path: root/lib/Transforms/Scalar/CodeGenPrepare.cpp

//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass munges the code in the input function to better prepare it for
// SelectionDAG-based code generation. This works around limitations in it's
// basic-block-at-a-time approach. It should eventually be removed.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "codegenprepare"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/InlineAsm.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Utils/AddrModeMatcher.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BuildLibCalls.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/ValueHandle.h"
using namespace llvm;
using namespace llvm::PatternMatch;

STATISTIC(NumBlocksElim, "Number of blocks eliminated");
STATISTIC(NumPHIsElim,   "Number of trivial PHIs eliminated");
STATISTIC(NumGEPsElim,   "Number of GEPs converted to casts");
STATISTIC(NumCmpUses, "Number of uses of Cmp expressions replaced with uses of "
                      "sunken Cmps");
STATISTIC(NumCastUses, "Number of uses of Cast expressions replaced with uses "
                       "of sunken Casts");
STATISTIC(NumMemoryInsts, "Number of memory instructions whose address "
                          "computations were sunk");
STATISTIC(NumExtsMoved,  "Number of [s|z]ext instructions combined with loads");
STATISTIC(NumExtUses,    "Number of uses of [s|z]ext instructions optimized");
STATISTIC(NumRetsDup,    "Number of return instructions duplicated");

namespace {
  class CodeGenPrepare : public FunctionPass {
    /// TLI - Keep a pointer of a TargetLowering to consult for determining
    /// transformation profitability.
    const TargetLowering *TLI;
    DominatorTree *DT;
    ProfileInfo *PFI;
    
    /// CurInstIterator - As we scan instructions optimizing them, this is the
    /// next instruction to optimize.  Xforms that can invalidate this should
    /// update it.
    BasicBlock::iterator CurInstIterator;

    /// Keeps track of non-local addresses that have been sunk into a block.
    /// This allows us to avoid inserting duplicate code for blocks with
    /// multiple load/stores of the same address.
    DenseMap<Value*, Value*> SunkAddrs;

    /// UpdateDT - If CFG is modified in anyway, dominator tree may need to
    /// be updated.
    bool UpdateDT;

  public:
    static char ID; // Pass identification, replacement for typeid
    explicit CodeGenPrepare(const TargetLowering *tli = 0)
      : FunctionPass(ID), TLI(tli) {
        initializeCodeGenPreparePass(*PassRegistry::getPassRegistry());
      }
    bool runOnFunction(Function &F);

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.addPreserved<DominatorTree>();
      AU.addPreserved<ProfileInfo>();
    }

  private:
    bool EliminateMostlyEmptyBlocks(Function &F);
    bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
    void EliminateMostlyEmptyBlock(BasicBlock *BB);
    bool OptimizeBlock(BasicBlock &BB);
    bool OptimizeInst(Instruction *I);
    bool OptimizeMemoryInst(Instruction *I, Value *Addr, const Type *AccessTy);
    bool OptimizeInlineAsmInst(CallInst *CS);
    bool OptimizeCallInst(CallInst *CI);
    bool MoveExtToFormExtLoad(Instruction *I);
    bool OptimizeExtUses(Instruction *I);
    bool DupRetToEnableTailCallOpts(ReturnInst *RI);
  };
}

char CodeGenPrepare::ID = 0;
INITIALIZE_PASS(CodeGenPrepare, "codegenprepare",
                "Optimize for code generation",