Hi,
This patch rebases the floating-point cost table for Cortex-A57 to be
relative to the cost of a floating-point move. This in response to this
feedback from Richard Sandiford [2] on Ramana's patch to calls.c [1] from
2014:
I think this is really a bug in the backend. The backend is assigning a
cost of COSTS_N_INSNS (3) to a floating-point constant not because the
constant itself is expensive -- it's actually as cheap as a register
in this context -- but because the backend considers floating-point
moves to be 3 times more expensive than cheap integer moves.
The argument is that a move in mode X should be treated with cost
COSTS_N_INSNS (1), and other instructions should have a cost relative to
that move. For example, in this patch we say that instructions building a
floating-point constant are the same cost as a floating-point register to
register move. Fixing this fixes the issue Ramana was seeing, in a way
consistent with what other back-ends do.
This patch gives a small improvement to Spec2000FP on a Cortex-A57
platform.
Bootstrapped on aarch64-none-linux-gnu with no issues.
OK?
Thanks,
James
---
2016-06-03 James Greenhalgh <james.greenha...@arm.com>
* config/arm/aarch-cost-tables.h (cortexa57_extra_costs): Make FP
costs relative to the cost of a register move.
[1] https://gcc.gnu.org/ml/gcc-patches/2014-10/msg00136.html
[2] https://gcc.gnu.org/ml/gcc-patches/2014-10/msg00391.html
diff --git a/gcc/config/arm/aarch-cost-tables.h b/gcc/config/arm/aarch-cost-tables.h
index c971b30..5f42253 100644
--- a/gcc/config/arm/aarch-cost-tables.h
+++ b/gcc/config/arm/aarch-cost-tables.h
@@ -294,35 +294,35 @@ const struct cpu_cost_table cortexa57_extra_costs =
{
/* FP SFmode */
{
- COSTS_N_INSNS (17), /* div. */
- COSTS_N_INSNS (5), /* mult. */
- COSTS_N_INSNS (9), /* mult_addsub. */
- COSTS_N_INSNS (9), /* fma. */
- COSTS_N_INSNS (4), /* addsub. */
- COSTS_N_INSNS (2), /* fpconst. */
- COSTS_N_INSNS (2), /* neg. */
- COSTS_N_INSNS (2), /* compare. */
- COSTS_N_INSNS (4), /* widen. */
- COSTS_N_INSNS (4), /* narrow. */
- COSTS_N_INSNS (4), /* toint. */
- COSTS_N_INSNS (4), /* fromint. */
- COSTS_N_INSNS (4) /* roundint. */
+ COSTS_N_INSNS (6), /* div. */
+ COSTS_N_INSNS (1), /* mult. */
+ COSTS_N_INSNS (2), /* mult_addsub. */
+ COSTS_N_INSNS (2), /* fma. */
+ COSTS_N_INSNS (1), /* addsub. */
+ 0, /* fpconst. */
+ 0, /* neg. */
+ 0, /* compare. */
+ COSTS_N_INSNS (1), /* widen. */
+ COSTS_N_INSNS (1), /* narrow. */
+ COSTS_N_INSNS (1), /* toint. */
+ COSTS_N_INSNS (1), /* fromint. */
+ COSTS_N_INSNS (1) /* roundint. */
},
/* FP DFmode */
{
- COSTS_N_INSNS (31), /* div. */
- COSTS_N_INSNS (5), /* mult. */
- COSTS_N_INSNS (9), /* mult_addsub. */
- COSTS_N_INSNS (9), /* fma. */
- COSTS_N_INSNS (4), /* addsub. */
- COSTS_N_INSNS (2), /* fpconst. */
- COSTS_N_INSNS (2), /* neg. */
- COSTS_N_INSNS (2), /* compare. */
- COSTS_N_INSNS (4), /* widen. */
- COSTS_N_INSNS (4), /* narrow. */
- COSTS_N_INSNS (4), /* toint. */
- COSTS_N_INSNS (4), /* fromint. */
- COSTS_N_INSNS (4) /* roundint. */
+ COSTS_N_INSNS (11), /* div. */
+ COSTS_N_INSNS (1), /* mult. */
+ COSTS_N_INSNS (2), /* mult_addsub. */
+ COSTS_N_INSNS (2), /* fma. */
+ COSTS_N_INSNS (1), /* addsub. */
+ 0, /* fpconst. */
+ 0, /* neg. */
+ 0, /* compare. */
+ COSTS_N_INSNS (1), /* widen. */
+ COSTS_N_INSNS (1), /* narrow. */
+ COSTS_N_INSNS (1), /* toint. */
+ COSTS_N_INSNS (1), /* fromint. */
+ COSTS_N_INSNS (1) /* roundint. */
}
},
/* Vector */
