[Bug target/61298] redundant compare instructions for powerpc64

[pangbw at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61298

baoshan <pangbw at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |pangbw at gmail dot com

--- Comment #2 from baoshan <pangbw at gmail dot com> ---
It shows the problem in unsigned_reg_p():rtlanal.c:
 bool
  unsigned_reg_p (rtx op)
  {
    if (REG_P (op)
        && REG_EXPR (op)
        && TYPE_UNSIGNED (TREE_TYPE (REG_EXPR (op))))
      return true;

    if (GET_CODE (op) == SUBREG
        && SUBREG_PROMOTED_UNSIGNED_P (op))
      return true;

    return false;
  }
Without -m64, the first clause would return with true.
With option -m64, the 'op' comes with this formal:
(subreg:SI (reg/v:DI 126 [ c1+-7 ]) 4)
The two clauses here both return with false.

Is it legal to think the whole SUBREG expression is unsigned if the inner
EXPRESSION is unsigned? Or can I fix it with this clause?
if (GET_CODE (op) == SUBREG) return unsigned_reg_p(XEXP(op,0));