Re: [PATCH 1/3] [AARCH64] Add macro fusion support for cmp/b.X for ThunderX

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

Hi Andrew,

On 14/11/14 00:56, Andrew Pinski wrote:
> In ThunderX, any 1 cycle arthemantic instruction that produces the flags
> register, will be fused with a branch.  This patch depends on
> https://gcc.gnu.org/ml/gcc-patches/2014-11/msg01508.html.
> Note I know bit 1 is going is already going to be used and that is why I
> proposed this being bit 2.
>
> Build and tested for aarch64-elf with no regressions.
>
> ChangeLog:
> * config/aarch64/aarch64.c (AARCH64_FUSE_CMP_BRANCH): New define.
> (thunderx_tunings): Add AARCH64_FUSE_CMP_BRANCH to fuseable_ops.
> (aarch_macro_fusion_pair_p): Handle AARCH64_FUSE_CMP_BRANCH.
> ---
>   gcc/config/aarch64/aarch64.c |   15 ++++++++++++++-
>   1 files changed, 14 insertions(+), 1 deletions(-)
>
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index a258f40..5216ac0 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -304,6 +304,7 @@ static const struct cpu_vector_cost cortexa57_vector_cost =
>   
>   #define AARCH64_FUSE_NOTHING	(0)
>   #define AARCH64_FUSE_MOV_MOVK	(1 << 0)
> +#define AARCH64_FUSE_CMP_BRANCH	(1 << 2)
>   
>   #if HAVE_DESIGNATED_INITIALIZERS && GCC_VERSION >= 2007
>   __extension__
> @@ -349,7 +350,7 @@ static const struct tune_params thunderx_tunings =
>     &generic_vector_cost,
>     NAMED_PARAM (memmov_cost, 6),
>     NAMED_PARAM (issue_rate, 2),
> -  NAMED_PARAM (fuseable_ops, AARCH64_FUSE_NOTHING)
> +  NAMED_PARAM (fuseable_ops, AARCH64_FUSE_CMP_BRANCH)
>   };
>   
>   /* A processor implementing AArch64.  */
> @@ -10036,6 +10037,18 @@ aarch_macro_fusion_pair_p (rtx_insn *prev, rtx_insn *curr)
>           }
>       }
>   
> +  if ((aarch64_tune_params->fuseable_ops & AARCH64_FUSE_CMP_BRANCH)
> +      && any_condjump_p (curr))
> +    {
> +      /* FIXME: this misses some which is considered simple arthematic
> +         instructions for ThunderX.  Simple shifts are missed here.  */
s/is/are

> +      if (get_attr_type (prev) == TYPE_ALUS_SREG
> +          || get_attr_type (prev) == TYPE_ALUS_IMM
> +          || get_attr_type (prev) == TYPE_LOGICS_REG
> +          || get_attr_type (prev) == TYPE_LOGICS_IMM)
> +	return true;

IIRC the get_attr_* functions can call recog_memoized on prev which can 
potentially change
the recog_data for the insn, sometimes resulting in corruption. Is this 
definitely safe to do?

Kyrill

> +    }
> +
>     return false;
>   }
>