PATCH: simplify_and_const_int - disable call to force_to_mode

[Toshi Morita <moritat at hsa dot hitachi dot com>]

This problem exists in both gcc-2.95.3-test3 and the gcc-3.0 branch.

If this is acceptable, please apply to both branches.

Mon Feb 26 10:37:43 PST 2001  Toshiyasu Morita  (tm2@best.com)

        * combine.c (simplify_and_const_int): Disable call to
force_to_mode.

*** combine.c.bak       Thu Feb 22 20:49:53 2001
--- combine.c   Mon Feb 26 10:36:09 2001
***************
*** 7317,7325 ****
--- 7317,7347 ----
    int width = GET_MODE_BITSIZE (mode);
    int i;

+ #if 0
+   /* This optimization is invalid because force_to_mode is designed to
+      propogate the bitmask for a mode into the subexpressions of an
expression.
+      It does NOT always return an expression truncated to an arbitrary
bitmask.
+
+      Basically, when this code is enabled, simplify_and_const_it
simplifies:
+
+      (set (reg/v:SI 57) (const_int 0))
+
+      (and:SI (plus:SI (reg/v:SI 57)
+              (const_int 23 [0x17]))
+          (const_int 60 [0x3c]))
+
+      to:
+
+      (const_int 23 [0x17])
+
+      because force_to_mode is forced to widen the mask because the
+      low-order bits affect the result.
+   */
+
    /* Simplify VAROP knowing that we will be only looking at some of the
       bits in it.  */
    varop = force_to_mode (varop, mode, constop, NULL_RTX, 0);
+ #endif

    /* If VAROP is a CLOBBER, we will fail so return it; if it is a
       CONST_INT, we are done.  */