[Bug target/105359] New: _Float128 expanders and builtins disabled on ppc targets with 64-bit long double

[Bug target/105359] New: _Float128 expanders and builtins disabled on ppc targets with 64-bit long double

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105359

            Bug ID: 105359
           Summary: _Float128 expanders and builtins disabled on ppc
                    targets with 64-bit long double
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aoliva at gcc dot gnu.org
  Target Milestone: ---
            Target: rs6000

As described elsewhere, some tests fail on targets with 64-bit long double,
because of patterns that (IMHO incorrectly) use TARGET_LONG_DOUBLE_128 in their
conditions, and because of type compatibility tests that only accept _Float128
types under the same condition.
https://gcc.gnu.org/pipermail/gcc-patches/2022-April/593257.html
https://gcc.gnu.org/pipermail/gcc-patches/2022-April/593515.html

There doesn't seem to be a reason for the patterns to conditioned on long
double being a 128-bit type: that's too strict.  A laxer condition, covering
the requirements for _Float128 to be *supported*, ought to be enough. 
Furthermore, there doesn't seem to be any reason for -mlong-double-64 to
disable those patterns even on target variants that use 128-bit long double.

It's too late to fix this for GCC 12, but hopefully some rs6000/powerpc
maintainer will agree that there's no reason to tie support for insn patterns
and builtins for _Float128 with long double's being the same type as _Float128.

It looks like all of the troublesome patterns have TARGET_HARD_FLOAT &&
TARGET_LONG_DOUBLE_128.  I hope this problem could be fixed by replacing the
latter with TARGET_FLOAT128_TYPE, but I'll defer to more knowledgeable port
maintainers.

[Bug target/105359] _Float128 expanders and builtins disabled on ppc targets with 64-bit long double

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105359

--- Comment #1 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
pr82748-1.c is another victim of this issue.  do_copysign_ld needs to convert
between (64-bit) long double and __ieee128 for __builtin_copysignq, and since
the expanders for these conversions are conditioned on TARGET_LONG_DOUBLE_128,
we end up issuing libcalls, but the test doesn't want any 'bl' opcode.

[Bug target/105359] _Float128 expanders and builtins disabled on ppc targets with 64-bit long double

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105359

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2024-04-23
           Keywords|                            |missed-optimization
           Assignee|unassigned at gcc dot gnu.org      |linkw at gcc dot gnu.org
                 CC|                            |linkw at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Kewen Lin <linkw at gcc dot gnu.org> ---
Thanks for reporting, I'll have a look.