see 5c-nan-cmp on sources by richard miller announced on 9fans with:

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).

the readme says:
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/atom/patch/applied2013/x5c-nan-cmp
Date: Fri Sep 20 14:31:36 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/5c/txt.c	Fri Sep 20 14:29:44 2013
+++ /sys/src/cmd/5c/txt.c	Fri Sep 20 14:29:45 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;
--- /sys/src/cmd/5c/gc.h	Fri Sep 20 14:29:45 2013
+++ /sys/src/cmd/5c/gc.h	Fri Sep 20 14:29:46 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;
@@ -125,7 +126,7 @@
 };
 #define	R	((Reg*)0)
 
-#define	NRGN	600
+#define	NRGN	1000		/* was 600; raised for paranoia.c */
 struct	Rgn
 {
 	Reg*	enter;
--- /sys/src/cmd/5c/cgen.c	Fri Sep 20 14:29:47 2013
+++ /sys/src/cmd/5c/cgen.c	Fri Sep 20 14:29:48 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);