[PATCH] rx: allow cmpstrnsi len to be zero

The SCMPU instruction doesn't change the C and Z flags when the
incoming length is zero, which means the insn will produce a
value based upon the existing flag values.

As a quick kludge, adjust these flags to ensure a zero result in this
case.

gcc/
	* config/rx/rx.md (rx_cmpstrn): Correctly handle len=0 case.

Author: keith-packard

gcc/config/rx/rx.md

@@ -2590,7 +2590,9 @@
    (clobber (reg:SI 3))
    (clobber (reg:CC CC_REG))]
   "rx_allow_string_insns"
-  "scmpu		; Perform the string comparison
+  "setpsw  z		; Set flags in case len is zero
+   setpsw  c
+   scmpu		; Perform the string comparison
    mov     #-1, %0      ; Set up -1 result (which cannot be created
                         ; by the SC insn)
    bnc	   ?+		; If Carry is not set skip over