[Bug tree-optimization/113049] New: Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[Bug tree-optimization/113049] New: Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

            Bug ID: 113049
           Summary: Compiles to strlen even with -fno-builtin-strlen
                    -fno-optimize-strlen
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Compile with -S -Os -fno-builtin-strlen -fno-optimize-strlen

typedef __SIZE_TYPE__ size_t;

size_t strlen (const char *text)
{
  size_t len = 0;

  while (*text)
  {
    text++;
    len++;
  }
  return len;

}

Generated code:

strlen:
        b       strlen


Using built-in specs.
COLLECT_GCC=/opt/compiler-explorer/arm/gcc-12.2.0/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-gcc
Target: arm-unknown-linux-gnueabihf
Configured with: /opt/.build/arm-unknown-linux-gnueabihf/src/gcc/configure
--build=x86_64-build_pc-linux-gnu --host=x86_64-build_pc-linux-gnu
--target=arm-unknown-linux-gnueabihf
--prefix=/opt/compiler-explorer/arm/gcc-12.2.0/arm-unknown-linux-gnueabihf
--exec_prefix=/opt/compiler-explorer/arm/gcc-12.2.0/arm-unknown-linux-gnueabihf
--with-sysroot=/opt/compiler-explorer/arm/gcc-12.2.0/arm-unknown-linux-gnueabihf/arm-unknown-linux-gnueabihf/sysroot
--enable-languages=c,c++,fortran,d,objc,obj-c++,go --with-arch=armv7-a
--with-fpu=neon --with-float=hard --enable-__cxa_atexit --disable-libmudflap
--enable-libgomp --enable-libssp --enable-libquadmath
--enable-libquadmath-support --enable-libsanitizer --disable-libmpx
--with-gmp=/opt/.build/arm-unknown-linux-gnueabihf/buildtools
--with-mpfr=/opt/.build/arm-unknown-linux-gnueabihf/buildtools
--with-mpc=/opt/.build/arm-unknown-linux-gnueabihf/buildtools
--with-isl=/opt/.build/arm-unknown-linux-gnueabihf/buildtools --enable-lto
--enable-threads=posix --enable-target-optspace --disable-plugin --disable-nls
--enable-tls --disable-multilib
--with-local-prefix=/opt/compiler-explorer/arm/gcc-12.2.0/arm-unknown-linux-gnueabihf/arm-unknown-linux-gnueabihf/sysroot
--enable-long-long --with-mode=thumb
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.2.0 (GCC) 

https://godbolt.org/z/En3j6Gvda

Maybe this is same / similar to PR102725.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #1 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
-fno-builtin works, but that seems too much. -fno-builtin-strlen should switch
it off IMO.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[mikpelinux at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #2 from Mikael Pettersson <mikpelinux at gmail dot com> ---
Does -fno-tree-loop-distribute-patterns work? That's been the go-to for
disabling similar loop-to-call transformations people have been objecting to.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Mikael Pettersson from comment #2)
> Does -fno-tree-loop-distribute-patterns work? That's been the go-to for
> disabling similar loop-to-call transformations people have been objecting to.

It works. But even if it does, that's not intuitive, and -fno-builtin-strlen
should work no matter what.

And also, when a function's assembly name is "funcxyz", then the compiler
should never issue a concocted call to "funcxyz", because the assumptions of
the compiler of what "funcxyz" is doing is obviously wrong.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #4 from Andreas Schwab <schwab@linux-m68k.org> ---
-fno-builtin-strlen has a different purpose.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #5 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #4)
> -fno-builtin-strlen has a different purpose.

So then -fno-builtin should also not work? GCC documentation of -fno-builtin is
the same like for -fno-builtin-function.

At least there should be an option to disable this, e.g. you need it when
building libgcc / libc anyway, you you get silly non-functional libs.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #6 from Andreas Schwab <schwab@linux-m68k.org> ---
That's what -fno-tree-loop-distribute-patterns is for.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

--- Comment #7 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #6)
> That's what -fno-tree-loop-distribute-patterns is for.

So you know the GCC sources and can draw that conclusion.

The documentation of -ftree-loop-distribute-patterns does not relate in any way
to that.  It's impossible to find this option from a problem description.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[harald at gigawatt dot nl]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

Harald van Dijk <harald at gigawatt dot nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |harald at gigawatt dot nl

--- Comment #8 from Harald van Dijk <harald at gigawatt dot nl> ---
(In reply to Georg-Johann Lay from comment #5)
> So then -fno-builtin should also not work? GCC documentation of -fno-builtin
> is the same like for -fno-builtin-function.

-fno-builtin implies -fno-tree-loop-distribute-patterns
(https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=b15458becf4086c463cba0c42db1d8780351201b),
-fno-builtin-strlen does not, but I think you are right that that does not
match the documentation.

(In reply to Georg-Johann Lay from comment #7)
> The documentation of -ftree-loop-distribute-patterns does not relate in any
> way to that.  It's impossible to find this option from a problem description.

-ffreestanding also implies -fno-tree-loop-distribute-patterns, and that option
is documented in a way that would help here. Unless -ffreestanding is used, GCC
assumes the presence of a conforming standard library. It may expand calls to
library functions based on knowledge of what these functions do, and it may
replace code by calls to library functions as well for the same reason.

-fno-builtin and -fno-builtin-(function) are both documented as stopping the
former, but not documented as stopping the latter. The fact that one does, but
not both, is surprising.

[Bug tree-optimization/113049] Compiles to strlen even with -fno-builtin-strlen -fno-optimize-strlen

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113049

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

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

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
dup

*** This bug has been marked as a duplicate of bug 102725 ***