https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101518
Bug ID: 101518
Summary: Invalid value in bit-field when setting underlying
data through reference
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: klimkin at gmail dot com
Target Milestone: ---
In the example below, GCC starting v10 seems to produce invalid code for
accessing a bit field when the value for the underlying memory is set through a
reference. Consider example:
struct BitFieldLayout {
using DataType = unsigned;
BitFieldLayout() { reinterpret_cast<DataType&>(*this) = {}; }
DataType& raw_ref() { return reinterpret_cast<DataType&>(*this); }
DataType a : 1;
};
class Ref {
public:
operator unsigned&() { return value; }
unsigned& value;
};
int f()
{
BitFieldLayout bfl;
Ref ref{bfl.raw_ref()};
ref.value = 1;
return bfl.a; // expected value is 1
}
g++ (Compiler-Explorer-Build) 11.1.0
f():
xor eax, eax
ret
g++ (Compiler-Explorer-Build-gcc--binutils-2.36.1) 9.4.0
f():
mov eax, 1
ret
clang version 12.0.1
f(): # @f()
mov eax, 1
ret
