--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 16 Feb 2017, mpolacek at gcc dot wrote:

> --- Comment #6 from Marek Polacek <mpolacek at gcc dot> ---
> Yes, but see my Comment 3 regarding STRIP_SIGN_NOPS.
> Also the typedef is necessary, otherwise there are no NOP_EXPRs (huh).

Yeah, but the issue is really


    case NOP_EXPR:
      /* Convert -((double)float) into (double)(-float).  */
      if (TREE_CODE (type) == REAL_TYPE)
          tem = strip_float_extensions (t);
          if (tem != t && negate_expr_p (tem))
            return fold_convert_loc (loc, type, negate_expr (tem));

vs. negate_expr_p:


the type stripping has to be consistent.  Thus the fix is to
add the same STRIP_SIGN_NOPS to fold_negate_expr (negate_expr
does it as well!) or to remove it everywhere and handle the
cases allowed in case NOP_EXPR: by recursing.

Note it needs to fold back the result to the correct type
(like negate_expr does).  Most easily by making fold_negate_expr
a wrapper around fold_negate_expr_1 and stripping/restoring the nop in
the wrapper.

Not sure if we had it at some point.  My oldest source is GCC 4.3
and it behaves the same way.

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