How do I try to cast a Value* to a subclass?

Question

I have a list of Value* and some of them I know are PHINode*.

I could do dynamic_cast<PHINode*>(value) and check if it casted to see if it's a PHINode* but I vaguely recall there's a better way.

If you're certain that the pointer is a pointer to the subclass, then just do `static_cast(value)` and be done with it. — Some programmer dude, Apr 15 '15 at 23:58

score 1 · Accepted Answer · edited May 23 '17 at 10:24

After a lot of looking around, these two questions indirectly answered my question

llvm apparently has a built in type checking system. There's a reference page here. It works like this

if(isa<PHINode>(value)){
    PHINode* phi = cast<PHINode>(value);
}
if(PHINode* phi = dyn_cast<PHINode>(value)){//alternatively
    ...
}

And it does appear that you don't need to specify that it's a pointer, so it's not isa<PHINode*>

Finally, as it turns out, dynamic_cast will NOT work since they implement their own RTTI

The LLVM source-base makes extensive use of a custom form of RTTI. These templates have many similarities to the C++ dynamic_cast<> operator, but they don’t have some drawbacks (primarily stemming from the fact that dynamic_cast<> only works on classes that have a v-table).

Exactly how is this better than the `dynamic_cast` method? Most likely, the `isa` function uses `dynamic_cast` anyway. — Some programmer dude, Apr 15 '15 at 23:59
LLVM uses its own typing mechanism that doesn't use the normal c++ vtables. dynamic_cast won't work since these classes aren't c++ polymorphic — Colin LeMahieu, Apr 16 '15 at 03:23

How do I try to cast a Value* to a subclass?

1 Answers1