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5c: apply richard millers 5c-nan-cmp patch (from sources)

On ARM, it turns out that comparisons with NaN can be made to do the
right thing with no code penalty, by a more careful selection of
condition code values in the subsequent conditional branch.  The
meaning of the CC bits in the PSR is subtly different when they've
been copied from the floating point status register.

Suggested patch is 5c-nan-cmp (works on both vfp and emulated arm7500).

--- a/sys/src/cmd/5c/cgen.c

+++ b/sys/src/cmd/5c/cgen.c

@@ -701,7 +701,7 @@

 		if(true)

 			o = comrel[relindex(o)];

 		if(typefd[n->type->etype]) {

-			gopcode(o, nodfconst(0), &nod, Z);

+			gopcode(true ? o | BTRUE : o, nodfconst(0), &nod, Z);

 		} else

 			gopcode(o, nodconst(0), &nod, Z);

 		regfree(&nod);

@@ -800,7 +800,7 @@

 			regalloc(&nod, r, nn);

 			cgenrel(r, &nod, 1);

 			o = invrel[relindex(o)];

-			gopcode(o, l, &nod, Z);

+			gopcode(true ? o | BTRUE : o, l, &nod, Z);

 			regfree(&nod);

 			goto com;

 		}

@@ -807,7 +807,7 @@

 		if(sconst(r)) {

 			regalloc(&nod, l, nn);

 			cgenrel(l, &nod, 1);

-			gopcode(o, r, &nod, Z);

+			gopcode(true ? o | BTRUE : o, r, &nod, Z);

 			regfree(&nod);

 			goto com;

 		}

@@ -822,7 +822,7 @@

 			regalloc(&nod1, l, Z);

 			cgenrel(l, &nod1, 1);

 		}

-		gopcode(o, &nod, &nod1, Z);

+		gopcode(true ? o | BTRUE : o, &nod, &nod1, Z);

 		regfree(&nod);

 		regfree(&nod1);

--- a/sys/src/cmd/5c/gc.h

+++ b/sys/src/cmd/5c/gc.h

@@ -14,6 +14,7 @@

 #define	SZ_VLONG	8

 #define	SZ_DOUBLE	8

 #define	FNX		100

+#define BTRUE		0x1000

 typedef	struct	Adr	Adr;

 typedef	struct	Prog	Prog;

--- a/sys/src/cmd/5c/txt.c

+++ b/sys/src/cmd/5c/txt.c

@@ -929,12 +929,14 @@

 void

 gopcode(int o, Node *f1, Node *f2, Node *t)

 {

-	int a, et;

+	int a, et, true;

 	Adr ta;

 	et = TLONG;

 	if(f1 != Z && f1->type != T)

 		et = f1->type->etype;

+	true = o & BTRUE;

+	o &= ~BTRUE;

 	a = AGOK;

 	switch(o) {

 	case OAS:

@@ -1076,15 +1078,24 @@

 			break;

 		case OLT:

 			a = ABLT;

+			/* ensure NaN comparison is always false */

+			if(typefd[et] && !true)

+				a = ABMI;

 			break;

 		case OLE:

 			a = ABLE;

+			if(typefd[et] && !true)

+				a = ABLS;

 			break;

 		case OGE:

 			a = ABGE;

+			if(typefd[et] && true)

+				a = ABPL;

 			break;

 		case OGT:

 			a = ABGT;

+			if(typefd[et] && true)

+				a = ABHI;

 			break;

 		case OLO:

 			a = ABLO;

-- 

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