Jmk told me of this bug.

Reference: /n/patches.lsub.org/patch/comp6cbug
Date: Wed Jul  4 17:04:35 CES 2012
Signed-off-by: paurea@lsub.org

--- /sys/src/cmd/6c/cgen.c	Thu Apr 12 12:25:19 2012
+++ /sys/src/cmd/6c/cgen.c	Wed Jul  4 17:03:00 2012
@@ -574,7 +574,7 @@
 				reglcgen(&nod, l, Z);
 			else
 				nod = *l;
-			if(o != OASMUL && o != OASADD) {
+			if(o != OASMUL && o != OASADD || !typefd[l->type->etype]) {
 				regalloc(&nod2, r, Z);
 				gmove(&nod, &nod2);
 				gopcode(o, r->type, &nod1, &nod2);