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.greenha...@arm.com>
* config/aarch64/aarch64.c (cortexa57_tunings): Remove
AARCH64_EXTRA_TUNE_RECIP_SQRT.
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 =
