Question about fold C_MAYBE_CONST_EXPR expressions

["Bin.Cheng" <amker dot cheng at gmail dot com>]

Hi,
I ran into a problem that C frontend (in function
build_conditional_expr) creates expression like (C_MAYBE_CONST_EXPR
(NULL, x + const)).  The inner expression (and its operands) have
unsigned int type.  After that, the expression needs to be casted to
result type which is unsigned short.  In this case,
convert_to_integer/convert_to_integer_1 doesn't fold into
C_MAYBE_CONST_EXPR and just returns (unsigned
short)(C_MAYBE_CONST_EXPR (NULL, x + const)), as a result, (unsigned
short)(x + const) won't be simplified as (unsigned short)x + const.
My questions are, 1) Is it possible to fold type conversion into
C_MAYBE_CONST_EXPR's inner expression in convert_to_integer_1?  2) If
not, looks like there are couple of places the mentioned fold can be
done, for example, after stripping C_MAYBE_CONST_EXPR and before (or
during) gimplify.  So which place is preferred?

Thanks,
bin