https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87634
Bug ID: 87634
Summary: CSE for dynamic_cast
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Simon.Richter at hogyros dot de
Target Milestone: ---
With the code
struct A { virtual void foo() = 0; };
struct B : A { virtual void foo() {} void bar() const; };
void test(A *a)
{
if(auto b = dynamic_cast<B *>(a))
b->bar();
if(auto b = dynamic_cast<B *>(a))
b->bar();
}
I'd expect the type of the object to be unchanged between the two
`dynamic_cast` invocations, so the second type check would be unnecessary. The
generated code does two checks, however.
It is in theory possible to replace the object in-place with one of different
type if it is also accessible through a global pointer from within `B::bar()`,
but is this a good enough reason to repeat the type check, or would it be
possible to optimize out the second dynamic_cast<> here?
