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

[Michael Meissner <meissner@linux.ibm.com>]

On Fri, Mar 03, 2023 at 03:35:44PM -0600, Segher Boessenkool wrote:
> 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.

Ok.

> 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.

Ok.

> > +/* { 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 :-(

Yep.

> 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).

Yes it is needed if GCC is configured against an older GLIBC before the full
IEEE 128-bit support was added.  For example, on my big endian test system, you
get warnings if you switch the floating point format.  I would imagine it would
also fail on little endian system with older libraries.

-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com