[PATCH] Simple optimization for MASK_STORE.

[Yuri Rumyantsev]

Hi All,

Here is a patch which gives us significant speed-up on HASWELL for
test containing masked stores. The main goal of that patch is attempt
to avoid HW hazard for maskmove instructions through inserting
additional check on zero mask and putting all masked store statements
into separate block on false edge.All MASK_STORE statements having the
same mask put into one block. Any comments will be appreciate.

ChangeLog:
2015-05-06  Yuri Rumyantsev  <ysrumyan@gmail.com>

* cfgloop.h (has_mask_store): Add new field to struct loop.
* config/i386/i386.c: Include files stringpool.h and tree-ssanames.h.
(ix86_vectorize_zero_vector): New function.
(TARGET_VECTORIZE_ZERO_VECTOR): New target macro
* doc/tm.texi.in: Add @hook TARGET_VECTORIZE_ZERO_VECTOR.
* doc/tm.texi: Updated.
* target.def (zero_vector): New DEFHOOK.
* tree-if-conv.c (predicate_mem_writes): Set has_mask_store for loop.
* tree-vect-stmts.c : Include tree-into-ssa.h.
(optimize_mask_stores): New function.
* tree-vectorizer.c (vectorize_loops): Zero has_mask_store field for
non-vectorized loops and invoke optimize_mask_stores function.

gcc/testsuite/ChangeLog:
* gcc.target/i386/avx2-vect-mask-store-move1.c: New test.
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