https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96988
Bug ID: 96988
Summary: Bad/missing warnings when returning a temporary from
an inlined function
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: blubban at gmail dot com
Target Milestone: ---
Minimal testcase:
// compile with: gcc -O2 -Wall bug.cpp
static int * foo()
{
int a = 42;
int * b = &a;
return b;
}
int bar()
{
return *foo();
}
Result: A misleading warning in wrong function.
<source>: In function 'bar':
<source>:10:12: warning: 'a' is used uninitialized in this function
[-Wuninitialized]
10 | return *foo();
| ^~~~~~
Expected result: I get a good warning (but the misleading one too) if the buggy
function is not inline, static, or a C++ template.
<source>: In function 'foo':
<source>:5:12: warning: function returns address of local variable
[-Wreturn-local-addr]
5 | return b;
| ^
<source>:3:9: note: declared here
3 | int a = 42;
| ^
More realistic example:
// compile with: g++ -O3 -Wall bug.cpp
template<typename T>
const T& max(const T& a) { return a; }
template<typename T, typename... Args>
const T& max(const T& a, Args... args)
{
// whoops, this creates temporaries with insufficient lifetime if the
arguments aren't same type
const T& b = max(args...);
if (a < b) return b;
else return a;
}
int victim()
{
return max(1, 2u);
}
(I'm not sure what component this belongs to; please recategorize if wrong.)
