[Bug rtl-optimization/52883] ICE in simplify_const_unary_operation, at simplify-rtx.c:1464

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52883

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
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             Status|ASSIGNED                    |NEW
         AssignedTo|ubizjak at gmail dot com    |unassigned at gcc dot
                   |                            |gnu.org

--- Comment #6 from Uros Bizjak <ubizjak at gmail dot com> 2012-04-06 12:36:06 UTC ---
(In reply to comment #3)

> Just that it makes no sense.  Please fix whoever generated it instead.

OK, tracing this a bit deeper:

#0  internal_error (gmsgid=0x111f5e0 "in %s, at %s:%d") at
../../gcc-svn/trunk/gcc/diagnostic.c:839
#1  0x0000000000e1cda4 in fancy_abort (file=<optimized out>, line=1464,
function=0xef4380 "simplify_const_unary_operation")
    at ../../gcc-svn/trunk/gcc/diagnostic.c:899
#2  0x0000000000881783 in simplify_const_unary_operation (code=<optimized out>,
mode=DImode, op=0x7ffff19ad470, op_mode=<optimized out>)
    at ../../gcc-svn/trunk/gcc/simplify-rtx.c:1464
#3  0x000000000087f4d0 in simplify_unary_operation (code=ZERO_EXTEND,
mode=DImode, op=0x7ffff19ad470, op_mode=VOIDmode)
    at ../../gcc-svn/trunk/gcc/simplify-rtx.c:579
#4  0x00000000005ec860 in cselib_expand_value_rtx_1 (orig=<optimized out>,
evd=0x7fffffffd950, max_depth=<optimized out>)
    at ../../gcc-svn/trunk/gcc/cselib.c:1805

The problem starts at cselib.c, where:

  /* If an operand has been simplified into CONST_INT, which doesn't
     have a mode and the mode isn't derivable from whole rtx's mode,
     try simplify_*_operation first with mode from original's operand
     and as a fallback wrap CONST_INT into gen_rtx_CONST.  */

We do have specializations for this case:

  switch (GET_RTX_CLASS (code))
    {
    case RTX_UNARY:
      if (CONST_INT_P (XEXP (copy, 0))
      && GET_MODE (XEXP (orig, 0)) != VOIDmode)
    {
      scopy = simplify_unary_operation (code, mode, XEXP (copy, 0),
                        GET_MODE (XEXP (orig, 0)));
      if (scopy)
        return scopy;
    }
      break;
  ...

But, since we have VOIDmode operand, we should do as the comment says and wrap
CONST_INT with CONST. However, we directly hit:

  scopy = simplify_rtx (copy);
  if (scopy)
    return scopy;
  return copy;

where simplify_rtx just passes problematic RTX to simplify_unary_operation.

Leaving this to RTX experts, since the code does not match the comment.