[Committed] Delete tree_fold_gcd

[Roger Sayle]

As I first commented a long while back, the only use of the function
tree_fold_gcd in the tree is in tree-data-ref.c's tree_fold_divides_p to
test whether one integer constant is a multiple of another.
http://gcc.gnu.org/ml/gcc-patches/2005-12/msg01699.html

It turns out that using Greatest-Common-Divisor to test this via the
comparison "gcd(a,b) == a" is a particularly inefficient implementation. 
Instead the patch below follows the idiom used in fold-const.c's
multiple_of_p routine which is to call int_const_binop with the tree code
TRUNC_MOD_EXPR and test whether the return value is zero. It would be nice
not to create the tree node for the result, but this already significantly
better then the current implementation which creates numerous tree nodes.

The following patch has been tested on x86_64-unknown-linux-gnu with a
full "make bootstrap", all default languages, and regression tested with a
top-level "make -k check" with no new failures.

Committed to mainline as revision 121253.


2007-01-27  Roger Sayle  <roger@eyesopen.com>

        * tree.c (tree_fold_gcd): Delete.
        * tree.h (tree_fold_gcd): Remove prototype.
        * tree-data-ref.c (tree_fold_divides_p): Don't use tree_fold_gcd to
        test whether one constant integer is a multiple of another.  Instead
        call int_const_binop with TRUNC_MOD_EXPR and test for a zero result.
        * fold-const.c (multiple_of_p):  We've determined both TOP and
        BOTTOM are integer constants so we can call int_const_binop directly
        instead of the more generic const_binop.

Roger
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