[LLVMdev] "symbol lookup error" while running a Simple Loop Pass

[Arnamoy Bhattacharyya]

Problem solved.  I was building llvm in a separate llvm-build directory.  I
built it within the llvm-src directory (which kept all the llvm .so and my
pass' .so in the llvm-src/Release+Asserts/lib directory) to solve the
problem.

Can anyone tell me what's the difference between writing a pass as a
"struct" (as in the tutorial) and as a "class" (as most developers do)?

Thanks again;
---------- Forwarded message ----------
From: Arnamoy Bhattacharyya <arnamoy at ualberta.ca>
Date: Thu, Jul 5, 2012 at 12:34 AM
Subject: "symbol lookup error" while running a Simple Loop Pass
To: llvmdev at cs.uiuc.edu


Hello;

I wrote this simple loop pass to collect the number of instructions in each
loop of the program.  The code is as follows-

#define DEBUG_TYPE "loopinst"
#include "llvm/Pass.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/LoopInfo.h"

using namespace llvm;

STATISTIC(LoopInstNum, "Counts number of instructions in a loop");

namespace {
  struct LoopInst : public LoopPass {
    static char ID; // Pass identification, replacement for typeid
    LoopInst() : LoopPass(ID) {}

    virtual bool runOnLoop(Loop *L, LPPassManager &LPM) {
        LoopInfo *LI = &getAnalysis<LoopInfo>();
for (Loop::block_iterator b = L->block_begin(), be = L->block_end();b !=
be; ++b)
 {
for (BasicBlock::iterator i = (*b)->begin(), ie = (*b)->end(); i != ie; ++i)
 {
      ++LoopInstNum;
      errs() << "Hello: ";
 }
}

      return false;
    }

    // We don't modify the program, so we preserve all analyses
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addRequired<LoopInfo>();
      AU.addPreserved<LoopInfo>();
    }
  };
}

char LoopInst::ID = 0;
static RegisterPass<LoopInst> X("loop-inst", "loop instruction Pass");


I put it under llvm-src/lib/Transforms directory and ran a "make" from
there to create the .so file.  But when I run opt with the library, I get
the following error -

opt -load=/home/arnie/llvm-development/llvm/Debug+Asserts/lib/LoopInst.so
-loops -loop-inst a.s

opt: symbol lookup error:
/home/arnie/llvm-development/llvm/Debug+Asserts/lib/LoopInst.so: undefined
symbol: _ZNK4llvm8LoopBaseINS_10BasicBlockENS_4LoopEE11block_beginEv

Can anyone tell me what I am doing wrong?

Also what's the difference between declaring a pass as a struct vs
declaring it as a class.  In the "writing a pass" tutorial the "Hello" pass
has been declared as a struct but most (if not all) the LLVM passes are
written as classes.

Thanks a lot;
-- 
Arnamoy Bhattacharyya
Athabasca Hall 143
Department of Computing Science - University of Alberta
Edmonton, Alberta, Canada, T6G 2E8
587-710-7073



-- 
Arnamoy Bhattacharyya
Athabasca Hall 143
Department of Computing Science - University of Alberta
Edmonton, Alberta, Canada, T6G 2E8
587-710-7073
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