8a, 8l: add PREFETCH instructions

R=ken2
CC=golang-dev
https://golang.org/cl/5992082

src/cmd/8a/lex.c

@@ -667,6 +667,10 @@ struct
 	"MFENCE",	LTYPE0, AMFENCE,
 	"SFENCE",	LTYPE0, ASFENCE,
 	"EMMS",		LTYPE0, AEMMS,
+	"PREFETCHT0",		LTYPE2,	APREFETCHT0,
+	"PREFETCHT1",		LTYPE2,	APREFETCHT1,
+	"PREFETCHT2",		LTYPE2,	APREFETCHT2,
+	"PREFETCHNTA",		LTYPE2,	APREFETCHNTA,
 
 	0
 };

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

@@ -451,6 +451,11 @@ enum	as
 	ASFENCE,
 
 	AEMMS,
+	
+	APREFETCHT0,
+	APREFETCHT1,
+	APREFETCHT2,
+	APREFETCHNTA,
 
 	ALAST
 };

src/cmd/8l/optab.c

@@ -349,6 +349,11 @@ uchar	ysvrs[] =
 	Ym,	Ynone,	Zm_o,	2,
 	0
 };
+uchar	yprefetch[] =
+{
+	Ym,	Ynone,	Zm_o,	2,
+	0,
+};
 
 Optab optab[] =
 /*	as, ytab, andproto, opcode */
@@ -761,5 +766,10 @@ Optab optab[] =
 
 	{ AEMMS, ynone, Pm, 0x77 },
 
+	{ APREFETCHT0,	yprefetch,	Pm,	0x18,(01) },
+	{ APREFETCHT1,	yprefetch,	Pm,	0x18,(02) },
+	{ APREFETCHT2,	yprefetch,	Pm,	0x18,(03) },
+	{ APREFETCHNTA,	yprefetch,	Pm,	0x18,(00) },
+
 	0
 };

src/pkg/runtime/asm_386.s

@@ -417,8 +417,7 @@ TEXT runtime·atomicstore64(SB), 7, $0
 
 TEXT runtime·prefetch(SB), 7, $0
 	MOVL    4(SP), AX
-	// PREFETCHNTA (AX)
-	BYTE $0x0f; BYTE $0x18; BYTE $0x00
+	PREFETCHNTA (AX)
 	RET
 
 // void jmpdefer(fn, sp);