Fix PR77673: bswap loads passed end of object

Fix PR77673: bswap loads passed end of object

2016-11-25  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/
    PR tree-optimization/77673
    * tree-ssa-math-opts.c (struct symbolic_number): Add new src field.
    (init_symbolic_number): Initialize src field from src parameter.
    (perform_symbolic_merge): Select most dominated statement as the
    source statement.  Set src field of resulting n structure from the
    input src with the lowest address.
    (find_bswap_or_nop): Rename source_stmt into ins_stmt.
    (bswap_replace): Rename src_stmt into ins_stmt.  Initially get source
    of load from src field rather than insertion statement.  Cancel
    optimization if statement analyzed is not dominated by the insertion
    statement.
    (pass_optimize_bswap::execute): Rename src_stmt to ins_stmt.  Compute
    dominance information.

    gcc/testsuite/
    PR tree-optimization/77673
    * gcc.dg/pr77673.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@242869 138bc75d-0d04-0410-961f-82ee72b054a4