http://bugs.gentoo.org/257054

MIPS: smarter code for constant addresses

http://gcc.gnu.org/ml/gcc/2008-11/msg00231.html

--- a/gcc/config/mips/mips.c	2009-03-02 21:26:22.000000000 +0100
+++ b/gcc/config/mips/mips.c	2009-08-16 11:56:08.000000000 +0200
@@ -2795,7 +2795,7 @@ bool
 mips_legitimize_address (rtx *xloc, enum machine_mode mode)
 {
   rtx base, addr;
-  HOST_WIDE_INT offset;
+  HOST_WIDE_INT intval, high, offset;
 
   if (mips_tls_symbol_p (*xloc))
     {
@@ -2820,6 +2820,33 @@ mips_legitimize_address (rtx *xloc, enum
       *xloc = mips_force_address (addr, mode);
       return true;
     }
+
+  /* Handle references to constant addresses by loading the high part
+     into a register and using an offset for the low part.  */
+  if (GET_CODE (base) == CONST_INT)
+    {
+      intval = INTVAL (base);
+      high = trunc_int_for_mode (CONST_HIGH_PART (intval), Pmode);
+      offset = CONST_LOW_PART (intval);
+     /* Ignore cases in which a positive address would be accessed by a
+       negative offset from a negative address.  The required wraparound
+       does not occur for 32-bit addresses on 64-bit targets, and it is
+       very unlikely that such an access would occur in real code anyway.
+
+       If the low offset is not legitimate for MODE, prefer to load
+       the constant normally, instead of using mips_force_address on
+       the legitimized address.  The latter option would cause us to
+       use (D)ADDIU unconditionally, but LUI/ORI is more efficient
+       than LUI/ADDIU on some targets.  */
+     if ((intval < 0 || high > 0)
+        && mips_valid_offset_p (GEN_INT (offset), mode))
+      {
+        base = mips_force_temporary (NULL, GEN_INT (high));
+        *xloc = plus_constant (base, offset);
+        return true;
+      }
+   }
+
   return false;
 }