From 6fa7284e2824310bb7204d41b5243c677ecb62d3 Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Mon, 23 Oct 2023 17:06:45 -0400
Subject: [PATCH] c++: error with bit-fields and scoped enums [PR111895]
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.
---
gcc/cp/typeck.cc | 7 +++++++
gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C | 8 ++++++++
2 files changed, 15 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index f3dc80c40cfa..3b719326d76c 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -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);
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C b/gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C
new file mode 100644
index 000000000000..1d10431e6dc4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/scoped_enum12.C
@@ -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); }
--
GitLab