[PATCH, ARM] Suppress Redundant Flag Setting for Cortex-A15

Ramana Radhakrishnan ramana.gcc@googlemail.com
Tue Jan 28 12:10:00 GMT 2014


On Fri, Jan 24, 2014 at 5:16 PM, Ian Bolton <ian.bolton@arm.com> wrote:
> Hi there!
>
> An existing optimisation for Thumb-2 converts t32 encodings to
> t16 encodings to reduce codesize, at the expense of causing
> redundant flag setting for ADD, AND, etc.  This redundant flag
> setting can have negative performance impact on cortex-a15.
>
> This patch introduces two new tuning options so that the conversion
> from t32 to t16, which takes place in thumb2_reorg, can be suppressed
> for cortex-a15.
>
> To maintain some of the original benefit (reduced codesize), the
> suppression is only done where the enclosing basic block is deemed
> worthy of optimising for speed.
>
> This tested with no regressions and performance has improved for
> the workloads tested on cortex-a15.  (It might be beneficial to
> other processors too, but that has not been investigated yet.)
>
> OK for stage 1?

This is OK for stage1.

Ramana

>
> Cheers,
> Ian
>
>
> 2014-01-24  Ian Bolton  <ian.bolton@arm.com>
>
> gcc/
>         * config/arm/arm-protos.h (tune_params): New struct members.
>         * config/arm/arm.c: Initialise tune_params per processor.
>         (thumb2_reorg): Suppress conversion from t32 to t16 when
>         optimizing for speed, based on new tune_params.



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