[C++] Alias analysis failure on pointer to local variable

Assigning to a local variable though a pointer appears to defeat the taint tracking. In the following example I would have expected to see a taint flow from line 16 to 17 but only the one from line 19 to 20 is reported. The taint seems to not propagate through the pointer correctly.

```cpp
int source()
{
return 2;
}

int target(int source)
{
return source;
}
int main(int argv, char **argc)
{
int a;
int *c = &a;
*c = source();
target(a); // not detected as reached

a = source();
target(a); // detected as reached

return 0;
}
```

This is the query I ran.

```ql
import cpp
import semmle.code.cpp.dataflow.new.TaintTracking

module SourceSinkCallConfig implements DataFlow::ConfigSig {
predicate isSource(DataFlow::Node source) {
source.asExpr().(Call).getTarget().getName() = "source"
}

predicate isSink(DataFlow::Node sink) {
exists(Call call |
call.getTarget().getName() = "target" and
call.getArgument(0) = sink.asExpr()
)
}
}

module SourceSinkCallTaint = TaintTracking::Global;

from DataFlow::Node source, DataFlow::Node sink, int source_line, int sink_line
where
SourceSinkCallTaint::flow(source, sink) and
source_line = source.getLocation().getStartLine() and
sink_line = sink.getLocation().getStartLine()
select source, source_line, sink, sink_line
```

This is the output I received.

```
| source | source_line | sink | sink_line |
+----------------+-------------+------+-----------+
| call to source | 19 | a | 20 |
```

CodeQL version: 2.19.3

Commencez par exécuter le reproducer C++ fourni et la requête SourceSinkCallTaint avec CodeQL 2.19.3, puis retracez le comportement du suivi de taint en C++ pour les écritures via des pointeurs et les variables locales. Le travail est terminé lorsque le flux de la ligne 16 vers la ligne 17 est signalé en même temps que le flux existant de la ligne 19 vers la ligne 20.

Rédigé par le modèle d'indexation à partir du texte de l'issue.