[Bug target/117726] [avr] better optimize multi-byte shifts

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117726

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Georg-Johann Lay <gjl@gcc.gnu.org>:

https://gcc.gnu.org/g:f30edd17e62e9474f90785a5915959cd6d8c3f62

commit r15-7151-gf30edd17e62e9474f90785a5915959cd6d8c3f62
Author: Georg-Johann Lay <avr@gjlay.de>
Date:   Wed Jan 22 21:11:22 2025 +0100

    AVR: PR117726 - Tweak 32-bit logical shifts of 25...30 for -Oz.

    As it turns out, logical 32-bit shifts with an offset of 25..30 can
    be performed in 7 instructions or less.  This beats the 7 instruc-
    tions required for the default code of a shift loop.
    Plus, with zero overhead, these cases can be 3-operand.

    This is only relevant for -Oz because with -Os, 3op shifts are
    split with -msplit-bit-shift (which is not performed with -Oz).

            PR target/117726
    gcc/
            * config/avr/avr.cc (avr_ld_regno_p): New function.
            (ashlsi3_out) [case 25,26,27,28,29,30]: Handle and tweak.
            (lshrsi3_out): Same.
            (avr_rtx_costs_1) [SImode, ASHIFT, LSHIFTRT]: Adjust costs.
            * config/avr/avr.md (ashlsi3, *ashlsi3, *ashlsi3_const):
            Add "r,r,C4L" alternative.
            (lshrsi3, *lshrsi3, *lshrsi3_const): Add "r,r,C4R" alternative.
            * config/avr/constraints.md (C4R, C4L): New,
    gcc/testsuite/
            * gcc.target/avr/torture/avr-torture.exp (AVR_TORTURE_OPTIONS):
            Turn one option variant into -Oz.