[Bug rtl-optimization/100264] New: REE does not work on PARALLEL expressions with a single register SET child

[Bug rtl-optimization/100264] New: REE does not work on PARALLEL expressions with a single register SET child

[christophm30 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100264

            Bug ID: 100264
           Summary: REE does not work on PARALLEL expressions with a
                    single register SET child
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: christophm30 at gmail dot com
  Target Milestone: ---

REE iterates over all SET expressions and tries to eliminate redundant
zero-extensions. In case of a PARALLEL expression, there is a check in place to
ensure that "only one child of a PARALLEL expression is a SET".

Let's imagine a PARALLEL expression with two register SETs.
An example would be store-conditional, which sets a memory location (store
target) as well as a register (return success value).
The current implementation is not able to optimize a zero-extension of the
return value of store-conditional.

This can be solved, by moving the check for register targets (i.e. REG_P ())
into the function get_sub_rtx () and change the restriction of REE to "only one
child of a PARALLEL expression is a SET register".

[Bug rtl-optimization/100264] REE does not work on PARALLEL expressions with a single register SET child

[christophm30 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100264

--- Comment #1 from Christoph M. <christophm30 at gmail dot com> ---
A patch can be found here:
 https://gcc.gnu.org/pipermail/gcc-patches/2021-April/568680.html

It does not show any regressions (target riscv*).

The patch does not include a new test case to demonstrate it actually works,
because I don't know a generic way to test it.
At the moment I am testing indirectly using __atomic_compare_and_exchange () on
riscv64 to emit the required store-conditional. However, the code required for
that is not merged yet. Ideas on how to test this in a more generic way are
very much appreciated.

[Bug rtl-optimization/100264] REE does not work on PARALLEL expressions with a single register SET child

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100264

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jim Wilson <wilson@gcc.gnu.org>:

https://gcc.gnu.org/g:d5ba2eaf7032f234fdcf11d9cfc513ce7be0a255

commit r12-1168-gd5ba2eaf7032f234fdcf11d9cfc513ce7be0a255
Author: Christoph Muellner <cmuellner@gcc.gnu.org>
Date:   Mon May 10 14:39:03 2021 +0200

    REE: PR rtl-optimization/100264: Handle more PARALLEL SET expressions

    Move the check for register targets (i.e. REG_P ()) into the function
    get_sub_rtx () and change the restriction of REE to "only one child of
    a PARALLEL expression is a SET register expression" (was "only one child of
    a PARALLEL expression is a SET expression").

    This allows to handle more PARALLEL SET expressions.

    gcc/ChangeLog:
            PR rtl-optimization/100264
            * ree.c (get_sub_rtx): Ignore SET expressions without register
            destinations and remove assertion, as it is not valid anymore
            with this new behaviour.
            (merge_def_and_ext): Eliminate destination check for register
            as such SET expressions can't occur anymore.
            (combine_reaching_defs): Likewise.

[Bug rtl-optimization/100264] REE does not work on PARALLEL expressions with a single register SET child

[wilson at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100264

Jim Wilson <wilson at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |wilson at gcc dot gnu.org
         Resolution|---                         |FIXED

--- Comment #3 from Jim Wilson <wilson at gcc dot gnu.org> ---
Fixed on mainline.

[Bug rtl-optimization/100264] REE does not work on PARALLEL expressions with a single register SET child

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100264

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0