Re: [PATCH][AArch64] Model Cortex-A53 load forwarding

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 05/04/17 13:29, Wilco Dijkstra wrote:
> Code scheduling for Cortex-A53 isn't as good as it could be.  It turns out
> code runs faster overall if we place loads and stores with a dependency
> closer together.  To achieve this effect, this patch adds a bypass between
> cortex_a53_load1 and cortex_a53_load*/cortex_a53_store* if the result of an
> earlier load is used in an address calculation.  This significantly improved
> benchmark scores in a proprietary benchmark suite.
> 
> Passes AArch64 bootstrap and regress. OK for stage 1?
> 

What about an ARM bootstrap?  OK if that also passes.

R.

> ChangeLog:
> 2017-04-05  Wilco Dijkstra  <wdijkstr@arm.com>
> 
> 	* config/arm/aarch-common.c (arm_early_load_addr_dep_ptr):
> 	New function.
> 	(arm_early_store_addr_dep_ptr): Likewise.
> 	* config/arm/aarch-common-protos.h
> 	(arm_early_load_addr_dep_ptr): Add prototype.
> 	(arm_early_store_addr_dep_ptr): Likewise.
> 	* config/arm/cortex-a53.md: Add new bypasses.
> ---
> 
> diff --git a/gcc/config/arm/aarch-common-protos.h b/gcc/config/arm/aarch-common-protos.h
> index 8e9fb7a895b0a4aaf1585eb3368443899b061c9b..5298172e6b6930a110388a40a7533ff208a87095 100644
> --- a/gcc/config/arm/aarch-common-protos.h
> +++ b/gcc/config/arm/aarch-common-protos.h
> @@ -30,7 +30,9 @@ extern bool aarch_rev16_p (rtx);
>  extern bool aarch_rev16_shleft_mask_imm_p (rtx, machine_mode);
>  extern bool aarch_rev16_shright_mask_imm_p (rtx, machine_mode);
>  extern int arm_early_load_addr_dep (rtx, rtx);
> +extern int arm_early_load_addr_dep_ptr (rtx, rtx);
>  extern int arm_early_store_addr_dep (rtx, rtx);
> +extern int arm_early_store_addr_dep_ptr (rtx, rtx);
>  extern int arm_mac_accumulator_is_mul_result (rtx, rtx);
>  extern int arm_mac_accumulator_is_result (rtx, rtx);
>  extern int arm_no_early_alu_shift_dep (rtx, rtx);
> diff --git a/gcc/config/arm/aarch-common.c b/gcc/config/arm/aarch-common.c
> index dd37be0291a633f606d95ec8acacc598435828b3..74b80b272550028919c4274387944867ffed43d1 100644
> --- a/gcc/config/arm/aarch-common.c
> +++ b/gcc/config/arm/aarch-common.c
> @@ -241,6 +241,24 @@ arm_early_load_addr_dep (rtx producer, rtx consumer)
>    return reg_overlap_mentioned_p (value, addr);
>  }
>  
> +/* Return nonzero if the CONSUMER instruction (a load) does need
> +   a Pmode PRODUCER's value to calculate the address.  */
> +
> +int
> +arm_early_load_addr_dep_ptr (rtx producer, rtx consumer)
> +{
> +  rtx value = arm_find_sub_rtx_with_code (PATTERN (producer), SET, false);
> +  rtx addr = arm_find_sub_rtx_with_code (PATTERN (consumer), SET, false);
> +
> +  if (!value || !addr || !MEM_P (SET_SRC (value)))
> +    return 0;
> +
> +  value = SET_DEST (value);
> +  addr = SET_SRC (addr);
> +
> +  return GET_MODE (value) == Pmode && reg_overlap_mentioned_p (value, addr);
> +}
> +
>  /* Return nonzero if the CONSUMER instruction (an ALU op) does not
>     have an early register shift value or amount dependency on the
>     result of PRODUCER.  */
> @@ -336,6 +354,24 @@ arm_early_store_addr_dep (rtx producer, rtx consumer)
>    return !arm_no_early_store_addr_dep (producer, consumer);
>  }
>  
> +/* Return nonzero if the CONSUMER instruction (a store) does need
> +   a Pmode PRODUCER's value to calculate the address.  */
> +
> +int
> +arm_early_store_addr_dep_ptr (rtx producer, rtx consumer)
> +{
> +  rtx value = arm_find_sub_rtx_with_code (PATTERN (producer), SET, false);
> +  rtx addr = arm_find_sub_rtx_with_code (PATTERN (consumer), SET, false);
> +
> +  if (!value || !addr || !MEM_P (SET_SRC (value)))
> +    return 0;
> +
> +  value = SET_DEST (value);
> +  addr = SET_DEST (addr);
> +
> +  return GET_MODE (value) == Pmode && reg_overlap_mentioned_p (value, addr);
> +}
> +
>  /* Return non-zero iff the consumer (a multiply-accumulate or a
>     multiple-subtract instruction) has an accumulator dependency on the
>     result of the producer and no other dependency on that result.  It
> diff --git a/gcc/config/arm/cortex-a53.md b/gcc/config/arm/cortex-a53.md
> index b367ad403a4a641da34521c17669027b87092737..f8225f33c7a06485147b30fe2633309ac252d0c7 100644
> --- a/gcc/config/arm/cortex-a53.md
> +++ b/gcc/config/arm/cortex-a53.md
> @@ -246,6 +246,16 @@
>  		 "cortex_a53_store*"
>  		 "arm_no_early_store_addr_dep")
>  
> +;; Model a bypass for load to load/store address.
> +
> +(define_bypass 3 "cortex_a53_load1"
> +		 "cortex_a53_load*"
> +		 "arm_early_load_addr_dep_ptr")
> +
> +(define_bypass 3 "cortex_a53_load1"
> +		 "cortex_a53_store*"
> +		 "arm_early_store_addr_dep_ptr")
> +
>  ;; Model a GP->FP register move as similar to stores.
>  
>  (define_bypass 0 "cortex_a53_alu*,cortex_a53_shift*"
>