Re: [PATCH 2/2] Rework 128-bit complex multiply and divide.

[Segher Boessenkool <segher@kernel.crashing.org>]

Hi!

On Fri, Feb 03, 2023 at 12:53:05AM -0500, Michael Meissner wrote:
> This patch reworks how the complex multiply and divide built-in functions are
> done.

> I tested all 3 patchs for PR target/107299 on:

Is this part of the proposed commit message?  As Ke Wen pointed out, it
is wrong.  Most of your mail does not belong in a commit message at all,
but some probably does?  Please do this clearer with future patches.

> 	* config/rs6000/rs6000.cc (create_complex_muldiv): Delete.
> 	(init_float128_ieee): Delete code to switch complex multiply and divide
> 	for long double.

I like this kind of patch :-)

> +/* Internal function to return the built-in function id for the complex
> +   multiply operation for a given mode.  */
> +
> +static inline built_in_function
> +complex_multiply_builtin_code (machine_mode mode)
> +{
> +  return (built_in_function) (BUILT_IN_COMPLEX_MUL_MIN + mode
> +			      - MIN_MODE_COMPLEX_FLOAT);
> +}

There should be an assert that the mode is as expected
  gcc_assert (IN_RANGE (mode, MIN_MODE_COMPLEX_FLOAT, MAX_MODE_COMPLEX_FLOAT));
or such.

Using more temporaries should make this simpler as well, obviate the
need for explicit casts, and make everything fit on short lines.

> +static inline built_in_function
> +complex_divide_builtin_code (machine_mode mode)
> +{
> +  return (built_in_function) (BUILT_IN_COMPLEX_DIV_MIN + mode
> +			      - MIN_MODE_COMPLEX_FLOAT);
> +}

Ditto ofc.

> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/divic3-1.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile { target { powerpc*-*-* } } } */

Leave the target clause out.

> +/* { dg-require-effective-target powerpc_p8vector_ok } */
> +/* { dg-require-effective-target longdouble128 } */
> +/* { dg-require-effective-target ppc_float128_sw } */
> +/* { dg-options "-O2 -mpower8-vector -mabi=ieeelongdouble -Wno-psabi" } */

It would be nice if you did not try to add -mpower8-vector in more
testcases :-(

Is -Wno-psabi needed here?  What is the error you get without it / on
which configurations?  Cargo-culting hiding the warnings makes you see
fewer warnings, but that is the opposite of a good idea.

> +/* { dg-final { scan-assembler "bl __divtc3" } } */

This name depends on what object format and ABI is in use (some have an
extra leading underscore, or a dot, or whatever).


Segher