liblink: renumber ARM conditions to make C_SCOND_NONE == 0

A step toward making the zero Prog useful.

Change-Id: I427b98b1ce9bd8f093da825aa4bb83244fc01903
Reviewed-on: https://go-review.googlesource.com/3573Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/5a/a.h

@@ -95,7 +95,7 @@ enum
 	CMACRO,
 	CPREPROC,
 	
-	Always	= 14,
+	Always = C_SCOND_NONE,
 };
 
 EXTERN	int	debug[256];

src/cmd/5a/a.y

@@ -295,7 +295,7 @@ inst:
 		g.offset =
 			(0xe << 24) |		/* opcode */
 			($1 << 20) |		/* MCR/MRC */
-			($2 << 28) |		/* scond */
+			(($2^C_SCOND_XOR) << 28) |		/* scond */
 			(($3 & 15) << 8) |	/* coprocessor number */
 			(($5 & 7) << 21) |	/* coprocessor operation */
 			(($7 & 15) << 12) |	/* arm register */

src/cmd/5a/lex.c

@@ -255,23 +255,23 @@ struct
 	"FPSR",		LFCR,	REG_FPSR,
 	"FPCR",		LFCR,	REG_FPCR,
 
-	".EQ",		LCOND,	0,
-	".NE",		LCOND,	1,
-	".CS",		LCOND,	2,
-	".HS",		LCOND,	2,
-	".CC",		LCOND,	3,
-	".LO",		LCOND,	3,
-	".MI",		LCOND,	4,
-	".PL",		LCOND,	5,
-	".VS",		LCOND,	6,
-	".VC",		LCOND,	7,
-	".HI",		LCOND,	8,
-	".LS",		LCOND,	9,
-	".GE",		LCOND,	10,
-	".LT",		LCOND,	11,
-	".GT",		LCOND,	12,
-	".LE",		LCOND,	13,
-	".AL",		LCOND,	Always,
+	".EQ",		LCOND,	C_SCOND_EQ,
+	".NE",		LCOND,	C_SCOND_NE,
+	".CS",		LCOND,	C_SCOND_HS,
+	".HS",		LCOND,	C_SCOND_HS,
+	".CC",		LCOND,	C_SCOND_LO,
+	".LO",		LCOND,	C_SCOND_LO,
+	".MI",		LCOND,	C_SCOND_MI,
+	".PL",		LCOND,	C_SCOND_PL,
+	".VS",		LCOND,	C_SCOND_VS,
+	".VC",		LCOND,	C_SCOND_VC,
+	".HI",		LCOND,	C_SCOND_HI,
+	".LS",		LCOND,	C_SCOND_LS,
+	".GE",		LCOND,	C_SCOND_GE,
+	".LT",		LCOND,	C_SCOND_LT,
+	".GT",		LCOND,	C_SCOND_GT,
+	".LE",		LCOND,	C_SCOND_LE,
+	".AL",		LCOND,	C_SCOND_NONE,
 
 	".U",		LS,	C_UBIT,
 	".S",		LS,	C_SBIT,
@@ -505,8 +505,8 @@ outcode(int a, int scond, Addr *g1, int reg, Addr *g2)
 
 	/* hack to make B.NE etc. work: turn it into the corresponding conditional */
 	if(a == AB){
-		a = bcode[scond&0xf];
-		scond = (scond & ~0xf) | Always;
+		a = bcode[(scond^C_SCOND_XOR)&0xf];
+		scond = (scond & ~0xf) | C_SCOND_NONE;
 	}
 
 	if(pass == 1)

src/cmd/5a/y.tab.c

@@ -2028,7 +2028,7 @@ yyreduce:
 		g.offset =
 			(0xe << 24) |		/* opcode */
 			((yyvsp[(1) - (12)].lval) << 20) |		/* MCR/MRC */
-			((yyvsp[(2) - (12)].lval) << 28) |		/* scond */
+			(((yyvsp[(2) - (12)].lval)^C_SCOND_XOR) << 28) |		/* scond */
 			(((yyvsp[(3) - (12)].lval) & 15) << 8) |	/* coprocessor number */
 			(((yyvsp[(5) - (12)].lval) & 7) << 21) |	/* coprocessor operation */
 			(((yyvsp[(7) - (12)].lval) & 15) << 12) |	/* arm register */

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

@@ -321,22 +321,27 @@ enum
 	C_FBIT = 1<<7,	/* psr flags-only */
 	C_UBIT = 1<<7,	/* up bit, unsigned bit */
 
-	C_SCOND_EQ = 0,
-	C_SCOND_NE = 1,
-	C_SCOND_HS = 2,
-	C_SCOND_LO = 3,
-	C_SCOND_MI = 4,
-	C_SCOND_PL = 5,
-	C_SCOND_VS = 6,
-	C_SCOND_VC = 7,
-	C_SCOND_HI = 8,
-	C_SCOND_LS = 9,
-	C_SCOND_GE = 10,
-	C_SCOND_LT = 11,
-	C_SCOND_GT = 12,
-	C_SCOND_LE = 13,
-	C_SCOND_NONE = 14,
-	C_SCOND_NV = 15,
+	// These constants are the ARM condition codes encodings,
+	// XORed with 14 so that C_SCOND_NONE has value 0,
+	// so that a zeroed Prog.scond means "always execute".
+	C_SCOND_XOR = 14,
+
+	C_SCOND_EQ = 0 ^ C_SCOND_XOR,
+	C_SCOND_NE = 1 ^ C_SCOND_XOR,
+	C_SCOND_HS = 2 ^ C_SCOND_XOR,
+	C_SCOND_LO = 3 ^ C_SCOND_XOR,
+	C_SCOND_MI = 4 ^ C_SCOND_XOR,
+	C_SCOND_PL = 5 ^ C_SCOND_XOR,
+	C_SCOND_VS = 6 ^ C_SCOND_XOR,
+	C_SCOND_VC = 7 ^ C_SCOND_XOR,
+	C_SCOND_HI = 8 ^ C_SCOND_XOR,
+	C_SCOND_LS = 9 ^ C_SCOND_XOR,
+	C_SCOND_GE = 10 ^ C_SCOND_XOR,
+	C_SCOND_LT = 11 ^ C_SCOND_XOR,
+	C_SCOND_GT = 12 ^ C_SCOND_XOR,
+	C_SCOND_LE = 13 ^ C_SCOND_XOR,
+	C_SCOND_NONE = 14 ^ C_SCOND_XOR,
+	C_SCOND_NV = 15 ^ C_SCOND_XOR,
 
 	/* D_SHIFT type */
 	SHIFT_LL = 0<<5,

src/liblink/list5.c

@@ -90,7 +90,7 @@ Pconv(Fmt *fp)
 	bigP = p;
 	a = p->as;
 	s = p->scond;
-	strcpy(sc, extra[s & C_SCOND]);
+	strcpy(sc, extra[(s & C_SCOND) ^ C_SCOND_XOR]);
 	if(s & C_SBIT)
 		strcat(sc, ".S");
 	if(s & C_PBIT)