Ensure floating point comparisons with NaN are unordered (always return FALSE except for !=).
On ARM this is just a matter of using the right condition codes (cc in PSR has different
meaning when set from the FPSCR after a floating point comparison).

Reference: /n/sources/patch/applied/5c-nan-cmp
Date: Fri Sep 20 11:00:09 CES 2013
Signed-off-by: miller@hamnavoe.com

--- /sys/src/cmd/5c/cgen.c	Fri Sep 20 10:45:58 2013
+++ /sys/src/cmd/5c/cgen.c	Fri Sep 20 10:45:54 2013
@@ -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);
@@ -800,14 +800,14 @@
 			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;
 		}
 		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);
 
--- /sys/src/cmd/5c/gc.h	Fri Sep 20 10:46:03 2013
+++ /sys/src/cmd/5c/gc.h	Fri Sep 20 10:46:00 2013
@@ -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;
--- /sys/src/cmd/5c/txt.c	Fri Sep 20 10:46:09 2013
+++ /sys/src/cmd/5c/txt.c	Fri Sep 20 10:46:05 2013
@@ -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;