[Bug target/119971] New: RISC-V: Wrong code with bitmanip extension

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119971

            Bug ID: 119971
           Summary: RISC-V: Wrong code with bitmanip extension
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

Compiling with -O3 -march=rv64gcb causes the function foo below to be
miscompiled:

__attribute__ ((noipa)) unsigned
foo (unsigned b, unsigned e, unsigned i)
{
  e >>= b;
  i >>= e & 31;
  return i & 1;
}

int main()
{
  if (foo (0x18, 0xfe000000, 0x40000000) != 1)
    __builtin_abort ();
  return 0;
}


The generated assembly fails to take the masking & 31 into account:

foo:
        srlw    a1,a1,a0
        bext    a0,a2,a1
        ret