Kyrylo Tkachov via Gcc-patches <[email protected]> writes:
> Hi all,
>
> This patch implements RTL constant-folding for the SS_TRUNCATE and
> US_TRUNCATE codes.
> The semantics are a clamping operation on the argument with the min and max
> of the narrow mode,
> followed by a truncation. The signedness of the clamp and the min/max extrema
> is derived from
> the signedness of the saturating operation.
>
> We have a number of instructions in aarch64 that use SS_TRUNCATE and
> US_TRUNCATE to represent
> their operations and we have pretty thorough runtime tests in
> gcc.target/aarch64/advsimd-intrinsics/vqmovn*.c.
> With this patch the instructions are folded away at optimisation levels and
> the correctness checks still
> pass.
>
> Bootstrapped and tested on aarch64-none-linux-gnu and aarch64_be-none-elf.
> Ok for trunk?
>
> Thanks,
> Kyrill
>
> gcc/ChangeLog:
>
> * simplify-rtx.cc (simplify_const_unary_operation):
> Handle US_TRUNCATE, SS_TRUNCATE.
>
> diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> index
> 276be67aa67247dd46361ab9badc46ab089d6df0..5983a06e5a8ca89c717e8648be410024147b16e6
> 100644
> --- a/gcc/simplify-rtx.cc
> +++ b/gcc/simplify-rtx.cc
> @@ -2131,6 +2131,22 @@ simplify_const_unary_operation (enum rtx_code code,
> machine_mode mode,
> result = wide_int::from (op0, width, UNSIGNED);
> break;
>
> + case US_TRUNCATE:
> + case SS_TRUNCATE:
> + {
> + signop sgn = code == US_TRUNCATE ? UNSIGNED : SIGNED;
> + wide_int nmax
> + = wide_int::from (wi::max_value (width, sgn),
> + GET_MODE_PRECISION (imode), sgn);
> + wide_int nmin
> + = wide_int::from (wi::min_value (width, sgn),
> + GET_MODE_PRECISION (imode), sgn);
> + result
> + = wide_int::from (op0, GET_MODE_PRECISION (imode), sgn);
> + result = wi::min (wi::max (result, nmin, sgn), nmax, sgn);
FWIW, it looks like this could be:
result = wi::min (wi::max (op0, nmin, sgn), nmax, sgn);
without the first assignment to result. That feels more natural IMO,
since no conversion is being done on op0.
Thanks,
Richard
> + result = wide_int::from (result, width, sgn);
> + break;
> + }
> case SIGN_EXTEND:
> result = wide_int::from (op0, width, SIGNED);
> break;
