[PATCH 3/3][AArch64] Improve zero extend

[Richard Earnshaw (lists)]

On 19/07/16 16:32, Wilco Dijkstra wrote:
> On AArch64 the UXTB and UXTH instructions are aliases of UBFM,
> which does a shift as part of its operation. An AND immediate is a
> simpler operation, and might be faster on some implementations, so it is
> better to emit this this instead of UBFM.
> 
> Benchmarking showed no difference on implementations where UBFM has
> the same performance as AND, and minor speedups across several
> benchmarks on an implementation where UBFM is slower than AND.
> 
> Bootstrapped and tested on aarch64-none-elf.
> 
> 2016-07-19  Kristina Martsenko  <kristina.martsenko@arm.com>
> 2016-07-19  Wilco Dijkstra  <wdijkstr@arm.com>
> 
>         * config/aarch64/aarch64.md
>         (zero_extend<SHORT:mode><GPI:mode>2_aarch64): Change output
>         statement and type.
>         (<optab>qihi2_aarch64): Likewise, and split into two.
>         (extendqihi2_aarch64): New.
>         (zero_extendqihi2_aarch64): New.
>         * config/aarch64/iterators.md (ldrxt): Remove.
>         * config/aarch64/aarch64.c (aarch64_rtx_costs): Change cost of
>         uxtb/uxth.

This looks sensible to me, but please wait 24 hours before committing,
just to allow the other folk with different implementations to comment
if they wish.

R.

> ---
> 
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index c7249e8e98905bea4879bb2e2ee81d51a1004faa..e98e41521bfa8f807248b0147843de9e1f3447e3 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -6886,8 +6886,8 @@ cost_plus:
>  	    }
>  	  else
>  	    {
> -	      /* UXTB/UXTH.  */
> -	      *cost += extra_cost->alu.extend;
> +	      /* We generate an AND instead of UXTB/UXTH.  */
> +	      *cost += extra_cost->alu.logical;
>  	    }
>  	}
>        return false;
> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
> index 64f9ca1c4d1bec64cef769c9dbef9e4b5b00ba9e..5e8b1a815515eabc7e69c75574c2c300f50a6fe4 100644
> --- a/gcc/config/aarch64/aarch64.md
> +++ b/gcc/config/aarch64/aarch64.md
> @@ -1580,10 +1580,10 @@
>          (zero_extend:GPI (match_operand:SHORT 1 "nonimmediate_operand" "r,m,m")))]
>    ""
>    "@
> -   uxt<SHORT:size>\t%<GPI:w>0, %w1
> +   and\t%<GPI:w>0, %<GPI:w>1, <SHORT:short_mask>
>     ldr<SHORT:size>\t%w0, %1
>     ldr\t%<SHORT:size>0, %1"
> -  [(set_attr "type" "extend,load1,load1")]
> +  [(set_attr "type" "logic_imm,load1,load1")]
>  )
>  
>  (define_expand "<optab>qihi2"
> @@ -1592,16 +1592,26 @@
>    ""
>  )
>  
> -(define_insn "*<optab>qihi2_aarch64"
> +(define_insn "*extendqihi2_aarch64"
>    [(set (match_operand:HI 0 "register_operand" "=r,r")
> -        (ANY_EXTEND:HI (match_operand:QI 1 "nonimmediate_operand" "r,m")))]
> +	(sign_extend:HI (match_operand:QI 1 "nonimmediate_operand" "r,m")))]
>    ""
>    "@
> -   <su>xtb\t%w0, %w1
> -   <ldrxt>b\t%w0, %1"
> +   sxtb\t%w0, %w1
> +   ldrsb\t%w0, %1"
>    [(set_attr "type" "extend,load1")]
>  )
>  
> +(define_insn "*zero_extendqihi2_aarch64"
> +  [(set (match_operand:HI 0 "register_operand" "=r,r")
> +	(zero_extend:HI (match_operand:QI 1 "nonimmediate_operand" "r,m")))]
> +  ""
> +  "@
> +   and\t%w0, %w1, 255
> +   ldrb\t%w0, %1"
> +  [(set_attr "type" "logic_imm,load1")]
> +)
> +
>  ;; -------------------------------------------------------------------
>  ;; Simple arithmetic
>  ;; -------------------------------------------------------------------
> diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
> index e8fbb1281dec2e8f37f58ef2ced792dd62e3b5aa..ef48ffda6f98a2d4aa29daaca206fef2bafcda48 100644
> --- a/gcc/config/aarch64/iterators.md
> +++ b/gcc/config/aarch64/iterators.md
> @@ -888,9 +888,6 @@
>  ;; Similar, but when not(op)
>  (define_code_attr nlogical [(and "bic") (ior "orn") (xor "eon")])
>  
> -;; Sign- or zero-extending load
> -(define_code_attr ldrxt [(sign_extend "ldrs") (zero_extend "ldr")])
> -
>  ;; Sign- or zero-extending data-op
>  (define_code_attr su [(sign_extend "s") (zero_extend "u")
>  		      (sign_extract "s") (zero_extract "u")
>