LLVM LoopInfo in FunctionPass doesn't compile - llvm

Question

i'm starting to learn llvm api and i wrote my first pass.
My goal is to print how functions call each others.
Lately i wanted to add some loop information to the display to look if a function can be call several time or not. But when i try to use LoopInfo i got this compilation error :
llvm[0]: Compiling cfg.cpp for Debug+Asserts build (PIC)
In file included from cfg.cpp:19:
In file included from /home/llvm-lab/llvm/include/llvm/Pass.h:378:
/home/llvm-lab/llvm/include/llvm/PassAnalysisSupport.h:56:37: error:
no member named 'ID' in 'llvm::LoopInfo'
return addRequiredID(PassClass::ID);
^
cfg.cpp:33:10: note: in instantiation of function template
specialization 'llvm::AnalysisUsage::addRequired<llvm::LoopInfo>'
requested here
AU.addRequired<LoopInfo>();
^
1 error generated.
Here is my code :
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"
#include "iostream"
#include "llvm/Pass.h"
#include "llvm/IR/InstIterator.h"
#include <llvm/IR/Instructions.h>
#include <llvm/Analysis/LoopInfo.h>
using namespace llvm;
namespace {
struct CFG : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
CFG() : FunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LoopInfo>();
}
bool runOnFunction(Function &F) override {
errs().write_escaped(F.getName());
errs() << " : ";
for( Function::iterator b = F.begin() , be = F.end(); b != be; ++b){
errs() << "\n\t BB : ";
LoopInfo *loop = new LoopInfo();
bool isLoop = loop->getLoopFor(b);
if(isLoop){
errs() << "loop{";
}
for(BasicBlock::iterator i = b->begin() , ie = b->end(); i!=ie; ++i){
if( isa<CallInst>(&(*i)) || isa<InvokeInst>(&(*i))){
errs() << cast<CallInst>(&(*i))->getCalledFunction()->getName() << "\t";
}
}
if(isLoop){
errs() << "}";
}
}
errs() << '\n';
return false;
}
};
}
char CFG::ID = 0;
static RegisterPass<CFG> X("CFG", "Gen CFG",true ,true);
I can't find any reference to an "no member named 'ID' in 'llvm::LoopInfo'" error anywhere, does anyone have an idea about what's is wrong here ?

Answer 1

Why your code could not be build
AU.addRequired<typename passclass>() need a type of LLMV::Pass, however what you pass in is LoopInfo, which is just an LLVM internal class for loop information maintenance. It does not has a field ID.
LoopInfoWrapperPass should be used instead
If you want to get the loop information. Try to change it to AU.addRequired<LoopInfoWrapperPass> as shown in the LLVM Write a new Pass document. LoopInfoWrapperPass is used to generate LoopInfo.
LoopInfo should be get from the pass
There is also a problem in your code about how to get the LoopInfo, you are trying to use new to create a LoopInfo, what you get will be an empty LoopInfo.
The "should work" code for your question
Following is a modified version of your code, which could printout expected informations.
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"
#include "iostream"
#include "llvm/Pass.h"
#include "llvm/IR/InstIterator.h"
#include <llvm/IR/Instructions.h>
#include <llvm/Analysis/LoopInfo.h>
using namespace llvm;
namespace {
struct CFG : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
CFG() : FunctionPass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
AU.addRequired<LoopInfoWrapperPass>();
}
bool runOnFunction(Function &F) override {
LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
errs().write_escaped(F.getName());
errs() << " : ";
for( Function::iterator b = F.begin() , be = F.end(); b != be; ++b){
errs() << "\n\t BB : ";
bool isLoop = LI.getLoopFor(b);
if(isLoop){
errs() << "loop{";
}
for(BasicBlock::iterator i = b->begin() , ie = b->end(); i!=ie; ++i){
if( isa<CallInst>(&(*i)) || isa<InvokeInst>(&(*i))){
errs() << cast<CallInst>(&(*i))->getCalledFunction()->getName() << "\t";
}
}
if(isLoop){
errs() << "}";
}
}
errs() << '\n';
return false;
}
};
}
char CFG::ID = 0;
static RegisterPass<CFG> X("CFG", "Gen CFG",true ,true);
For the following code feed to LLVM opt:
#include <stdio.h>
#define ARRAY_SIZE 100
int foo(int* a , int n) {
int i;
int sum = 0;
for (; i < n; i++) {
sum += a[i];
}
return sum;
}
int main() {
int a[ARRAY_SIZE] = {1};
int sum = foo(a, ARRAY_SIZE);
printf("sum:0x%x\n", sum);
return 0;
}
The output will be:
foo :
BB :
BB : loop{}
BB : loop{}
BB : loop{}
BB :
main :
BB : llvm.memset.p0i8.i64 foo printf