rtlanal.c (subreg_get_info): Exit early for simple and common cases.

gcc/
2015-01-25  Alan Hayward  <alan.hayward@arm.com>

	* rtlanal.c (subreg_get_info): Exit early for simple and common
	cases.

From-SVN: r219957

gcc/ChangeLog

+2015-01-21  Alan Hayward  <alan.hayward@arm.com>
+
+	* rtlanal.c (subreg_get_info): Exit early for simple and common
+	cases.
+
 2015-01-21  Richard Henderson  <rth@redhat.com>
 
 	PR target/64669

gcc/rtlanal.c

@@ -3440,6 +3440,22 @@ subreg_get_info (unsigned int xregno, machine_mode xmode,
 	  info->offset = offset / regsize_xmode;
 	  return;
 	}
+      /* Quick exit for the simple and common case of extracting whole
+	 subregisters from a multiregister value.  */
+      /* ??? It would be better to integrate this into the code below,
+	 if we can generalize the concept enough and figure out how
+	 odd-sized modes can coexist with the other weird cases we support.  */
+      if (!rknown
+	  && WORDS_BIG_ENDIAN == REG_WORDS_BIG_ENDIAN
+	  && regsize_xmode == regsize_ymode
+	  && (offset % regsize_ymode) == 0)
+	{
+	  info->representable_p = true;
+	  info->nregs = nregs_ymode;
+	  info->offset = offset / regsize_ymode;
+	  gcc_assert (info->offset + info->nregs <= nregs_xmode);
+	  return;
+	}
     }
 
   /* Lowpart subregs are otherwise valid.  */