[Bug rtl-optimization/110254] New: improve_allocation() routine does not update allocated_hardreg_p[] array

[Bug rtl-optimization/110254] New: improve_allocation() routine does not update allocated_hardreg_p[] array

[jskumari at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110254

            Bug ID: 110254
           Summary: improve_allocation() routine does not update
                    allocated_hardreg_p[] array
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jskumari at gcc dot gnu.org
  Target Milestone: ---

"allocated_hardreg_p[]" is a boolean array whose element value is TRUE is the
corresponding hard register was already allocated for an allocno.
This array is used in calculate_saved_nregs().

The improve_allocation() function improves the allocation by spilling some
allocnos and assigning the freed hard registers to other allocnos if it
decreases the overall allocation cost.

If the register chosen in improve_allocation() is one that already has been
assigned to a conflicting allocno, then allocated_hardreg_p[] already has the
corresponding bit set to TRUE, so nothing needs to be done.

But improve_allocation() can also choose a register that has not been assigned
to a conflicting allocno, and also has not been assigned to any other allocno.
In this case, allocated_hardreg_p[] has to be updated. improve_allocation()
calls assign_hard_reg() to check if any of the spilled allocnos can get hard
registers.
And assign_hard_reg() calls calculate_saved_nregs() which uses the array.
Hence, the array needs to be updated.

[Bug rtl-optimization/110254] improve_allocation() routine does not update allocated_hardreg_p[] array

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110254

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Off topic / pet peeve: it's not an array of functions, so it should not be
called
something_p .

[Bug rtl-optimization/110254] improve_allocation() routine does not update allocated_hardreg_p[] array

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110254

--- Comment #2 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Surya Kumari Jangala from comment #0)
> But improve_allocation() can also choose a register that has not been
> assigned to a conflicting allocno, and also has not been assigned to any
> other allocno. In this case, allocated_hardreg_p[] has to be updated.
> improve_allocation() calls assign_hard_reg() to check if any of the spilled
> allocnos can get hard registers.

Be cognizant of if the allocno we're reassigning to another "hardreg", has a
mode that represents a register pair or larger, you'll need to update multiple
allocated_hardreg_p[] entries.

[Bug rtl-optimization/110254] improve_allocation() routine does not update allocated_hardreg_p[] array

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110254

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Surya Kumari Jangala
<jskumari@gcc.gnu.org>:

https://gcc.gnu.org/g:02ecc9a26324d142c5cd19d24526b9c23aabc1c3

commit r14-3251-g02ecc9a26324d142c5cd19d24526b9c23aabc1c3
Author: Surya Kumari Jangala <jskumari@linux.ibm.com>
Date:   Mon Aug 14 09:34:56 2023 -0500

    ira: update allocated_hardreg_p[] in improve_allocation() [PR110254]

    The improve_allocation() routine does not update the
    allocated_hardreg_p[] array after an allocno is assigned a register.

    If the register chosen in improve_allocation() is one that already has
    been assigned to a conflicting allocno, then allocated_hardreg_p[]
    already has the corresponding bit set to TRUE, so nothing needs to be
    done.

    But improve_allocation() can also choose a register that has not been
    assigned to a conflicting allocno, and also has not been assigned to any
    other allocno. In this case, allocated_hardreg_p[] has to be updated.

    2023-07-21  Surya Kumari Jangala  <jskumari@linux.ibm.com>

    gcc/
            PR rtl-optimization/110254
            * ira-color.cc (improve_allocation): Update array
            allocated_hard_reg_p.