Re: V2 [PATCH] x86: Optimize EVEX vector load/store instructions

["Jan Beulich" <JBeulich@suse.com>]

>>> On 17.03.19 at 21:47, <hjl.tools@gmail.com> wrote:
> --- a/gas/config/tc-i386.c
> +++ b/gas/config/tc-i386.c
> @@ -4075,6 +4075,56 @@ optimize_encoding (void)
>  	    i.types[j].bitfield.ymmword = 0;
>  	  }
>      }
> +  else if ((cpu_arch_flags.bitfield.cpuavx
> +	    || cpu_arch_isa_flags.bitfield.cpuavx)

Once again a questionable condition, as per earlier replies to
other patches of yours.

> +	   && i.vec_encoding != vex_encoding_evex
> +	   && !i.types[0].bitfield.zmmword
> +	   && !i.mask
> +	   && is_evex_encoding (&i.tm)
> +	   && (i.tm.base_opcode == 0x666f
> +	       || (i.tm.base_opcode ^ Opcode_SIMD_IntD) == 0x666f
> +	       || i.tm.base_opcode == 0xf36f
> +	       || (i.tm.base_opcode ^ Opcode_SIMD_IntD) == 0xf36f
> +	       || i.tm.base_opcode == 0xf26f
> +	       || (i.tm.base_opcode ^ Opcode_SIMD_IntD) == 0xf26f)

All three of these can be expressed with just a single comparison,
using & or | instead of ^ and (if necessary) adjusting the literal
value compared against.

> +	   && i.tm.extension_opcode == None)
> +    {
> +      /* Optimize: -O1:
> +	   VOP, one of vmovdqa32, vmovdqa64, vmovdqu8, vmovdqu16,
> +	   vmovdqu32 and vmovdqu64:
> +	     EVEX VOP %xmmM, %xmmN
> +	       -> VEX vmovdqa|vmovdqu %xmmM, %xmmN (M and N < 16)
> +	     EVEX VOP %ymmM, %ymmN
> +	       -> VEX vmovdqa|vmovdqu %ymmM, %ymmN (M and N < 16)
> +	     EVEX VOP %xmmM, mem
> +	       -> VEX vmovdqa|vmovdqu %xmmM, mem (M < 16)
> +	     EVEX VOP %ymmM, mem
> +	       -> VEX vmovdqa|vmovdqu %ymmM, mem (M < 16)
> +	     EVEX VOP mem, %xmmN
> +	       -> VEX mvmovdqa|vmovdquem, %xmmN (N < 16)

There's some confusion on this line.

> +	     EVEX VOP mem, %ymmN
> +	       -> VEX vmovdqa|vmovdqu mem, %ymmN (N < 16)
> +       */

For the variants with a memory operand I doubt the conversion
is always a win, and it may be against the user request in case of
-Os. This is because of the Disp8 scaling the EVEX encoding permits.

> +      if (i.tm.base_opcode == 0xf26f)
> +	i.tm.base_opcode = 0xf36f;
> +      else if ((i.tm.base_opcode ^ Opcode_SIMD_IntD) == 0xf26f)
> +	i.tm.base_opcode = 0xf36f ^ Opcode_SIMD_IntD;

This again can be expressed without "else if()" afaict.

Jan