final.c (alter_subreg): Allow the target to hook by-mode subreg hard register number changes.

* final.c (alter_subreg): Allow the target to hook by-mode subreg
hard register number changes.

From-SVN: r18946

gcc/ChangeLog

@@ -5,6 +5,8 @@ Thu Apr  2 01:01:34 1998  Richard Henderson  <rth@cygnus.com>
 
 	* emit-rtl.c (gen_lowpart_common): Skip count by HARD_REGNO_NREGS.
 	(gen_highpart): Likewise.
+	* final.c (alter_subreg): Allow the target to hook by-mode subreg
+	hard register number changes.
 	
 Wed Apr  1 22:26:22 1998  Jeffrey A Law  (law@cygnus.com)
 

gcc/final.c

@@ -2891,9 +2891,20 @@ alter_subreg (x)
 
   if (GET_CODE (y) == REG)
     {
-      /* If the containing reg really gets a hard reg, so do we.  */
+      /* If the word size is larger than the size of this register,
+	 adjust the register number to compensate.  */
+      /* ??? Note that this just catches stragglers created by/for
+	 integrate.  It would be better if we either caught these
+	 earlier, or kept _all_ subregs until now and eliminate
+	 gen_lowpart and friends.  */
+
       PUT_CODE (x, REG);
+#ifdef ALTER_HARD_SUBREG
+      REGNO (x) = ALTER_HARD_SUBREG(GET_MODE (x), SUBREG_WORD (x),
+				    GET_MODE (y), REGNO (y));
+#else
       REGNO (x) = REGNO (y) + SUBREG_WORD (x);
+#endif
     }
   else if (GET_CODE (y) == MEM)
     {

gcc/tm.texi

@@ -1403,6 +1403,17 @@ definition of this macro is
     / UNITS_PER_WORD))
 @end smallexample
 
+@findex ALTER_HARD_SUBREG
+@item ALTER_HARD_SUBREG (@var{tgt_mode}, @var{word}, @var{src_mode}, @var{regno})
+A C expression that returns an adjusted hard register number for 
+
+@smallexample
+(subreg:@var{tgt_mode} (reg:@var{src_mode} @var{regno}) @var{word})
+@end smallexample
+
+This may be needed if the target machine has mixed sized big-endian
+registers, like Sparc v9.
+
 @findex HARD_REGNO_MODE_OK
 @item HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
 A C expression that is nonzero if it is permissible to store a value