[PATCH, 2/2] Extended if-conversion for loops marked with pragma omp simd.

[Yuri Rumyantsev <ysrumyan at gmail dot com>]

Richard,

Here is second part of patch which includes
1. One particular phi node recognition  - if phi function has more
than 2 arguments but it has only two really different arguments and
one argument has the only occurrence. This is important for
conditional scalar reduction conversion, e.g. for such test-case;
     if (a[i] != 0 && b[i] != 0)  n++;
2. New sub-pass which repairs bool pattern candidates with multiple
uses - such situation occurres if the same predicate (not simple
compare) is used for phi node conversion and load/store mask. If for
some var participating in tree traversal its def stmt has multiple
uses we create copy of this definition with unique left hand side and
change one use of original vat to newly created one. We repeat this
process until all multiple uses will be deleted.
3. Another sub-pass which  delete redundant predicate computations
which are dead locally, i.e. local dead code elimination. Note that
such dead code can prevent loop vectorization.

Changelog:

2014-10-13  Yuri Rumyantsev  <ysrumyan@gmail.com>

* tree-if-conv.c (cgraph.h): Add include file to issue error message.
(phi_has_two_different_args): New function.
(is_cond_scalar_reduction): Add argument EXTENDED to choose access
to phi arguments. Invoke phi_has_two_different_args to get phi
arguments iff EXTENDED is true. Change check stmt-block is predecessor
of phi-block since phi may haave more than two arguments.
(convert_scalar_cond_reduction): Add argument BEFORE to insert
statement before/after gsi point.
(predicate_scalar_phi): Add argument false to call of
is_cond_scalar_reduction. Add argument true to call of
convert_scalar_cond_reduction.
(predicate_arbitrary_scalar_phi): Change result of function to tree
representing rhs of new phi replacement stmt.
(predicate_extended_scalar_phi): New function.
(predicate_all_scalar_phis): Invoke predicate_extended_scalar_phi
instead of predicate_arbitrary_scalar_phi.
(ifcvt_split_def_stmt): New function.
(ifcvt_walk_pattern_tree): New function.
(stmt_is_root_of_bool_pattern): New function.
(ifcvt_repair_bool_pattern): New function.
(ifcvt_local_dce): New function.
(tree_if_conversion): Invoke ifcvt_local_dce and
ifcvt_repair_bool_pattern under FLAG_FORCE_VECTORIZE.

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