[Bug middle-end/112711] New: [14 Regression] possibly wrong code in bswap32(int) on llvm-16.0.6 test suite

[Bug middle-end/112711] New: [14 Regression] possibly wrong code in bswap32(int) on llvm-16.0.6 test suite

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

            Bug ID: 112711
           Summary: [14 Regression] possibly wrong code in bswap32(int) on
                    llvm-16.0.6 test suite
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Initially noticed possibly wrong code on llvm-16.0.6 test suite when building
with gcc-master from r14-5844-g9c26c91b94eb72:

  Failed Tests (2):
    LLVM-Unit :: Support/./SupportTests/Endian/Write
    LLVM-Unit :: Support/./SupportTests/Endian/WriteBitAligned

I extracted the following self-contained example:

// $ cat EndianTest.cpp
typedef          int i32;
typedef unsigned int u32;

static inline void write_i32(void *memory, i32 value) {
  // swap i32 bytes as if it was u32:
  u32 u_value = value;
  value = __builtin_bswap32(u_value);

  // llvm infers '1' alignment from destination type
  __builtin_memcpy(__builtin_assume_aligned(memory, 1), &value, sizeof(value));
}

__attribute__((noipa))
static void bug (void) {
  #define assert_eq(lhs, rhs) if (lhs != rhs) __builtin_trap()

  unsigned char data[5];
  write_i32(data, -1362446643);
  assert_eq(data[0], 0xAE);
  assert_eq(data[1], 0xCA);
  write_i32(data + 1, -1362446643);
  assert_eq(data[1], 0xAE);
}

int main() {
    bug();
}

Fails as:

$ gcc/xg++ -Bgcc EndianTest.cpp -o bug -O0 && ./bug
$ gcc/xg++ -Bgcc EndianTest.cpp -o bug -O2 && ./bug
Illegal instruction (core dumped)

$ gcc/xg++ -Bgcc -v
Reading specs from gcc/specs
COLLECT_GCC=gcc/xg++
COLLECT_LTO_WRAPPER=gcc/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/slyfox/dev/git/gcc/configure --disable-multilib
--disable-bootstrap --disable-lto --disable-libsanitizer
--disable-libstdcxx-pch --enable-languages=c,c++ --disable-libgomp
--disable-libquadmath --disable-libvtv CFLAGS='-O1 -g0' CXXFLAGS='-O1 -g0'
LDFLAGS='-O1 -g0'
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20231125 (experimental) (GCC)

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-11-25
   Target Milestone|---                         |14.0
            Summary|[14 Regression] possibly    |[14 Regression] SRA seems
                   |wrong code in bswap32(int)  |to ignore writes when using
                   |on llvm-16.0.6 test suite   |__builtin_assume_aligned
          Component|target                      |tree-optimization
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |alias

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It has nothing to do with __builtin_bswap32 really but rather
__builtin_assume_aligned and the memcpy.

SRA does not detect:
  _9 = __builtin_assume_aligned (&data, 1);
  MEM <unsigned int> [(char * {ref-all})_9] = 3451308718;
  _1 = data[0];


The store to _9 as touching data ...

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=109849
                 CC|                            |mjambor at suse dot cz

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am 90% sure it was introduced by r14-5831-gaae723d360ca26 .

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

--- Comment #3 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
I confirm bisect landed on r14-5831-gaae723d360ca26 as well.

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Possibly fails to handle RETURNS_ARG_*?

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jamborm at gcc dot gnu.org

--- Comment #5 from Martin Jambor <jamborm at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> Possibly fails to handle RETURNS_ARG_*?

Most likely.  Mine.

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

--- Comment #6 from Martin Jambor <jamborm at gcc dot gnu.org> ---
I have proposed a fix on the mailing list:

https://gcc.gnu.org/pipermail/gcc-patches/2023-November/638318.html

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Jambor <jamborm@gcc.gnu.org>:

https://gcc.gnu.org/g:302461ad9a04d82fee904bddac69811d13d5bb6a

commit r14-5971-g302461ad9a04d82fee904bddac69811d13d5bb6a
Author: Martin Jambor <mjambor@suse.cz>
Date:   Wed Nov 29 16:24:33 2023 +0100

    tree-sra: Avoid returns of references to SRA candidates

    The enhancement to address PR 109849 contained an importsnt thinko,
    and that any reference that is passed to a function and does not
    escape, must also not happen to be aliased by the return value of the
    function.  This has quickly transpired as bugs PR 112711 and PR
    112721.

    Just as IPA-modref does a good enough job to allow us to rely on the
    escaped set of variables, it sems to be doing well also on updating
    EAF_NOT_RETURNED_DIRECTLY call argument flag which happens to address
    exactly the situation we need to avoid.  Of course, if a call
    statement ignores any returned value, we also do not need to check the
    flag.

    Hopefully this does not pessimize things too much, I have verified
    that the PR 109849 testcae remains quick and so should also the
    benchmark it is derived from.

    gcc/ChangeLog:

    2023-11-27  Martin Jambor  <mjambor@suse.cz>

            PR tree-optimization/112711
            PR tree-optimization/112721
            * tree-sra.cc (build_access_from_call_arg): New parameter
            CAN_BE_RETURNED, disqualify any candidate passed by reference if it
is
            true.  Adjust leading comment.
            (scan_function): Pass appropriate value to CAN_BE_RETURNED of
            build_access_from_call_arg.

    gcc/testsuite/ChangeLog:

    2023-11-29  Martin Jambor  <mjambor@suse.cz>

            PR tree-optimization/112711
            PR tree-optimization/112721
            * g++.dg/tree-ssa/pr112711.C: New test.
            * gcc.dg/tree-ssa/pr112721.c: Likewise.

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

Martin Jambor <jamborm at gcc dot gnu.org> changed:

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

--- Comment #8 from Martin Jambor <jamborm at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/112711] [14 Regression] SRA seems to ignore writes when using __builtin_assume_aligned since r14-5831-gaae723d360ca26

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112711

--- Comment #9 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
The change also fixes llvm-16.0.6 testsuite for me. Thank you!