On Thu, Dec 01, 2016 at 08:26:47AM +0100, Jakub Jelinek wrote:
> Isn't this too simplistic?  I mean, if you have say dirtype of signed char
> and argmin say 4096 + 32 and argmax say 4096 + 64, (signed char) arg
> has range 32, 64, while I think your routine will yield -128, 127 (well,
> 0 as min and -128 as max as that is what you return for signed type).
> Can't you subtract argmax - argmin (best just in wide_int, no need to build
> trees), and use what you have just for the case where that number doesn't
> fit into the narrower precision, otherwise if argmin - (dirtype) argmin
> == argmax - (dirtype) argmax, just use (dirtype) argmin and (dirtype) argmax
> as the range, and in case that it crosses a boundary figure if you can do
> anything than the above?  Guess all cases of signed/unsigned dirtype and/or
> argtype need to be considered.

Richard noted that you could have a look at CONVERT_EXPR_CODE_P
handling in extract_range_from_unary_expr.  I think it is the
              || (vr0.type == VR_RANGE
                  && integer_zerop (int_const_binop (RSHIFT_EXPR,
                       int_const_binop (MINUS_EXPR, vr0.max, vr0.min),
                         size_int (TYPE_PRECISION (outer_type)))))))
part that is important here for the narrowing conversion.


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