FreeChainXenon/gcc
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

c++: error with bit-fields and scoped enums [PR111895]

Browse source 
Here we issue a bogus error: invalid operands of types 'unsigned char:2'
and 'int' to binary 'operator!=' when casting a bit-field of scoped enum
type to bool.

In build_static_cast_1, perform_direct_initialization_if_possible returns
NULL_TREE, because the invented declaration T t(e) fails, which is
correct.  So we go down to ocp_convert, which has code to deal with this
case:
          /* We can't implicitly convert a scoped enum to bool, so convert
             to the underlying type first.  */
          if (SCOPED_ENUM_P (intype) && (convtype & CONV_STATIC))
            e = build_nop (ENUM_UNDERLYING_TYPE (intype), e);
but the SCOPED_ENUM_P is false since intype is <unnamed-unsigned:2>.
This could be fixed by using unlowered_expr_type.  But then
c_common_truthvalue_conversion/CASE_CONVERT has a similar problem, and
unlowered_expr_type is a C++-only function.

Rather than adding a dummy unlowered_expr_type to C, I think we should
follow [expr.static.cast]p3: "the lvalue-to-rvalue conversion is applied
to the bit-field and the resulting prvalue is used as the operand of the
static_cast."  There are no prvalue bit-fields, so the l-to-r conversion
performed in decay_conversion will get us an expression whose type is the
enum.

	PR c++/111895

gcc/cp/ChangeLog:

	* typeck.cc (build_static_cast_1): Call decay_conversion.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/scoped_enum12.C: New test.
This commit is contained in:
Marek Polacek 2023-10-23 17:06:45 -04:00
parent 444a485f8f
commit 6fa7284e28
2 changed files with 15 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
gcc/cp/typeck.cc
View file

@ -8405,6 +8405,13 @@ build_static_cast_1 (location_t loc, tree type, tree expr, bool c_cast_p,
return expr;
if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
expr = TREE_OPERAND (expr, 0);
/* [expr.static.cast]: "If the value is not a bit-field, the result
refers to the object or the specified base class subobject thereof;
otherwise, the lvalue-to-rvalue conversion is applied to the
bit-field and the resulting prvalue is used as the operand of the
static_cast." There are no prvalue bit-fields; the l-to-r conversion
will give us an object of the underlying type of the bit-field. */
expr = decay_conversion (expr, complain);
return ocp_convert (type, expr, CONV_C_CAST, LOOKUP_NORMAL, complain);
}

8
gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C Normal file
View file

@ -0,0 +1,8 @@
// PR c++/111895
// { dg-do compile { target c++11 } }
enum class o_field : unsigned char { no, yes, different_from_s };
struct fields {
o_field o : 2;
};
bool func(fields f) { return static_cast<bool>(f.o); }