[Bug c/106017] New: [PowerPC] No array-to-pointer conversion for MMA accumulator

[Bug c/106017] New: [PowerPC] No array-to-pointer conversion for MMA accumulator

[nemanja.i.ibm at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

            Bug ID: 106017
           Summary: [PowerPC] No array-to-pointer conversion for MMA
                    accumulator
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nemanja.i.ibm at gmail dot com
  Target Milestone: ---

It appears that the typical array to pointer conversion for function arguments
does not work for MMA accumulator types. The user has to explicitly convert.

Code:
$ cat aa.c 
void takeacc(__vector_quad *);
void passacc() {
        __vector_quad arr[4];
#ifdef _EXPLICIT
        takeacc(&arr[0]);
#else
        takeacc(arr);
#endif
}

Compile (success):
$ gcc -mcpu=power10 -O3 aa.c -S -D_EXPLICIT && echo Success
Success

Compile (failure):
$ gcc -mcpu=power10 -O3 aa.c -S && echo Success
aa.c: In function 'passacc':
aa.c:7:9: error: invalid conversion to type '* __vector_quad'
    7 |         takeacc(arr);
      |         ^~~~~~~

Version:
$ gcc --version
gcc (GCC) 12.1.1 20220524 [releases/gcc-12 r12-8410-gf0a0aeec44]
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-06-17

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Confirmed.

C allows to convert a pointer to data to any other pointer to data (possibly
modulo alignment restrictions).  What is *not* valid is accessing anything via
a type not compatible with its effective type (or via a character type).

So the restriction in rs6000_invalid_conversion errors for valid C programs.
What was it intended to accomplish?

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #2 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #1)
> So the restriction in rs6000_invalid_conversion errors for valid C programs.
> What was it intended to accomplish?

We do not want or allow automatic conversions between the opaque __vector_pair
and __vector_quad types and other types and those are correctly disallowed
there.  Conversions between those types needs to go through the builtins
defined for that.

As for the pointer conversions tested there, I guess they came along for the
ride?  Nemanja, do you remember the history there?  Or does LLVM allow the
pointer conversions and it's just GCC that complains?

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #3 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Peter Bergner from comment #2)
> We do not want or allow automatic conversions between the opaque
> __vector_pair and __vector_quad types and other types and those are
> correctly disallowed there.

Of course, but that is not what this is about...

> As for the pointer conversions tested there, I guess they came along for the
> ride?  Nemanja, do you remember the history there?  Or does LLVM allow the
> pointer conversions and it's just GCC that complains?

... this is.

Possibly the restriction prevents some ICEs elsewhere, but those just need to
be solved then, not hidden.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[nemanja.i.ibm at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #4 from Nemanja Ivanovic <nemanja.i.ibm at gmail dot com> ---
(In reply to Peter Bergner from comment #2)
> (In reply to Segher Boessenkool from comment #1)
> > So the restriction in rs6000_invalid_conversion errors for valid C programs.
> > What was it intended to accomplish?
> 
> We do not want or allow automatic conversions between the opaque
> __vector_pair and __vector_quad types and other types and those are
> correctly disallowed there.  Conversions between those types needs to go
> through the builtins defined for that.
> 
> As for the pointer conversions tested there, I guess they came along for the
> ride?  Nemanja, do you remember the history there?  Or does LLVM allow the
> pointer conversions and it's just GCC that complains?

Yes, the desired semantics are to disallow implicit or explicit conversions
from these types to any other types. But pointer casts (presumably including
reinterpret_cast in C++) should be fair game. Clang allows these conversions.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |segher at gcc dot gnu.org

--- Comment #5 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Okay, I'll handle it.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> ---
FWIW, reinterpret_cast allows exactly the same things as C casts (but with the
obvious C++ extensions: member objects, member functions, C++'s concept of
lvalue, that kins of thing).  It is not similar to bit_cast at all.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

Peter Bergner <bergner at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #7 from Peter Bergner <bergner at gcc dot gnu.org> ---
I think we just want to remove the entire section in
rs6000_invalid_conversion() that checks the XOmode/OOmode pointer conversions. 
Doing that fixes the ICE and fixes the PR106015 ICE too.  I'm doing a bootstrap
and regtest of that patch now.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #8 from Peter Bergner <bergner at gcc dot gnu.org> ---
*** Bug 106015 has been marked as a duplicate of this bug. ***

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #9 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Peter Bergner from comment #7)
> I think we just want to remove the entire section in
> rs6000_invalid_conversion() that checks the XOmode/OOmode pointer
> conversions.  Doing that fixes the ICE and fixes the PR106015 ICE too.  I'm
> doing a bootstrap and regtest of that patch now.

Testing was clean, so I'll submit the patch.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Peter Bergner <bergner@gcc.gnu.org>:

https://gcc.gnu.org/g:1ae1325f24cea1698b56e4299d95446a1f7b90a2

commit r13-2239-g1ae1325f24cea1698b56e4299d95446a1f7b90a2
Author: Peter Bergner <bergner@linux.ibm.com>
Date:   Sat Aug 27 19:44:16 2022 -0500

    rs6000: Allow conversions of MMA pointer types [PR106017]

    GCC incorrectly disables conversions between MMA pointer types, which
    are allowed with clang.  The original intent was to disable conversions
    between MMA types and other other types, but pointer conversions should
    have been allowed.  The fix is to just remove the MMA pointer conversion
    handling code altogether.

    gcc/
            PR target/106017
            * config/rs6000/rs6000.cc (rs6000_invalid_conversion): Remove
handling
            of MMA pointer conversions.

    gcc/testsuite/
            PR target/106017
            * gcc.target/powerpc/pr106017.c: New test.

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Peter Bergner
<bergner@gcc.gnu.org>:

https://gcc.gnu.org/g:22ff125247ff5328ad4544aef939d491618d714d

commit r12-8726-g22ff125247ff5328ad4544aef939d491618d714d
Author: Peter Bergner <bergner@linux.ibm.com>
Date:   Sat Aug 27 19:44:16 2022 -0500

    rs6000: Allow conversions of MMA pointer types [PR106017]

    GCC incorrectly disables conversions between MMA pointer types, which
    are allowed with clang.  The original intent was to disable conversions
    between MMA types and other other types, but pointer conversions should
    have been allowed.  The fix is to just remove the MMA pointer conversion
    handling code altogether.

    gcc/
            PR target/106017
            * config/rs6000/rs6000.cc (rs6000_invalid_conversion): Remove
handling
            of MMA pointer conversions.

    gcc/testsuite/
            PR target/106017
            * gcc.target/powerpc/pr106017.c: New test.

    (cherry picked from commit 1ae1325f24cea1698b56e4299d95446a1f7b90a2)

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Peter Bergner
<bergner@gcc.gnu.org>:

https://gcc.gnu.org/g:f494a85f0bf653c3128b376c1abf821a27748c11

commit r11-10227-gf494a85f0bf653c3128b376c1abf821a27748c11
Author: Peter Bergner <bergner@linux.ibm.com>
Date:   Sat Aug 27 19:44:16 2022 -0500

    rs6000: Allow conversions of MMA pointer types [PR106017]

    GCC incorrectly disables conversions between MMA pointer types, which
    are allowed with clang.  The original intent was to disable conversions
    between MMA types and other other types, but pointer conversions should
    have been allowed.  The fix is to just remove the MMA pointer conversion
    handling code altogether.

    gcc/
            PR target/106017
            * config/rs6000/rs6000.c (rs6000_invalid_conversion): Remove
handling
            of MMA pointer conversions.

    gcc/testsuite/
            PR target/106017
            * gcc.target/powerpc/pr106017.c: New test.

    (cherry picked from commit 1ae1325f24cea1698b56e4299d95446a1f7b90a2)

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

--- Comment #13 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Peter Bergner
<bergner@gcc.gnu.org>:

https://gcc.gnu.org/g:3927bd9f9150576f2905c8930732c419f1850fca

commit r10-10966-g3927bd9f9150576f2905c8930732c419f1850fca
Author: Peter Bergner <bergner@linux.ibm.com>
Date:   Sat Aug 27 19:44:16 2022 -0500

    rs6000: Allow conversions of MMA pointer types [PR106017]

    GCC incorrectly disables conversions between MMA pointer types, which
    are allowed with clang.  The original intent was to disable conversions
    between MMA types and other other types, but pointer conversions should
    have been allowed.  The fix is to just remove the MMA pointer conversion
    handling code altogether.

    gcc/
            PR target/106017
            * config/rs6000/rs6000.c (rs6000_invalid_conversion): Remove
handling
            of MMA pointer conversions.

    gcc/testsuite/
            PR target/106017
            * gcc.target/powerpc/pr106017.c: New test.

    (cherry picked from commit 1ae1325f24cea1698b56e4299d95446a1f7b90a2)

[Bug target/106017] [PowerPC] No array-to-pointer conversion for MMA accumulator

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106017

Peter Bergner <bergner at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.0, 11.0, 12.0, 13.0
             Status|ASSIGNED                    |RESOLVED
           Assignee|segher at gcc dot gnu.org          |bergner at gcc dot gnu.org
         Resolution|---                         |FIXED

--- Comment #14 from Peter Bergner <bergner at gcc dot gnu.org> ---
Fixed everywhere.