In theory this should never happen, as all such instructions
are illegal.  This is checked in e.g. gen_lea_mode and
gen_ea_mode_fp but not here.  In case something higher up
isn't checking modes properly, return NULL_QREG.  This will
result in an illegal instruction exception being raised.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/m68k/translate.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target/m68k/translate.c b/target/m68k/translate.c
index 3055d2d246..7a87811427 100644
--- a/target/m68k/translate.c
+++ b/target/m68k/translate.c
@@ -898,6 +898,10 @@ static TCGv gen_ea_mode(CPUM68KState *env, DisasContext *s, int mode, int reg0,
         case 3: /* pc index+displacement.  */
             goto do_indirect;
         case 4: /* Immediate.  */
+            /* Should never be used for an output or RMW input. */
+            if (what == EA_STORE || addrp) {
+                return NULL_QREG;
+            }
             /* Sign extend values for consistency.  */
             switch (opsize) {
             case OS_BYTE:
-- 
2.34.1