[patch] vectorizer cost-model: fixes and powerpc testcases

[Dorit Nuzman <DORIT at il dot ibm dot com>]

Hi,

This patch adds powerpc tests for the vectorizer cost model, and fixes a
few issues in the cost model that I discovered while playing with these
tests:

1- The main cost model function is called twice - once during analysis, and
once again in vect_do_peeling_for_loop_bound (to get the threshold that
controls whether the vector loop will be executed). This is wrong because
each time the cost model is called it adds the estimated costs to the
STMT_VINFO_*_OF_LOOP_COST fields, so we get wrong inflated costs when we
call it the second time. We really want to call it only once, and record
the estimated threshold somewhere. This patch adds a new field for that:
LOOP_VINFO_COST_MODEL_MIN_ITERS.

2- The cost model always adds loop-versioning costs because it checks
whether LOOP_VINFO_MAY_MISALIGN_STMTS is not NULL, instead of checking that
it is not empty (i.e. using VEC_length).

3- The calculation of peel_iters_prologue is wrong: it was set to
LOOP_PEELING_FOR_ALIGNMENT which is the misalignment of the data-reference
in bytes. Instead it should be set to:
      min (niters, vs - mis)
...where 'vs' is the vector size in number of elements, and 'mis' is the
misalignment in number of elements.

4- Adding the branch-costs due to prologue/epilogue creation is done before
peel_iters_prologue/epilogue are accurately computed (so we may not add
epilogue branch-costs although later on we determine that an epilogue will
be generated). This patch moves it to after we compute
peel_iters_prologue/epilogue.

5- Turns out we're not considering the cost of creating a vector from a
scalar when we have operations that use constant or invariant values. This
patch adds a new cost - TARG_SCALAR_TO_VEC_COST, and also passes the
def-type "dt" (which says whether a use is constant/invariant/defined in
the loop, etc) to vect_model_simple_cost and vect_model_store_cost so that
these functions could add the TARG_SCALAR_TO_VEC_COST when appropriate.

6- We now always print that "vectorization may not be profitable". This is
changed to be printed only when the cost model returned a non-zero
threshold, and the number of iterations is unknown.

Harsha, I had to change the expected dg-final check in one of the i386
tests due to the changes above. There maybe some things need to be modified
for the x86_64 tests too - could you take a look at that?

Bootstrapped on i386-linux and powerpc-linux
Tested on the vectorizer testcases on powerpc-linux
Passed full regression testing on i386-linux.

This patch is just bug fixes, but I'm not sure if it counts as a
"regression fix" and can be committed to mainline during the current
freeze?

thanks,
dorit

ChangeLogs:

        * tree-vectorizer.c (new_loop_vec_info): Initialize
        LOOP_VINFO_COST_MODEL_MIN_ITERS.
        * tree-vectorizer.h (_loop_vec_info): Added new filed
        min_profitable_iters.
        (LOOP_VINFO_COST_MODEL_MIN_ITERS): New access macro to above new
field.
        (TARG_SCALAR_TO_VEC_COST): Define cost of scalar to vector
operation.
        * tree-vect-analyze.c (vect_analyze_operations): Set
        LOOP_VINFO_COST_MODEL_MIN_ITERS.
        * tree-vect-transform.c (vect_estimate_min_profitable_iters): Use
        VEC_length to determine if there are any
LOOP_VINFO_MAY_MISALIGN_STMTS.
        Fix calculation of peel_iters_prologue. Move consideration of
epilogue
        and prologue cost to after they are computed.
        (vect_model_induction_cost): Use TARG_SCALAR_TO_VEC_COST instead of
        TARG_VEC_STMT_COST.
        (vect_model_simple_cost): Takes additional argument dt. Consider
cost
        of creating vectors from scalars according to dt.
        (vect_model_store_cost): Likewise.
        (vectorizable_call): Use dt array instead of scalar dt. Call
        vect_model_simple_cost with additional argument dt.
        (vectorizable_assignment): Likewise.
        (vectorizable_operation): Likewise.
        (vectorizable_type_demotion): Likewise.
        (vectorizable_type_promotion): Likewise.
        (vectorizable_store): Use dt array instead of scalar dt. Call
        vect_model_store_cost with additional argument dt.
        (vect_do_peeling_for_loop_bound): Don't call
        vect_estimate_min_profitable_iters. Instead, lookup
        LOOP_VINFO_COST_MODEL_MIN_ITERS. Don't always print
        "may not be profitable".

        * gcc.dg/vect/costmodel/ppc: New directory.
        * gcc.dg/vect/costmodel/ppc/ppc-costmodel-vect.exp: New.
        * gcc.dg/vect/costmodel/ppc/costmodel-fast-math-vect-pr29925.c: New
test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-31a.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-31b.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-31c.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-31d.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-33.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-76a.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-76b.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-76c.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-68a.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-68b.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-68c.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-68d.c: New test.
        * gcc.dg/vect/costmodel/ppc/costmodel-vect-reduc-1char.c: New test.
        * gcc.dg/vect/costmodel/i386/costmodel-vect-68.c: Now vectorized.

(See attached file: costmodelfixes.june16.txt)

Attachment: costmodelfixes.june16.txt
Description: Text document