8a, 8l: add CMPXCHG8B, XADDB, XADDL, XADDW

R=ken2
CC=golang-dev
https://golang.org/cl/4240041

src/cmd/8a/lex.c

@@ -332,6 +332,7 @@ struct
 	"CMPSB",	LTYPE0,	ACMPSB,
 	"CMPSL",	LTYPE0,	ACMPSL,
 	"CMPSW",	LTYPE0,	ACMPSW,
+	"CMPXCHG8B",	LTYPE1,	ACMPXCHG8B,
 	"CMPXCHGB",	LTYPE3,	ACMPXCHGB,
 	"CMPXCHGL",	LTYPE3,	ACMPXCHGL,
 	"CMPXCHGW",	LTYPE3,	ACMPXCHGW,
@@ -546,6 +547,9 @@ struct
 	"VERW",		LTYPE2,	AVERW,
 	"WAIT",		LTYPE0,	AWAIT,
 	"WORD",		LTYPE2,	AWORD,
+	"XADDB",	LTYPE3,	AXADDB,
+	"XADDL",	LTYPE3,	AXADDL,
+	"XADDW",	LTYPE3,	AXADDW,
 	"XCHGB",	LTYPE3,	AXCHGB,
 	"XCHGL",	LTYPE3,	AXCHGL,
 	"XCHGW",	LTYPE3,	AXCHGW,

src/cmd/8l/8.out.h

@@ -392,6 +392,11 @@ enum	as
 	ACMPXCHGB,
 	ACMPXCHGL,
 	ACMPXCHGW,
+	ACMPXCHG8B,
+	
+	AXADDB,
+	AXADDL,
+	AXADDW,
 
 	/* conditional move */
 	ACMOVLCC,

src/cmd/8l/optab.c

@@ -702,6 +702,11 @@ Optab optab[] =
 	{ ACMPXCHGB,	yrb_mb,	Pm, 0xb0 },
 	{ ACMPXCHGL,	yrl_ml,	Pm, 0xb1 },
 	{ ACMPXCHGW,	yrl_ml,	Pm, 0xb1 },
+	{ ACMPXCHG8B,	yscond,	Pm, 0xc7,(01) },
+
+	{ AXADDB,	yrb_mb,	Pb, 0x0f,0xc0 },
+	{ AXADDL,	yrl_ml,	Pm, 0xc1 },
+	{ AXADDW,	yrl_ml,	Pe, 0x0f,0xc1 },
 
 	{ ACMOVLCC,	yml_rl,	Pm, 0x43 },
 	{ ACMOVLCS,	yml_rl,	Pm, 0x42 },