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Re: [PATCH][ARM] Implement vectorizer cost hooks


On 05/02/13 18:18, Christophe Lyon wrote:
Hi,

Following the discussion about "disable peeling" [1] a few weeks ago,
it turned out that the vectorizer cost model needed some
implementation for ARM.

The attached patch implements arm_builtin_vectorization_cost and
arm_add_stmt_cost, providing default costs when aligned and unaligned
loads/stores have the same cost (=1). init_cost and finish_cost still
use the default implementation (I noticed that x86 has chosen to
duplicate the default implementation without changing it, why?)

Benchmarking shows very little variation, expect a noticeable +1.6% on coremark.

If this is OK, we can then discuss how to disable peeling completely
when aligned and unaligned accesses have the same cost (and thus where
peeling is a loss of performance). I think adding a new hook is
necessary, since target descriptions may use different models for
these costs (eg x86 makes no difference between unaligned loads and
unaligned stores).

Thanks,

Christophe.

[1] http://gcc.gnu.org/ml/gcc/2012-12/msg00036.html

2013-02-05 Christophe Lyon <christophe.lyon@linaro.org>

         * config/arm/arm.c (arm_builtin_vectorization_cost)
         (arm_add_stmt_cost): New functions.
         (TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST)
         (TARGET_VECTORIZE_ADD_STMT_COST): Define.
         (struct processor_costs): New struct type.
         (default_arm_cost): New struct of type processor_costs.=


Christophe,


Thanks for the patch. This is mostly OK, but please can you make the following changes.

+struct processor_costs {

Please name this something like cpu_vec_costs. It's not the only cost table in the back-end.

+struct processor_costs default_arm_cost = { /* arm generic costs. */

Similarly, use something like default_arm_vec_cost.

+const struct processor_costs *arm_cost = &default_arm_cost;

And here. But better still, link this through the current_tune table rather than introducing a new global.

Finally,

@@ -27256,4 +27272,130 @@ arm_validize_comparison (rtx *comparison, rtx * op1, rtx * op2)

}

+/* Vectorizer cost model implementation. */


Please put the patch in a more suitable location rather than just dumping it at the end of the file. There are already numerous functions related to costs that are mostly grouped together. I suggest this goes near the rtx_costs code.


R.



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