[Bug tree-optimization/125517] New: Wrong code for __builtin_bitreverse128

[kristerw at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125517

            Bug ID: 125517
           Summary: Wrong code for __builtin_bitreverse128
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
            Blocks: 118443
  Target Milestone: ---

The ccp1 pass is miscompiling the functions below (taken from
gcc.dg/builtin-bitreverse-8.c) when compiling for x86_64 with -O1:

#define BS(X) __builtin_bitreverse128 (X)

unsigned __int128
foo2 (unsigned __int128 a)
{
  return BS (BS (a) & 0xA0000A0000ULL);
}

unsigned __int128
foo3 (unsigned __int128 a)
{
  return BS (BS (a) | 0xA0000A0000ULL);
}

unsigned __int128
foo4 (unsigned __int128 a)
{
  return BS (BS (a) ^ 0xA0000A0000ULL);
}


The function foo2 is incorrectly optimized to `return 0`, while the other two
are incorrectly optimized to `return a`.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118443
[Bug 118443] [Meta bug] Bugs triggered by and blocking more smtgcc testing