[Bug target/117477] Register allocator chooses a slot location instead a new callee saved register and not taking inot account pair allocation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117477

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Richard Sandiford <rsandifo@gcc.gnu.org>:

https://gcc.gnu.org/g:e836d80374aa03a5ea5bd6cca00d826020c461da

commit r15-7852-ge836d80374aa03a5ea5bd6cca00d826020c461da
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Mar 6 11:06:25 2025 +0000

    ira: Add new hooks for callee-save vs spills [PR117477]

    Following on from the discussion in:

      https://gcc.gnu.org/pipermail/gcc-patches/2025-February/675256.html

    this patch removes TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE and
    replaces it with two hooks: one that controls the cost of using an
    extra callee-saved register and one that controls the cost of allocating
    a frame for the first spill.

    (The patch does not attempt to address the shrink-wrapping part of
    the thread above.)

    On AArch64, this is enough to fix PR117477, as verified by the new tests.
    The patch does not change the SPEC2017 scores significantly.  (I saw a
    slight improvement in fotonik3d and roms, but I'm not convinced that
    the improvements are real.)

    The patch makes IRA use caller saves for gcc.target/aarch64/pr103350-1.c,
    which is a scan-dump correctness test that relies on not using
    caller saves.  The decision to use caller saves looks appropriate,
    and saves an instruction, so I've just added -fno-caller-saves
    to the test options.

    The x86 parts were written by Honza.

    gcc/
            PR rtl-optimization/117477
            * config/aarch64/aarch64.cc (aarch64_count_saves): New function.
            (aarch64_count_above_hard_fp_saves, aarch64_callee_save_cost)
            (aarch64_frame_allocation_cost): Likewise.
            (TARGET_CALLEE_SAVE_COST): Define.
            (TARGET_FRAME_ALLOCATION_COST): Likewise.
            * config/i386/i386.cc (ix86_ira_callee_saved_register_cost_scale):
            Replace with...
            (ix86_callee_save_cost): ...this new hook.
            (TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE): Delete.
            (TARGET_CALLEE_SAVE_COST): Define.
            * target.h (spill_cost_type, frame_cost_type): New enums.
            * target.def (callee_save_cost, frame_allocation_cost): New hooks.
            (ira_callee_saved_register_cost_scale): Delete.
            * doc/tm.texi.in (TARGET_IRA_CALLEE_SAVED_REGISTER_COST_SCALE):
Delete.
            (TARGET_CALLEE_SAVE_COST, TARGET_FRAME_ALLOCATION_COST): New hooks.
            * doc/tm.texi: Regenerate.
            * hard-reg-set.h (hard_reg_set_popcount): New function.
            * ira-color.cc (allocated_memory_p): New variable.
            (allocated_callee_save_regs): Likewise.
            (record_allocation): New function.
            (assign_hard_reg): Use targetm.frame_allocation_cost to model
            the cost of the first spill or first caller save.  Use
            targetm.callee_save_cost to model the cost of using new
callee-saved
            registers.  Apply the exit rather than entry frequency to the cost
            of restoring a register or deallocating the frame.  Update the
            new variables above.
            (improve_allocation): Use record_allocation.
            (color): Initialize allocated_callee_save_regs.
            (ira_color): Initialize allocated_memory_p.
            * targhooks.h (default_callee_save_cost): Declare.
            (default_frame_allocation_cost): Likewise.
            * targhooks.cc (default_callee_save_cost): New function.
            (default_frame_allocation_cost): Likewise.

    gcc/testsuite/
            PR rtl-optimization/117477
            * gcc.target/aarch64/callee_save_1.c: New test.
            * gcc.target/aarch64/callee_save_2.c: Likewise.
            * gcc.target/aarch64/callee_save_3.c: Likewise.
            * gcc.target/aarch64/pr103350-1.c: Add -fno-caller-saves.

    Co-authored-by: Jan Hubicka <hubicka@ucw.cz>