Re: [PATCH][AArch64] Improve immediate expansion [PR106583]

[Richard Sandiford <richard.sandiford@arm.com>]

Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> Improve immediate expansion of immediates which can be created from a
> bitmask immediate and 2 MOVKs.  This reduces the number of 4-instruction
> immediates in SPECINT/FP by 10-15%.
>
> Passes regress, OK for commit?
>
> gcc/ChangeLog:
>
>         PR target/106583
>         * config/aarch64/aarch64.cc (aarch64_internal_mov_immediate)
>         Add support for a bitmask immediate with 2 MOVKs.
>
> gcc/testsuite:
>         PR target/106583
>         * gcc.target/aarch64/pr106583.c: Add new test.

Nice.

Did you consider handling the case where the movks aren't for
consecutive bitranges?  E.g. the patch handles:

  0x12345678aaaaaaaa

and:

  0x1234cccccccc5678

but it looks like it would be fairly easy to extend it to:

  0x1234cccc5678cccc

too.

Also, could you commonise:

	  val2 = val & ~mask;
	  if (val2 != val && aarch64_bitmask_imm (val2, mode))
	    break;
	  val2 = val | mask;
	  if (val2 != val && aarch64_bitmask_imm (val2, mode))
	    break;
	  val2 = val2 & ~mask;
	  val2 = val2 | (((val2 >> 32) | (val2 << 32)) & mask);
	  if (val2 != val && aarch64_bitmask_imm (val2, mode))
	    break;

?  It's subtle enough that IMO it'd be better not to cut-&-paste it.

Thanks,
Richard

> ---
>
> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> index 926e81f028c82aac9a5fecc18f921f84399c24ae..1601d11710cb6132c80a77bb4fe2f8429519aa5a 100644
> --- a/gcc/config/aarch64/aarch64.cc
> +++ b/gcc/config/aarch64/aarch64.cc
> @@ -5568,7 +5568,7 @@ aarch64_internal_mov_immediate (rtx dest, rtx imm, bool generate,
>    one_match = ((~val & mask) == 0) + ((~val & (mask << 16)) == 0) +
>      ((~val & (mask << 32)) == 0) + ((~val & (mask << 48)) == 0);
>
> -  if (zero_match != 2 && one_match != 2)
> +  if (zero_match < 2 && one_match < 2)
>      {
>        /* Try emitting a bitmask immediate with a movk replacing 16 bits.
>          For a 64-bit bitmask try whether changing 16 bits to all ones or
> @@ -5600,6 +5600,43 @@ aarch64_internal_mov_immediate (rtx dest, rtx imm, bool generate,
>         }
>      }
>
> +  /* Try a bitmask plus 2 movk to generate the immediate in 3 instructions.  */
> +  if (zero_match + one_match == 0)
> +    {
> +      mask = 0xffffffff;
> +
> +      for (i = 0; i < 64; i += 16)
> +       {
> +         val2 = val & ~mask;
> +         if (aarch64_bitmask_imm (val2, mode))
> +           break;
> +         val2 = val | mask;
> +         if (aarch64_bitmask_imm (val2, mode))
> +           break;
> +         val2 = val2 & ~mask;
> +         val2 = val2 | (((val2 >> 32) | (val2 << 32)) & mask);
> +         if (aarch64_bitmask_imm (val2, mode))
> +           break;
> +
> +         mask = (mask << 16) | (mask >> 48);
> +       }
> +
> +      if (i != 64)
> +       {
> +         if (generate)
> +           {
> +             emit_insn (gen_rtx_SET (dest, GEN_INT (val2)));
> +             emit_insn (gen_insv_immdi (dest, GEN_INT (i),
> +                                        GEN_INT ((val >> i) & 0xffff)));
> +             i = (i + 16) & 63;
> +             emit_insn (gen_insv_immdi (dest, GEN_INT (i),
> +                                        GEN_INT ((val >> i) & 0xffff)));
> +           }
> +
> +         return 3;
> +       }
> +    }
> +
>    /* Generate 2-4 instructions, skipping 16 bits of all zeroes or ones which
>       are emitted by the initial mov.  If one_match > zero_match, skip set bits,
>       otherwise skip zero bits.  */
> diff --git a/gcc/testsuite/gcc.target/aarch64/pr106583.c b/gcc/testsuite/gcc.target/aarch64/pr106583.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..f0a027a0950e506d4ddaacce5e151f57070948dc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/pr106583.c
> @@ -0,0 +1,30 @@
> +/* { dg-do assemble } */
> +/* { dg-options "-O2 --save-temps" } */
> +
> +long f1 (void)
> +{
> +  return 0x7efefefefefefeff;
> +}
> +
> +long f2 (void)
> +{
> +  return 0x12345678aaaaaaaa;
> +}
> +
> +long f3 (void)
> +{
> +  return 0x1234cccccccc5678;
> +}
> +
> +long f4 (void)
> +{
> +  return 0x7777123456787777;
> +}
> +
> +long f5 (void)
> +{
> +  return 0x5555555512345678;
> +}
> +
> +/* { dg-final { scan-assembler-times {\tmovk\t} 10 } } */
> +/* { dg-final { scan-assembler-times {\tmov\t} 5 } } */