7 @@ clr_tail:
 clr_1or2:
 	MOVB	AX, (DI)
 	MOVB	AX, -1(DI)(BX*1)
+	RET
 clr_0:
 	RET
 clr_3or4:
diff --git a/src/pkg/runtime/memmove_386.s b/src/pkg/runtime/memmove_386.s
index 1fd9ba2bcc..51b08d56d3 100644
--- a/src/pkg/runtime/memmove_386.s
+++ b/src/pkg/runtime/memmove_386.s
@@ -115,6 +115,7 @@ move_1or2:
 	MOVB	-1(SI)(BX*1), CX
 	MOVB	AX, (DI)
 	MOVB	CX, -1(DI)(BX*1)
+	RET
 move_0:
 	RET
 move_3or4:
diff --git a/src/pkg/runtime/memmove_amd64.s b/src/pkg/runtime/memmove_amd64.s
index 672fce90b3..339c5dd410 100644
--- a/src/pkg/runtime/memmove_amd64.s
+++ b/src/pkg/runtime/memmove_amd64.s
@@ -122,6 +122,7 @@ move_1or2:
 	MOVB	-1(SI)(BX*1), CX
 	MOVB	AX, (DI)
 	MOVB	CX, -1(DI)(BX*1)
+	RET
 move_0:
 	RET
 move_3or4:
diff --git a/src/pkg/runtime/memmove_plan9_386.s b/src/pkg/runtime/memmove_plan9_386.s
index 187616cd0a..5ac5c27d40 100644
--- a/src/pkg/runtime/memmove_plan9_386.s
+++ b/src/pkg/runtime/memmove_plan9_386.s
@@ -101,6 +101,7 @@ move_1or2:
 	MOVB	-1(SI)(BX*1), CX
 	MOVB	AX, (DI)
 	MOVB	CX, -1(DI)(BX*1)
+	RET
 move_0:
 	RET
 move_3or4:
diff --git a/src/pkg/runtime/memmove_plan9_amd64.s b/src/pkg/runtime/memmove_plan9_amd64.s
index 60108273cf..3664e45ae2 100644
--- a/src/pkg/runtime/memmove_plan9_amd64.s
+++ b/src/pkg/runtime/memmove_plan9_amd64.s
@@ -104,6 +104,7 @@ move_1or2:
 	MOVB	-1(SI)(BX*1), CX
 	MOVB	AX, (DI)
 	MOVB	CX, -1(DI)(BX*1)
+	RET
 move_0:
 	RET
 move_3or4:
-- 
2.48.1