[AArch64] Remove AARCH64_EXTRA_TUNE_RECIP_SQRT from Cortex-A57 tuning

[James Greenhalgh <james.greenhalgh@arm.com>]

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Hi,

I've seen a couple of large performance issues caused by expanding
the high-precision reciprocal square root for Cortex-A57, so I'd like
to turn it off by default.

This is good for art (~2%) from Spec2000, bad (~3.5%) for fma3d from
Spec2000, good (~5.5%) for gromcas from Spec2006, and very good (>10%) for
some private microbenchmark kernels which stress the divide/sqrt/multiply
units. It therefore seems to me to be the correct choice to make across
a number of workloads.

Bootstrapped and tested on aarch64-none-linux-gnu with no issues.

OK?

Thanks,
James

---
2015-12-11  James Greenhalgh  <james.greenhalgh@arm.com>

	* config/aarch64/aarch64.c (cortexa57_tunings): Remove
	AARCH64_EXTRA_TUNE_RECIP_SQRT.


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diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 1d5d898..999c9fc 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -484,8 +484,7 @@ static const struct tune_params cortexa57_tunings =
   0,	/* max_case_values.  */
   0,	/* cache_line_size.  */
   tune_params::AUTOPREFETCHER_WEAK,	/* autoprefetcher_model.  */
-  (AARCH64_EXTRA_TUNE_RENAME_FMA_REGS
-   | AARCH64_EXTRA_TUNE_RECIP_SQRT)	/* tune_flags.  */
+  (AARCH64_EXTRA_TUNE_RENAME_FMA_REGS)	/* tune_flags.  */
 };
 
 static const struct tune_params cortexa72_tunings =