RISC-V: Fallback on faster hash table

Although it does not have a problem on current GNU Binutils implementation,
if the custom vendor implements an instruction which spans across multiple
major opcodes, the faster hash table breaks.

In this case, this commit enables the fallback mode to disable all
optimizations except filtering macros out.

opcodes/ChangeLog:

	* riscv-dis.c (is_riscv_hash_fallback) New.
	(build_riscv_opcodes_hash_table): If an instruction spans across
	multiple major opcodes, enable fallback mode and disable sorting.
	(riscv_disassemble_insn): If the fallback mode is enabled, scan
	through all instructions instead of scanning only instruction
	entries matching the hash value.

opcodes/riscv-dis.c

@@ -260,6 +260,9 @@ update_riscv_dis_xlen (struct disassemble_info *info)
 static const struct riscv_opcode **riscv_hash[OP_HASH_LEN + 1];
 static const struct riscv_opcode **riscv_opcodes_sorted;
 
+/* Whether the fallback should be used.  */
+static bool is_riscv_hash_fallback = false;
+
 /* Compare two riscv_opcode* objects to sort by hash index.  */
 
 static int
@@ -290,15 +293,25 @@ build_riscv_opcodes_hash_table (void)
 
   /* Sort riscv_opcodes entry pointers (except macros).  */
   for (op = riscv_opcodes; op->name; op++)
-    if (op->pinfo != INSN_MACRO)
+    {
+      if (op->pinfo == INSN_MACRO)
+	continue;
       len++;
+      if (is_riscv_hash_fallback)
+	continue;
+      if (OP_HASH_IDX (op->match) < OP_MASK_OP2
+	      ? (op->mask & OP_MASK_OP2) != OP_MASK_OP2
+	      : (op->mask & OP_MASK_OP)  != OP_MASK_OP)
+	is_riscv_hash_fallback = true;
+    }
   riscv_opcodes_sorted = xcalloc (len, sizeof (struct riscv_opcode *));
   pop_end = riscv_opcodes_sorted;
   for (op = riscv_opcodes; op->name; op++)
     if (op->pinfo != INSN_MACRO)
       *pop_end++ = op;
-  qsort (riscv_opcodes_sorted, len, sizeof (struct riscv_opcode *),
-	 compare_opcodes);
+  if (!is_riscv_hash_fallback)
+    qsort (riscv_opcodes_sorted, len, sizeof (struct riscv_opcode *),
+	   compare_opcodes);
 
   /* Initialize faster hash table.  */
   pop = riscv_opcodes_sorted;
@@ -813,8 +826,16 @@ riscv_disassemble_insn (bfd_vma memaddr, insn_t word, disassemble_info *info)
   info->target2 = 0;
 
   matched_op = NULL;
-  pop     = riscv_hash[OP_HASH_IDX (word)];
-  pop_end = riscv_hash[OP_HASH_IDX (word) + 1];
+  if (!is_riscv_hash_fallback)
+    {
+      pop     = riscv_hash[OP_HASH_IDX (word)];
+      pop_end = riscv_hash[OP_HASH_IDX (word) + 1];
+    }
+  else
+    {
+      pop     = riscv_hash[0];
+      pop_end = riscv_hash[OP_HASH_LEN];
+    }
   for (; pop != pop_end; pop++)
     {
       op = *pop;