target-arm/translate-a64.c: Correct unallocated checks for ldst_excl

The checks for the unallocated encodings in the ldst_excl group
(exclusives and load-acquire/store-release) were not correct. This
error meant that in turn we ended up with code attempting to handle
the non-existent case of "non-exclusive load-acquire/store-release
pair". Delete that broken and now unreachable code.
Reported-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NLaurent Desnogues <laurent.desnogues@gmail.com>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: NSergey Fedorov <serge.fdrv@gmail.com>

target-arm/translate-a64.c

@@ -1816,9 +1816,6 @@ static void gen_store_exclusive(DisasContext *s, int rd, int rt, int rt2,
  *  o2: 0 -> exclusive, 1 -> not
  *  o1: 0 -> single register, 1 -> register pair
  *  o0: 1 -> load-acquire/store-release, 0 -> not
- *
- *  o0 == 0 AND o2 == 1 is un-allocated
- *  o1 == 1 is un-allocated except for 32 and 64 bit sizes
  */
 static void disas_ldst_excl(DisasContext *s, uint32_t insn)
 {
@@ -1833,7 +1830,8 @@ static void disas_ldst_excl(DisasContext *s, uint32_t insn)
     int size = extract32(insn, 30, 2);
     TCGv_i64 tcg_addr;
 
-    if ((!is_excl && !is_lasr) ||
+    if ((!is_excl && !is_pair && !is_lasr) ||
+        (!is_excl && is_pair) ||
         (is_pair && size < 2)) {
         unallocated_encoding(s);
         return;
@@ -1862,15 +1860,6 @@ static void disas_ldst_excl(DisasContext *s, uint32_t insn)
         } else {
             do_gpr_ld(s, tcg_rt, tcg_addr, size, false, false);
         }
-        if (is_pair) {
-            TCGv_i64 tcg_rt2 = cpu_reg(s, rt);
-            tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
-            if (is_store) {
-                do_gpr_st(s, tcg_rt2, tcg_addr, size);
-            } else {
-                do_gpr_ld(s, tcg_rt2, tcg_addr, size, false, false);
-            }
-        }
     }
 }