cmd/5a, cmd/5l, math: add CLZ instruction for ARM

        Supported in ARMv5 and above.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6284043

src/cmd/5a/lex.c

@@ -406,6 +406,8 @@ struct
 
 	"PLD",		LTYPEPLD, APLD,
 	"UNDEF",	LTYPEE,	AUNDEF,
+	"CLZ",		LTYPE2, ACLZ,
+
 	0
 };
 

src/cmd/5l/5.out.h

@@ -184,9 +184,11 @@ enum	as
 	ASTREXD,
 
 	APLD,
-	
+
 	AUNDEF,
 
+	ACLZ,
+
 	ALAST,
 };
 

src/cmd/5l/asm.c

@@ -1801,6 +1801,11 @@ if(debug['G']) print("%ux: %s: arm %d\n", (uint32)(p->pc), p->from.sym->name, p-
 		o1 = opbra(ABL, C_SCOND_NONE);
 		o1 |= (v >> 2) & 0xffffff;
 		break;
+	case 97:	/* CLZ Rm, Rd */
+ 		o1 = oprrr(p->as, p->scond);
+ 		o1 |= p->to.reg << 12;
+ 		o1 |= p->from.reg;
+		break;
 	}
 	
 	out[0] = o1;
@@ -1958,6 +1963,10 @@ oprrr(int a, int sc)
 		return o | (0xe<<24) | (0x1<<20) | (0xb<<8) | (1<<4);
 	case ACMP+AEND:	// cmp imm
 		return o | (0x3<<24) | (0x5<<20);
+
+	case ACLZ:
+		// CLZ doesn't support .S
+		return (o & (0xf<<28)) | (0x16f<<16) | (0xf1<<4);
 	}
 	diag("bad rrr %d", a);
 	prasm(curp);

src/cmd/5l/optab.c

@@ -236,5 +236,7 @@ Optab	optab[] =
 	
 	{ AUNDEF,		C_NONE,	C_NONE,	C_NONE,		96, 4, 0 },
 
+	{ ACLZ,		C_REG,	C_NONE,	C_REG,		97, 4, 0 },
+
 	{ AXXX,		C_NONE,	C_NONE,	C_NONE,		 0, 4, 0 },
 };

src/cmd/5l/span.c

@@ -848,6 +848,7 @@ buildop(void)
 		case ATST:
 		case APLD:
 		case AUNDEF:
+		case ACLZ:
 			break;
 		}
 	}

src/pkg/math/big/arith_arm.s

@@ -314,7 +314,7 @@ TEXT ·mulWW(SB),7,$0
 // func bitLen(x Word) (n int)
 TEXT ·bitLen(SB),7,$0
 	MOVW	x+0(FP), R0
-	WORD	$0xe16f0f10 // CLZ R0, R0  (count leading zeros)
+	CLZ 	R0, R0
 	MOVW	$32, R1
 	SUB.S	R0, R1
 	MOVW	R1, n+4(FP)