fstrict-enums and value ranges in VRP

[kugan <kugan dot vivekanandarajah at linaro dot org>]

Hi All,

When I compile the following code with g++ using -fstrict-enums and -O2

enum v
{
  OK = 0,
  NOK = 1,
};

int foo0 (enum v a)
{
  if (a > NOK)
    return 0;
  return 1;
}

vrp1 dump looks like:
Value ranges after VRP:

a.0_1: VARYING
_2: [0, 1]
a_3(D): VARYING


int foo0(v) (v a)
{
  int a.0_1;
  int _2;

  <bb 2>:
  a.0_1 = (int) a_3(D);
  if (a.0_1 > 1)
    goto <bb 4>;
  else
    goto <bb 3>;

  <bb 3>:

  <bb 4>:
  # _2 = PHI <0(2), 1(3)>
  return _2;

}

Should we infer value ranges for the enum since this is -fstrict-enums 
and optimize it?

@item -fstrict-enums
@opindex fstrict-enums
Allow the compiler to optimize using the assumption that a value of
enumerated type can only be one of the values of the enumeration (as
defined in the C++ standard; basically, a value that can be
represented in the minimum number of bits needed to represent all the
enumerators).  This assumption may not be valid if the program uses a
cast to convert an arbitrary integer value to the enumerated type.


Thanks,
Kugan