LLVM pass to count vector type instructions - c++

Question

I am trying to write an LLVM pass that counts instructions of vector type.
for instructions like :
%24 = or <2 x i64> %21, %23
%25 = bitcast <16 x i8> %12 to <8 x i16>
%26 = shl <8 x i16> %25, <i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1, i16 1>
%27 = bitcast <8 x i16> %26 to <2 x i64>
I wrote this code:
for (auto &F : M) {
for (auto &B : F) {
for (auto &I : B) {
if (auto* VI = dyn_cast<InsertElementInst>(&I)) {
Value* op = VI->getOperand(0);
if (op->getType()->isVectorTy()){
++vcount;
}
}
But for some reason if (auto* VI = dyn_cast<InsertElementInst>(&I)) is never satisfied.
Any idea why?
Thanks in advance.

Answer 1

InsertElementInst is one specific instruction (that inserts an element into a vector) - and there is none in your list of instructiokns.
You probably want to dyn_cast to a regular use the Instruction in I as it is.
[I personally would use a one of the function or module pass classes as a base, so you only need to implement the inner loops of your code, but that's more of a "it's how you're supposed to do things", not something you HAVE to do to make it work].

Answer 2

In LLVM, the instruction is the same as it's result. so for an example
%25 = bitcast <16 x i8> %12 to <8 x i16>
when you cast Instruction I to value you get %25
Value* psVal = cast<Value>(&I);
and then you can check if it is of vector type or not by getType()->isVectorTy().
Also i suggest you look at inheritance diagram of llvm Value for more clarification
here http://llvm.org/docs/doxygen/html/classllvm_1_1Value.html