https://bugs.llvm.org/show_bug.cgi?id=52194
Bug ID: 52194
Summary: Misleading error message in constexpr function when
variable is uninitialized
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++2b
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Minimal example:
constexpr int func(int a)
{
int sum;
sum += a;
return sum;
}
constexpr int val = func(4);
When I compile this on Godbolt using the "x86-64 clang (trunk)" branch and the
-std=c++20 flag I get the following error message:
<source>:7:15: error: constexpr variable 'val' must be initialized by a
constant expression
constexpr int val = func(4);
^ ~~~~~~~
<source>:4:6: note: subexpression not valid in a constant expression
sum += a;
^
<source>:7:21: note: in call to 'func(4)'
constexpr int val = func(4);
^
1 error generated.
This is misleading because the actual problem is that sum was not initialized.
If sum is initialized with sum=0 then there is no error. This problem exists
for other modify and assign operators as well. Using separate assignment and
equality operators does not have this problem. For example:
constexpr int func(int a)
{
int sum;
sum = sum + a;
return sum;
}
constexpr int val = func(4);
Give this error message:
<source>:7:15: error: constexpr variable 'val' must be initialized by a
constant expression
constexpr int val = func(4);
^ ~~~~~~~
<source>:4:8: note: read of uninitialized object is not allowed in a constant
expression
sum = sum + a;
^
<source>:7:21: note: in call to 'func(4)'
constexpr int val = func(4);
^
1 error generated.
Which correctly identifies that the problem is that sum is uninitialized.
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