Hello,
I am writing an optimization pass which optimizes code based on an online
pointer analysis algorithm and need to detect pointers which are pointing to
derived types. I have not had any problem identifying pointers in general
using isa<PointerType>(...), but I can't seem to figure out how I can make
sure that the pointer is pointing to a scalar value and not a function,
array, struct, etc.
What am I missing?
http://llvm.org/docs/doxygen/html/classllvm_1_1SequentialType.html#633173cae0cf68e70a7dcc33d3e3ceb8
— Gordon
Zappel-Phillip wrote:
Hello,
I am writing an optimization pass which optimizes code based on an online
pointer analysis algorithm and need to detect pointers which are pointing to
derived types. I have not had any problem identifying pointers in general
using isa<PointerType>(...), but I can't seem to figure out how I can make
sure that the pointer is pointing to a scalar value and not a function,
array, struct, etc.What am I missing?
Please see the doxygen: http://llvm.org/doxygen/classllvm_1_1Type.html
if (const PointerType *PTy = dyn_cast<PointerType>(...)) {
const Type *InnerTy = PTy->getElementType();
switch (InnerTy->getTypeID()) {
case Type::ArrayTyID:
...
case Type::FunctionTyID:
...
case Type::StructTyID:
...
case Type::IntegerTyID:
...
}
}
A switch on getTypeID() is equivalent to isa<>, but more efficient than a chain of if's when doing multiple tests.
If you only care about whether it's first class or not, you can just call InnerTy->isFirstClass().
Nick Lewycky
I believe I failed to ask the question properly, I am not trying to determine
whether the elements of an array are scalar type. Instead, I want to be able
to iterate over the function's parameters and determine whether a pointer
argument is actually an array being passed which contains scalar values, or
simply a pointer with a single scalar value. In other words, I want to
ignore functions that accept arrays as arguments.
Nick Lewycky wrote:
If I'm following correctly, you want to distinguish between "int
a(char* x)" and "int a(char x)"? That's impossible purely looking
at types; C itself doesn't distinguish between them.
One somewhat effective approach would be to look at the users of the
argument; if the argument only gets used directly by load and store
instructions (i.e. the function never manipulates or stores away the
pointer), the function is treating it as a pointer. In general,
though, it's impossible to distinguish the two cases.
-Eli