[PATCH] Simple improvement for predicate computation in if-convert phase.

[Yuri Rumyantsev]

Hi All,

Here is a simple enhancement for predicate computation in if-convert phase:

 We use notion of cd equivalence to get simpler predicate for
     join block, e.g. if join block has 2 predecessors with predicates
     p1 & p2 and p1 & !p2, we'd like to get p1 for it instead of
     p1 & p2 | p1 & !p2.

Bootstrap and regression testing did not show any new failures.

Is it OK for trunk?

gcc/ChangeLog
2014-10-16  Yuri Rumyantsev  <ysrum...@gmail.com>

* tree-if-conv.c (add_to_predicate_list): Check unconditionally
that bb is always executed to early exit. Use predicate of
cd-equivalent block for join blocks if it exists.
(if_convertible_loop_p_1): Recompute POST_DOMINATOR tree.
(tree_if_conversion): Free post-dominance information.

if-conv.patch
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