[v4,4/4] tdesc: handle arbitrary strings in tdesc_register_in_reggroup_p

diff --git a/gdb/NEWS b/gdb/NEWS
index 44f481d1f5..c861853798 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,10 @@ 
 
 *** Changes since GDB 8.0
 
+* GDB now supports dynamically creating arbitrary register groups specified
+  in XML target descriptions.  This allows for finer grain grouping of
+  registers on systems with a large amount of registers.
+
 * The 'ptype' command now accepts a '/o' flag, which prints the
   offsets and sizes of fields in a struct, like the pahole(1) tool.
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a16e79bc2a..f8ecf216b4 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -41761,10 +41761,13 @@  architecture's normal floating point format) of the correct size for
 @var{bitsize}.  The default is @code{int}.
 
 @item group
-The register group to which this register belongs.  It must
-be either @code{general}, @code{float}, or @code{vector}.  If no
-@var{group} is specified, @value{GDBN} will not display the register
-in @code{info registers}.
+The register group to which this register belongs.  It can be one of the
+standard register groups @code{general}, @code{float}, @code{vector} or an
+arbitrary string.  Group names should be limited to alphanumeric characters.
+If a group name is made up of multiple words the words may be separated by
+hyphens; e.g.@: @code{special-group} or @code{ultra-special-group}.  If no
+@var{group} is specified, @value{GDBN} will not display the register in
+@code{info registers}.
 
 @end table
 
diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c
index 88ac55f404..349cebb51b 100644
--- a/gdb/target-descriptions.c
+++ b/gdb/target-descriptions.c
@@ -111,12 +111,11 @@  struct tdesc_reg : tdesc_element
   int save_restore;
 
   /* The name of the register group containing this register, or empty
-     if the group should be automatically determined from the
-     register's type.  If this is "general", "float", or "vector", the
-     corresponding "info" command should display this register's
-     value.  It can be an arbitrary string, but should be limited to
-     alphanumeric characters and internal hyphens.  Currently other
-     strings are ignored (treated as empty).  */
+     if the group should be automatically determined from the register's
+     type.  This is traditionally "general", "float", "vector" but can
+     also be an arbitrary string.  If defined the corresponding "info"
+     command should display this register's value.  The string should be
+     limited to alphanumeric characters and internal hyphens.  */
   std::string group;
 
   /* The size of the register, in bits.  */
@@ -1279,17 +1278,13 @@  tdesc_remote_register_number (struct gdbarch *gdbarch, int regno)
 }
 
 /* Check whether REGNUM is a member of REGGROUP.  Registers from the
-   target description may be classified as general, float, or vector.
-   Unlike a gdbarch register_reggroup_p method, this function will
-   return -1 if it does not know; the caller should handle registers
-   with no specified group.
-
-   Arbitrary strings (other than "general", "float", and "vector")
-   from the description are not used; they cause the register to be
-   displayed in "info all-registers" but excluded from "info
-   registers" et al.  The names of containing features are also not
-   used.  This might be extended to display registers in some more
-   useful groupings.
+   target description may be classified as general, float, vector or other
+   register groups registered with reggroup_add().  Unlike a gdbarch
+   register_reggroup_p method, this function will return -1 if it does not
+   know; the caller should handle registers with no specified group.
+
+   The names of containing features are not used.  This might be extended
+   to display registers in some more useful groupings.
 
    The save-restore flag is also implemented here.  */
 
@@ -1299,26 +1294,9 @@  tdesc_register_in_reggroup_p (struct gdbarch *gdbarch, int regno,
 {
   struct tdesc_reg *reg = tdesc_find_register (gdbarch, regno);
 
-  if (reg != NULL && !reg->group.empty ())
-    {
-      int general_p = 0, float_p = 0, vector_p = 0;
-
-      if (reg->group == "general")
-	general_p = 1;
-      else if (reg->group == "float")
-	float_p = 1;
-      else if (reg->group == "vector")
-	vector_p = 1;
-
-      if (reggroup == float_reggroup)
-	return float_p;
-
-      if (reggroup == vector_reggroup)
-	return vector_p;
-
-      if (reggroup == general_reggroup)
-	return general_p;
-    }
+  if (reg != NULL && !reg->group.empty ()
+      && (reg->group == reggroup_name (reggroup)))
+	return 1;
 
   if (reg != NULL
       && (reggroup == save_reggroup || reggroup == restore_reggroup))
@@ -1421,6 +1399,12 @@  tdesc_use_registers (struct gdbarch *gdbarch,
 	void **slot = htab_find_slot (reg_hash, reg.get (), INSERT);
 
 	*slot = reg.get ();
+	/* Add reggroup if its new.  */
+	if (!reg->group.empty ())
+	  if (reggroup_find (gdbarch, reg->group.c_str ()) == NULL)
+	    reggroup_add (gdbarch, reggroup_gdbarch_new (gdbarch,
+							 reg->group.c_str (),
+							 USER_REGGROUP));
       }
 
   /* Remove any registers which were assigned numbers by the
diff --git a/gdb/testsuite/gdb.xml/extra-regs.xml b/gdb/testsuite/gdb.xml/extra-regs.xml
index 997d6598e5..302e64ce7d 100644
--- a/gdb/testsuite/gdb.xml/extra-regs.xml
+++ b/gdb/testsuite/gdb.xml/extra-regs.xml
@@ -53,5 +53,6 @@ 
     <reg name="bitfields" bitsize="64" type="struct2"/>
     <reg name="flags" bitsize="32" type="flags"/>
     <reg name="mixed_flags" bitsize="32" type="mixed_flags"/>
+    <reg name="groupreg" bitsize="32" type="uint32" group="foo"/>
   </feature>
 </target>
diff --git a/gdb/testsuite/gdb.xml/tdesc-regs.exp b/gdb/testsuite/gdb.xml/tdesc-regs.exp
index d62ed9841b..e8b7fd506b 100644
--- a/gdb/testsuite/gdb.xml/tdesc-regs.exp
+++ b/gdb/testsuite/gdb.xml/tdesc-regs.exp
@@ -190,6 +190,9 @@  gdb_test "ptype \$flags" \
     "type = flag flags {\r\n *bool X @0;\r\n *uint32_t Y @2;\r\n}"
 gdb_test "ptype \$mixed_flags" \
     "type = flag mixed_flags {\r\n *bool A @0;\r\n *uint32_t B @1-3;\r\n *bool C @4;\r\n *uint32_t D @5;\r\n *uint32_t @6-7;\r\n *enum {yes = 1, no = 0, maybe = 2, so} Z @8-9;\r\n}"
+# Reggroups should have at least general and the extra foo group
+gdb_test "maintenance print reggroups" \
+    " Group\[ \t\]+Type\[ \t\]+\r\n.* general\[ \t\]+user\[ \t\]+\r\n.* foo\[ \t\]+user\[ \t\]+"
 
 load_description "core-only.xml" "" "test-regs.xml"
 # The extra register from the previous description should be gone.