[Bug c++/59394] New: Unused code generated

[Bug c++/59394] New: Unused code generated

[smal.root at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

            Bug ID: 59394
           Summary: Unused code generated
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: smal.root at gmail dot com
            Target: AVR

Created attachment 31385
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31385&action=edit
source code

GCC:
avr-gcc -v
Using built-in specs.
COLLECT_GCC=avr-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/avr/4.8.2/lto-wrapper
Target: avr
Configured with: /build/avr-gcc/src/gcc-4.8.2/configure
--disable-cloog-version-check --disable-install-libiberty --disable-libssp
--disable-libstdcxx-pch --disable-libunwind-exceptions
--disable-linker-build-id --disable-nls --disable-werror --enable-__cxa_atexit
--enable-checking=release --enable-clocale=gnu --enable-cloog-backend=isl
--enable-gnu-unique-object --enable-gold --enable-languages=c,c++
--enable-ld=default --enable-lto --enable-plugin --enable-shared
--infodir=/usr/share/info --libdir=/usr/lib --libexecdir=/usr/lib
--mandir=/usr/share/man --prefix=/usr --target=avr --with-as=/usr/bin/avr-as
--with-gnu-as --with-gnu-ld --with-ld=/usr/bin/avr-ld --with-plugin-ld=ld.gold
--with-system-zlib
Thread model: single
gcc version 4.8.2 (GCC) 

OS:
Arch Linux 
Linux 3.12.0-1-ARCH #1 SMP PREEMPT Wed Nov 6 09:06:27 CET 2013 x86_64 GNU/Linux

Command line:
avr-gcc -Wall -mmcu=atxmega64a3 -DF_CPU=16000000UL  -mno-interrupts -Os
-pedantic-errors -pedantic -std=c++11 -Wfatal-errors -Wall   
-I/usr/avr/include  -c main.cpp -o obj/Release/main.o
main.cpp: In function 'int main()':
main.cpp:55:21: warning: variable 'tval32' set but not used
[-Wunused-but-set-variable]
   volatile uint32_t tval32;
                     ^
avr-g++  -o bin/Release/lambda_test.elf obj/Release/main.o   -mmcu=atxmega64a3
-Wl,-Map=bin/Release/lambda_test.map,--cref  
Output size is 7,92 KB
Running project post-build steps
avr-size bin/Release/lambda_test.elf
   text       data        bss        dec        hex    filename
    850          0       2400       3250        cb2   
bin/Release/lambda_test.elf
avr-objdump -h -S bin/Release/lambda_test.elf > bin/Release/lambda_test.lss
Process terminated with status 0 (0 minutes, 0 seconds)
0 errors, 1 warnings (0 minutes, 0 seconds)

Source file: attached main.cpp
Generated assembly: attached lambda_test.lss

Problem.
A. As you can see in generated assembly:
1. function Sort_OldStyle(_Z13Sort_OldStylev) contain(as inline) functions Sort
and Sort_OldStyle_Internal
2. function Sort_NewStyle(_Z13Sort_NewStylev) contain(as inline) functions Sort
and lambda-expression

B. But also generated code contain unneded:
1. function Sort(_Z4SortPV5SPairS1_PFvRS0_E)
2. function Sort_OldStyle_Internal(_Z22Sort_OldStyle_InternalRV5SPair)
3. lambda-expression(_ZZ13Sort_NewStylevENUlRV5SPairE_4_FUNES1_)

Why gcc include functions from B-list if they already exist in functions of
list A? Also why gcc use inline for function Sort and don't use call with -Os
used?

[Bug c++/59394] Unused code generated

[smal.root at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

--- Comment #1 from smalcom <smal.root at gmail dot com> ---
Created attachment 31386
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31386&action=edit
generated assembly

[Bug c++/59394] Unused code generated

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #31385|0                           |1
        is obsolete|                            |

--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Created attachment 31500
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31500&action=edit
C++ source.

Please follow the bug reporting instructions and don't include headers,
especcialy ones that the common GCC developer does not have.

Attached a source file that compiles fine without headers.

And there is nothing avr specific here.

[Bug c++/59394] Unused code generated

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|AVR                         |
           Severity|major                       |normal

[Bug c++/59394] Unused code generated

[gjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Some more notes:

If you don't want that small functions are being inlined, consider
-fno-inline-small-functions.

If a function is being inlined then it's body is still implemented except in
the case where GCC can prove the body is never needed, for example if the
function is static.

If you implement two functions that result in the same code, GCC won't reuse
the code for you.  If you have redundant code, it is up to you to reuse it.

[Bug middle-end/59394] Unused code generated

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

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

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

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
If I use -Wl,--gc-sections -ffunction-sections, then all of the unused
(non-static) functions are removed.

Also -flto is able to optimize it too.

[Bug middle-end/59394] Unused code generated

[smal.root at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

--- Comment #5 from smalcom <smal.root at gmail dot com> ---
Created attachment 52049
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52049&action=edit
Generated assembly when using "gc-section". avr-gcc-10.2

[Bug middle-end/59394] Unused code generated

[smal.root at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59394

--- Comment #6 from smalcom <smal.root at gmail dot com> ---
Created attachment 52050
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52050&action=edit
Generated assembly when using "LTO". avr-gcc-10.2

(In reply to Andrew Pinski from comment #4)
> If I use -Wl,--gc-sections -ffunction-sections, then all of the unused
> (non-static) functions are removed.
> 
> Also -flto is able to optimize it too.

I confirm that:
1. With set "-Wl,--gc-sections -ffunction-sections" output file do not contain
unused functions (attached gcsec.lss).
2. With "-flto" all functions are inlined and present only used code (attached
lto.lss).

Tested using gcc-10:

avr-gcc -v
Using built-in specs.
Reading specs from
/mnt/stor5/opt/сборка/avr-10.2.0/bin/../lib/gcc/avr/10.2.0/device-specs/specs-avr2
COLLECT_GCC=avr-gcc
COLLECT_LTO_WRAPPER=/mnt/stor5/opt/сборка/avr-10.2.0/bin/../libexec/gcc/avr/10.2.0/lto-wrapper
Target: avr
Configured with: ../configure --prefix=/opt/toolchain/avr-10.2.0 --target=avr
--enable-languages=c,c++ --disable-nls --disable-libssp --with-dwarf2
Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.0 (GCC) 

Great. Thanks!