target-m68k: increment/decrement with SP

On 680x0 family only.

Address Register indirect With postincrement:

When using the stack pointer (A7) with byte size data, the register
is incremented by two.

Address Register indirect With predecrement:

When using the stack pointer (A7) with byte size data, the register
is decremented by two.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Thomas Huth <huth@tuxfamily.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Message-Id: <1484332593-16782-6-git-send-email-laurent@vivier.eu>

target/m68k/translate.c

@@ -725,7 +725,12 @@ static TCGv gen_lea_mode(CPUM68KState *env, DisasContext *s,
         }
         reg = get_areg(s, reg0);
         tmp = tcg_temp_new();
-        tcg_gen_subi_i32(tmp, reg, opsize_bytes(opsize));
+        if (reg0 == 7 && opsize == OS_BYTE &&
+            m68k_feature(s->env, M68K_FEATURE_M68000)) {
+            tcg_gen_subi_i32(tmp, reg, 2);
+        } else {
+            tcg_gen_subi_i32(tmp, reg, opsize_bytes(opsize));
+        }
         return tmp;
     case 5: /* Indirect displacement.  */
         reg = get_areg(s, reg0);
@@ -801,7 +806,12 @@ static TCGv gen_ea_mode(CPUM68KState *env, DisasContext *s, int mode, int reg0,
         result = gen_ldst(s, opsize, reg, val, what);
         if (what == EA_STORE || !addrp) {
             TCGv tmp = tcg_temp_new();
-            tcg_gen_addi_i32(tmp, reg, opsize_bytes(opsize));
+            if (reg0 == 7 && opsize == OS_BYTE &&
+                m68k_feature(s->env, M68K_FEATURE_M68000)) {
+                tcg_gen_addi_i32(tmp, reg, 2);
+            } else {
+                tcg_gen_addi_i32(tmp, reg, opsize_bytes(opsize));
+            }
             delay_set_areg(s, reg0, tmp, true);
         }
         return result;