Use post-dom info to update if/switch predicate

Use post-dom info to update if/switch predicate

2019-09-19  Feng Xue  <fxue@os.amperecomputing.com>

        * ipa-fnsummary.c (set_cond_stmt_execution_predicate): Do not compute
        trivial predicate for condition branch.
        (set_switch_stmt_execution_predicate): Do not compute trivial predicate
        for switch case.
        (compute_bb_predicates): Update predicate based on post-dominating
        relationship.
        (analyze_function_body): Calculate post-dominating information.

2019-09-19  Feng Xue  <fxue@os.amperecomputing.com>

        * gcc.dg/ipa/pr91089.c: Add a new function and pattern.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@275963 138bc75d-0d04-0410-961f-82ee72b054a4