RISC-V: Clarify the behavior of .option rvc or norvc.

Add/Remove the rvc extension to/from the riscv_subsets once the
.option rvc/norvc is set.  So that we don't need to always check
the riscv_opts.rvc in the riscv_subset_supports, just call the
riscv_lookup_subset to search the subset list is enough.

Besides, we will need to dump the instructions according to the
elf architecture attributes.  That means the dis-assembler needs
to parse the architecture string from the elf attribute before
dumping any instructions, and also needs to recognized the
INSN_CLASS* classes from riscv_opcodes.  Therefore, I suppose
some functions will need to be moved from gas/config/tc-riscv.c
to bfd/elfxx-riscv.c, including riscv_multi_subset_supports and
riscv_subset_supports.  This is one of the reasons why we need
this patch.

This patch passes the gcc/binutils regressions of rv32emc-elf,
rv32i-elf, rv64gc-elf and rv64gc-linux toolchains.

bfd/
	* elfxx-riscv.c (riscv_remove_subset): Remove the extension
	from the subset list.
	(riscv_update_subset): Add/Remove an extension to/from the
	subset list.  This is used for the .option rvc or norvc.
	* elfxx-riscv.h: Added the extern bool riscv_update_subset.
gas/
	* config/tc-riscv.c (riscv_set_options): Removed the unused
	rve flag.
	(riscv_opts): Likewise.
	(riscv_set_rve): Removed.
	(riscv_subset_supports): Removed the riscv_opts.rvc check.
	(riscv_set_arch): Don't need to call riscv_set_rve.
	(reg_lookup_internal): Call riscv_subset_supports to check
	whether the rve is supported.
	(s_riscv_option): Add/Remove the rvc extension to/from the
	subset list once the .option rvc/norvc is set.

2 files changed, 68 insertions, 0 deletions

diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
index cdb4fa0..65bb1ca 100644
--- a/bfd/elfxx-riscv.c
+++ b/bfd/elfxx-riscv.c
@@ -2030,3 +2030,68 @@ riscv_arch_str (unsigned xlen, const riscv_subset_list_t *subset)
 
   return attr_str;
 }
+
+/* Remove the SUBSET from the subset list.  */
+
+static void
+riscv_remove_subset (riscv_subset_list_t *subset_list,
+		     const char *subset)
+{
+  riscv_subset_t *current = subset_list->head;
+  riscv_subset_t *pre = NULL;
+  for (; current != NULL; pre = current, current = current->next)
+    {
+      if (strcmp (current->name, subset) == 0)
+	{
+	  if (pre == NULL)
+	    subset_list->head = current->next;
+	  else
+	    pre->next = current->next;
+	  if (current->next == NULL)
+	    subset_list->tail = pre;
+	  free ((void *) current->name);
+	  free (current);
+	  break;
+	}
+    }
+}
+
+/* Add/Remove an extension to/from the subset list.  This is used for
+   the .option rvc or norvc.  */
+
+bool
+riscv_update_subset (riscv_parse_subset_t *rps,
+		     const char *subset,
+		     bool removed)
+{
+  if (strlen (subset) == 0
+      || (strlen (subset) == 1
+	  && riscv_ext_order[(*subset - 'a')] == 0)
+      || (strlen (subset) > 1
+	  && rps->check_unknown_prefixed_ext
+	  && !riscv_recognized_prefixed_ext (subset)))
+    {
+      rps->error_handler
+	(_("riscv_update_subset: unknown ISA extension `%s'"), subset);
+      return false;
+    }
+
+  if (removed)
+    {
+      if (strcmp (subset, "i") == 0)
+	{
+	  rps->error_handler
+	    (_("riscv_update_subset: cannot remove extension i from "
+	       "the subset list"));
+	  return false;
+	}
+      riscv_remove_subset (rps->subset_list, subset);
+    }
+  else
+    riscv_parse_add_subset (rps, subset,
+			    RISCV_UNKNOWN_VERSION,
+			    RISCV_UNKNOWN_VERSION, true);
+
+  riscv_parse_add_implicit_subsets (rps);
+  return riscv_parse_check_conflicts (rps);
+}
diff --git a/bfd/elfxx-riscv.h b/bfd/elfxx-riscv.h
index 3af8fd9..17620fd 100644
--- a/bfd/elfxx-riscv.h
+++ b/bfd/elfxx-riscv.h
@@ -92,6 +92,9 @@ riscv_estimate_digit (unsigned);
 extern int
 riscv_compare_subsets (const char *, const char *);
 
+extern bool
+riscv_update_subset (riscv_parse_subset_t *, const char *, bool);
+
 extern void
 bfd_elf32_riscv_set_data_segment_info (struct bfd_link_info *, int *);
 extern void