InnerLoopFinder.cc

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/*
    Copyright (c) 2002-2020 Tampere University.
 
    This file is part of TTA-Based Codesign Environment (TCE).
 
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
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    the rights to use, copy, modify, merge, publish, distribute, sublicense,
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    Software is furnished to do so, subject to the following conditions:
 
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
 
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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/**
 * @file InnerLoopFinder.cc
 *
 * LLVM pass for finding inner loops in the code.
 *
 * @author 2008-2015 Pekka Jääskeläinen
 */
 
#include <sstream>
#include <fstream>
#include <string>
#include <map>
 
#include "tce_config.h"
 
#include "CompilerWarnings.hh"
IGNORE_COMPILER_WARNING("-Wunused-parameter")
IGNORE_COMPILER_WARNING("-Wcomment")
 
#include <llvm/Analysis/LoopPass.h>
#include <llvm/Analysis/ScalarEvolution.h>
#include <llvm/Support/CommandLine.h>
 
#include "tce_config.h"
 
#include <llvm/IR/Module.h>
#include <llvm/IR/Constants.h>
#include <llvm/Analysis/LoopInfo.h>
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils.h"
#include <llvm/Pass.h>
#include "llvm/CodeGen/Passes.h"
#include "InnerLoopFinder.hh"
 
#include "llvm/InitializePasses.h"
 
using namespace llvm;
 
static llvm::cl::opt<bool>
DumpLoopInfo
("dump-loop-info", llvm::cl::init(false), llvm::cl::Hidden,
 llvm::cl::desc("Dump information about loops to files named [modulename].loopinfo.txt."));
 
static llvm::RegisterPass</*TCE::*/InnerLoopFinder> X(
    "find-innerloops-test", 
  "Finds inner loops test.", false, true);
 
INITIALIZE_PASS_BEGIN(
    InnerLoopFinder, "find-innerloops", 
    "Finds info of the inner loops in the program.",
    false, true)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LCSSAWrapperPass)
INITIALIZE_PASS_END(
    InnerLoopFinder, "find-innerloops", 
    "Finds info of the inner loops in the program.",
    false, true)
 
// Publically exposed interface to pass...
//const llvm::PassInfo* InnerLoopFinderID = X.getPassInfo();
 
// this causes duplicate TCE namespaces , both global and
// llvm::TCE which break plugin build, so this taken out from
// tce namespace to avoid having it
//namespace TCE {
 
char InnerLoopFinder::ID = 0;
 
InnerLoopFinder::InnerLoopFinder() : 
    LoopPass(ID) {
    dump = DumpLoopInfo;
}
 
void
InnerLoopFinder::getAnalysisUsage(llvm::AnalysisUsage &AU) const {
    AU.setPreservesCFG();
    AU.addRequiredID(llvm::LoopSimplifyID);
    AU.addRequiredID(llvm::LCSSAID);
    AU.addPreservedID(llvm::LCSSAID);
    AU.addRequired<llvm::LoopInfoWrapperPass>();
    AU.addRequired<llvm::ScalarEvolutionWrapperPass>();
    AU.addPreserved<llvm::LoopInfoWrapperPass>();
    AU.addPreserved<llvm::ScalarEvolutionWrapperPass>();
}
 
InnerLoopFinder::~InnerLoopFinder() {
    // flush and close all loop info dump files
    if (dump) {
        for (DumpFileIndex::iterator i = dumpFiles.begin(); 
             i != dumpFiles.end(); ++i) {
            std::ostream* stream = (*i).second;
            stream->flush();
            delete stream;
        }
        dumpFiles.clear();
    }
}
 
/**
 * Returns a stream to dump the loop info to.
 */
std::ostream&
InnerLoopFinder::out(llvm::Loop* l) {
 
    assert(l != NULL);
    
    std::string moduleName = 
        l->getHeader()->getParent()->getParent()->getModuleIdentifier();
    std::string fName = moduleName + ".loopinfo.txt";
    if (moduleName == "<stdin>") {
        fName = "loopinfo.txt";
    }
 
    if (dumpFiles.find(moduleName) == dumpFiles.end()) {
        std::fstream* outStream = 
            new std::fstream(
                fName.c_str(),
                std::ios_base::out | std::ios_base::trunc);
        dumpFiles[moduleName] = outStream;
    }
    return *dumpFiles[moduleName];
}
 
/**
 * Returns a textual description for the given loop.
 */
std::string
InnerLoopFinder::loopDescription(llvm::Loop* l) {
 
    if (l == NULL)
        return "[none]";
 
    std::ostringstream ss;
    assert(l->getHeader() != NULL);
    assert(l->getHeader()->getParent() != NULL);
    std::string curProcName = l->getHeader()->getParent()->getName().str();
    ss << "in " << curProcName << "()";
 
    return ss.str();
}
 
/**
 * Saves trip counts of single basic block inner loops.
 */
bool
InnerLoopFinder::runOnLoop(llvm::Loop* l, llvm::LPPassManager&) {
 
    const std::vector<llvm::Loop*>& subLoops = l->getSubLoops();
 
    unsigned subLoopCount = subLoops.size();
    unsigned tripCount = getSmallConstantTripCount(l);
    unsigned bbCount = l->getBlocks().size();
 
 
    /// early exits?
    llvm::SmallVector<llvm::BasicBlock*, 10> exitingBlocks;
 
#if 0
    /*
      This caused an LLVM crash in test cases
      llvm-frontend/tests/{FloatEmulationTest,NewLib,softloat_lowering,HelloWorld}:
 
      /home/visit0r/src/llvm-2.3/include/llvm/Support/Casting.h:199: 
      typename llvm::cast_retty<To, From>::ret_type llvm::cast(const Y&) 
      [with X = llvm::BasicBlock, Y = llvm::Value*]: 
      Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.      
     */
    l->getExitingBlocks(exitingBlocks);
    unsigned exitingBlockCount = exitingBlocks.size();
#endif
 
    unsigned callCount = 0;
    if (subLoopCount == 0) {
    for (llvm::LoopBase<llvm::BasicBlock, llvm::Loop>::
         block_iterator bb = 
                 l->block_begin(); bb != l->block_end(); ++bb) {
            llvm::BasicBlock& basicBlock = **bb;
            for (llvm::BasicBlock::iterator i = basicBlock.begin();  
                 i != basicBlock.end(); ++i) {
                llvm::Instruction& instruction = *i;
                if (instruction.getOpcode() == llvm::Instruction::Call)
                    ++callCount;
            }
        }
    }
 
    const bool innerLoop = 
        bbCount == 1 && subLoopCount == 0 && callCount == 0;
 
    if (innerLoop) {
        if (dump && tripCount > 0) {
            out(l) << "found an inner loop with trip count " 
                   << tripCount << std::endl;
        }
        assert(l->getBlocks().size() > 0);
 
        InnerLoopInfo loopInfo(tripCount);
        loopInfos_[l->getBlocks()[0]] = loopInfo;
    } 
 
    if (dump) {
        out(l) << "loop: " << loopDescription(l) << std::endl
               << "depth: " << l->getLoopDepth() << std::endl;
        out(l) << "sub loops: " << subLoopCount << std::endl;
        out(l) << "trip count: "; 
        if (tripCount != 0) {
            out(l) << "constant: " << tripCount;
        } else {
            out(l) << "unknown ";
        }
        out(l) << std::endl;
        out(l) << "basic blocks: " << bbCount << std::endl;
//        out(l) << "exiting blocks: " << exitingBlocks.size() << std::endl;
        if (subLoopCount == 0)
            out(l) << "calls: " << callCount << std::endl;
        out(l) << std::endl;
    }
    return false; // loop not modified
}
 
/**
 * Returns the trip count of the loop as a normal unsigned value, if 
 * possible. 
 *
 * Forwardported from LLVM 2.4. Returns 0 if the trip count is unknown
 * or not constant. Will also return 0 if the trip count is very large 
 * (>= 2^32).
 */
unsigned 
InnerLoopFinder::getSmallConstantTripCount(llvm::Loop* loop) {
    ScalarEvolution *SE =
        &getAnalysis<llvm::ScalarEvolutionWrapperPass>().getSE();
    llvm::BasicBlock* loopLatch = loop->getLoopLatch();
    // In case of the forever loop in the exit() the latch does
    // not jump out of the loop and SE cannot analyze the trip count,
    // which is infinite in that case.
    if (loopLatch == NULL || !loop->isLoopExiting(loopLatch))
        return 0;
    return SE->getSmallConstantTripCount(loop, loopLatch);
}