https://bugs.llvm.org/show_bug.cgi?id=50190
Bug ID: 50190
Summary: Possible Issue with Whole Program Devirtualization
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected],
[email protected]
class A {
public:
virtual int foo() const = 0;
};
class B : public A {
public:
virtual int foo() const { return 2; }
};
class C : public A {
public:
virtual int foo() const { return 3; }
};
A *get_A(int num) {
if (num > 1) {
printf("returning new B\n");
return new B;
}
printf("returning new C\n");
return new C;
}
__attribute__((noinline))
void call_foo(int argc) {
C *c = (C *)get_A(argc);
printf("%d\n", c->foo());
}
int main(int argc, char *argv[]) {
call_foo(argc);
}
trunk clang with -O3 -flto -whole-program-vtables -fvisibility=hidden outputs
./a.out 1
returning new B
3
gcc 10.2 with -O3 -flto -fwhole-program -fvisibility=hidden outputs
./a.out 1
returning new B
2
It looks like the c->foo is being devirtualized to a direct C::foo() call.
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