[Bug tree-optimization/113370] New: wrong code with shift and _BitInt() at -O0

[Bug tree-optimization/113370] New: wrong code with shift and _BitInt() at -O0

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113370

            Bug ID: 113370
           Summary: wrong code with shift and _BitInt() at -O0
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

Created attachment 57066
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57066&action=edit
reduced testcase

Output:
$ x86_64-pc-linux-gnu-gcc testcase.c
$ ./a.out 
Aborted

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r14-7215-20240112190107-g8b447fa89d5-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/14.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r14-7215-20240112190107-g8b447fa89d5-checking-yes-rtl-df-extra-nobootstrap-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.1 20240112 (experimental) (GCC)

[Bug tree-optimization/113370] wrong code with shift and _BitInt() at -O0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113370

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-01-13
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

Testcase which shows what something is wrong with the original value:
```
typedef _BitInt(255) B;

[[gnu::noipa]]
B
foo(int s)
{
  B a = 0;
  a = (-(B)3) >> s;
  return a;
}

int
main(void)
{
  B x = foo(51);
  unsigned long *a = (unsigned long *)&x;
  __builtin_printf("%lx\n", a[0]);
  __builtin_printf("%lx\n", a[1]);
  __builtin_printf("%lx\n", a[2]);
  __builtin_printf("%lx\n", a[3]);
  //if (x != -1)
  //  __builtin_abort();
  return 0;
}
```

[Bug tree-optimization/113370] wrong code with shift and _BitInt() at -O0

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113370

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 57071
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57071&action=edit
gcc14-pr113370.patch

Untested fix.

[Bug tree-optimization/113370] wrong code with shift and _BitInt() at -O0

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113370

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:8a1927856a10c5ff1b86504c345c8be449b53c30

commit r14-7239-g8a1927856a10c5ff1b86504c345c8be449b53c30
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Jan 15 09:58:37 2024 +0100

    lower-bitint: Fix up handling of INTEGER_CSTs in handle_operand in right
shifts or comparisons [PR113370]

    The INTEGER_CST code uses the remainder bits in computations whether to use
    whole constant or just part of it and extend it at runtime, and furthermore
    uses it to avoid using all bits even when using the (almost) whole
constant.
    The problem is that the prec % (2 * limb_prec) computation it uses is
    appropriate only for the normal lowering of mergeable operations (where
    we process 2 limbs at a time in a loop starting with least significant
    limbs and process the remaining 0-2 limbs after the loop (there with
    constant indexes).  For that case it is ok not to emit the upper
    prec % (2 * limb_prec) bits into the constant, because those bits will be
    extracted using INTEGER_CST idx and so will be used directly in the
    statements as INTEGER_CSTs.
    For other cases, where we either process just a single limb in a loop,
    process it downwards (e.g. non-equality comparisons) or with some runtime
    addends (some shifts), there is either just at most one limb lowered with
    INTEGER_CST idx after the loop (e.g. for right shift) or before the loop
    (e.g. non-equality comparisons), or all limbs are processed with
    non-INTEGER_CST indexes (e.g. for left shift, when m_var_msb is set).
    Now, the m_var_msb case is already handled through
                  if (m_var_msb)
                    type = TREE_TYPE (op);
                  else
                    /* If we have a guarantee the most significant partial limb
                       (if any) will be only accessed through handle_operand
                       with INTEGER_CST idx, we don't need to include the
partial
                       limb in .rodata.  */
                    type = build_bitint_type (prec - rem, 1);
    but for the right shifts or comparisons the prec - rem when rem was
    prec % (2 * limb_prec) was incorrect, so the following patch fixes it
    to use remainder for 2 limbs only if m_upwards_2limb and remainder for
    1 limb otherwise.

    2024-01-15  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/113370
            * gimple-lower-bitint.cc (bitint_large_huge::handle_operand): Only
            set rem to prec % (2 * limb_prec) if m_upwards_2limb, otherwise
            set it to just prec % limb_prec.

            * gcc.dg/torture/bitint-48.c: New test.

[Bug tree-optimization/113370] wrong code with shift and _BitInt() at -O0

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113370

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|---                         |14.0
         Resolution|---                         |FIXED

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed, thanks for the report.