[Bug target/114835] New: AVR popcountqi2 is not fast&small as can be

[Bug target/114835] New: AVR popcountqi2 is not fast&small as can be

[WolfgaNg.Hospital at arcor dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114835

            Bug ID: 114835
           Summary: AVR popcountqi2 is not fast&small as can be
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: WolfgaNg.Hospital at arcor dot de
  Target Milestone: ---

Created attachment 58025
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58025&action=edit
AVR assembly code for __popcountqi2

For 8-bit AVRs, the current 16-instruction __popcountqi2 uses 6 ADC
instructions to establish the number of bits set in a byte.  
In "Bit Twiddling Hacks", Sean E. Anderson presents several approaches to this;
"parallel/sideways addition" can be coded with one instruction&cycle less.

When establishing the "popcount" of an uint8_t, I've seen GCC to widen the
value to "half int" and use __popcountqi2 twice.

[Bug target/114835] AVR popcountqi2 is not fast&small as can be

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114835

--- Comment #1 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:8d2c93fcfe1afc5291bbbe162c3b7ad5764f6d8d

commit r15-286-g8d2c93fcfe1afc5291bbbe162c3b7ad5764f6d8d
Author: Wolfgang Hospital <Wolfgang.Hospital@arcor.de>
Date:   Tue May 7 16:24:39 2024 +0200

    AVR: target/114835 - Tweak popcountqi2

    libgcc/
            PR target/114835
            * config/avr/lib1funcs.S (__popcountqi2): Use code that
            is one instruction shorter / faster.

[Bug target/114835] AVR popcountqi2 is not fast&small as can be

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114835

Georg-Johann Lay <gjl at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Fixed in v15.

[Bug target/114835] AVR popcountqi2 is not fast&small as can be

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114835

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Wolfgang Hospital from comment #0)
> When establishing the "popcount" of an uint8_t, I've seen GCC to widen the
> value to "half int" and use __popcountqi2 twice.

This is a different issue, please f'up PR114975.