Calculating the number of the LLVM instructions in a function - llvm

Question

I have been using
opt -stats -analyze -instcount file.bc
to get statistic info of code. Now I would like to get the number of the LLVM instructions in a function of a particular name, say, "bar".
Ideally, I would expect an option of opt, which would work in this way
opt -stats -analyze -instcount funcname="bar"
What would be the right option to use? I googled a lot and have not got an answer yet.

Answer 1

Create a function analysis pass. (llvm::FunctionPass documentation)
Your code would look something like this:
// This is a contrived example.
#include <iterator>
#include <string>
#include "llvm/Pass.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instruction.h"
#include "llvm/Support/raw_ostream.h"
namespace
{
using namespace llvm;
cl::opt<std::string> functionName("funcname", cl::ValueRequired,
cl::desc("Function name"), cl::NotHidden);
class FunctionInstCounter : public FunctionPass
{
public:
static char ID;
FunctionInstCounter()
: FunctionPass(ID)
{
initializeFunctionInstCounterPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function& func) override
{
if (func.getName() != functionName)
{
return false;
}
unsigned int instCount = 0;
for (BasicBlock& bb : func)
{
instCount += std::distance(bb.begin(), bb.end());
}
llvm::outs() << "Number of instructions in " << func.getName() << ": "
<< instCount << "\n";
return false;
}
};
} // namespace
char FunctionInstCounter::ID = 0;
INITIALIZE_PASS(FunctionInstCounter, "funcinstcount",
"Function instruction counter", false, true)
llvm::Pass* llvm::createFunctionInstCounterPass()
{
return new FunctionInstCounter();
}
You would call it like this:
opt -funcinstcount -funcname=NameOfFunctionHere

Answer 2

bool runOnFunction(Function &F) override {
outs() << "No of Instructions : " <<F.getInstructionCount() << "\n";
}
I guess the above snippet is sufficient for finding the no of instructions in a function