[PATCH, 4.8] Backport alias patches to 4.8 branch

[Uros Bizjak <ubizjak at gmail dot com>]

Hello!

I would like to port following patches to 4.8 branch:

2014-11-05  Uros Bizjak  <ubizjak@gmail.com>

    Backport from mainline
     2015-01-22 Wei Mi <wmi@google.com>

    PR rtl-optimization/64557
    * dse.c (record_store): Call get_addr for mem_addr.
    (check_mem_read_rtx): Likewise.

    Backport from mainline
    2014-10-20  Uros Bizjak  <ubizjak@gmail.com>

    * varasm.c (const_alias_set): Remove.
    (init_varasm_once): Remove initialization of const_alias_set.
    (build_constant_desc): Do not set alias set to const_alias_set.

    Backport from mainline
    2014-10-14  Uros Bizjak  <ubizjak@gmail.com>

    PR rtl-optimization/63475
    * alias.c (true_dependence_1): Always use get_addr to extract
    true address operands from x_addr and mem_addr.  Use extracted
    address operands to check for references with alignment ANDs.
    Use extracted address operands with find_base_term and
    base_alias_check. For noncanonicalized operands call canon_rtx with
    extracted address operand.
    (write_dependence_1): Ditto.
    (may_alias_p): Ditto.  Remove unused calls to canon_rtx.

    Backport from mainline
    2014-10-10  Uros Bizjak  <ubizjak@gmail.com>

    PR rtl-optimization/63483
    * alias.c (true_dependence_1): Do not exit early for MEM_READONLY_P
    references when alignment ANDs are involved.
    (write_dependence_p): Ditto.
    (may_alias_p): Ditto.

    Backport from mainline
    2013-03-26  Richard Biener  <rguenther@suse.de>

    * alias.c (find_base_term): Avoid redundant and not used recursion.
    (base_alias_check): Get the initial base term from the caller.
    (true_dependence_1): Compute and pass base terms to base_alias_check.
    (write_dependence_p): Likewise.
    (may_alias_p): Likewise.

Patches were bootstrapped and regression tested together with
bootstrap fixing patch [1] on alpha-linux-gnu and x86_64-linux-gnu
{,-m32}. These patches fix the same libgfortran failures as on
mainline and 4.9 (all these patches are already present or backported
to 4.9 branch).

The results for alpha-linux-gnu are at [2]

[1] https://gcc.gnu.org/ml/gcc-patches/2015-02/msg01127.html
[2] https://gcc.gnu.org/ml/gcc-testresults/2015-02/msg02244.html

OK for 4.8 branch?

Uros.

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