path: root/lib/Transforms/Utils/SimplifyLibCalls.cpp

//===------ SimplifyLibCalls.cpp - Library calls simplifier ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This is a utility pass used for testing the InstructionSimplify analysis.
// The analysis is applied to every instruction, and if it simplifies then the
// instruction is replaced by the simplification.  If you are looking for a pass
// that performs serious instruction folding, use the instcombine pass instead.
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/SimplifyLibCalls.h"
#include "llvm/DataLayout.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Function.h"
#include "llvm/IRBuilder.h"
#include "llvm/LLVMContext.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/BuildLibCalls.h"

using namespace llvm;

/// This class is the abstract base class for the set of optimizations that
/// corresponds to one library call.
namespace {
class LibCallOptimization {
protected:
  Function *Caller;
  const DataLayout *TD;
  const TargetLibraryInfo *TLI;
  const LibCallSimplifier *LCS;
  LLVMContext* Context;
public:
  LibCallOptimization() { }
  virtual ~LibCallOptimization() {}

  /// callOptimizer - This pure virtual method is implemented by base classes to
  /// do various optimizations.  If this returns null then no transformation was
  /// performed.  If it returns CI, then it transformed the call and CI is to be
  /// deleted.  If it returns something else, replace CI with the new value and
  /// delete CI.
  virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B)
    =0;

  Value *optimizeCall(CallInst *CI, const DataLayout *TD,
                      const TargetLibraryInfo *TLI,
                      const LibCallSimplifier *LCS, IRBuilder<> &B) {
    Caller = CI->getParent()->getParent();
    this->TD = TD;
    this->TLI = TLI;
    this->LCS = LCS;
    if (CI->getCalledFunction())
      Context = &CI->getCalledFunction()->getContext();

    // We never change the calling convention.
    if (CI->getCallingConv() != llvm::CallingConv::C)
      return NULL;

    return callOptimizer(CI->getCalledFunction(), CI, B);
  }
};

//===----------------------------------------------------------------------===//
// Helper Functions
//===----------------------------------------------------------------------===//

/// isOnlyUsedInZeroEqualityComparison - Return true if it only matters that the
/// value is equal or not-equal to zero.
static bool isOnlyUsedInZeroEqualityComparison(Value *V) {
  for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
       UI != E; ++UI) {
    if (ICmpInst *IC = dyn_cast<ICmpInst>(*UI))
      if (IC->isEquality())
        if (Constant *C = dyn_cast<Constant>(IC->getOperand(1)))
          if (C->isNullValue())
            continue;
    // Unknown instruction.
    return false;
  }
  return true;
}

//===----------------------------------------------------------------------===//
// Fortified Library Call Optimizations
//===----------------------------------------------------------------------===//

struct FortifiedLibCallOptimization : public LibCallOptimization {
protected:
  virtual bool isFoldable(unsigned SizeCIOp, unsigned SizeArgOp,
			  bool isString) const = 0;
};

struct InstFortifiedLibCallOptimization : public FortifiedLibCallOptimization {
  CallInst *CI;

  bool isFoldable(unsigned SizeCIOp, unsigned SizeArgOp, bool isString) const {
    if (CI->getArgOperand(SizeCIOp) == CI->getArgOperand(SizeArgOp))
      return true;
    if (ConstantInt *SizeCI =
                           dyn_cast<ConstantInt>(CI->getArgOperand(SizeCIOp))) {
      if (SizeCI->isAllOnesValue())
        return true;
      if (isString) {
        uint64_t Len = GetStringLength(CI->getArgOperand(SizeArgOp));
        // If the length is 0 we don't know how long it is and so we can't
        // remove the check.
        if (Len == 0) return false;
        return SizeCI->getZExtValue() >= Len;
      }
      if (ConstantInt *Arg = dyn_cast<ConstantInt>(
                                                  CI->getArgOperand(SizeArgOp)))
        return SizeCI->getZExtValue() >= Arg->getZExtValue();
    }
    return false;
  }
};

struct MemCpyChkOpt : public InstFortifiedLibCallOptimization {
  virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
    this->CI = CI;
    FunctionType *FT = Callee->getFunctionType();
    LLVMContext &Context = CI->getParent()->getContext();

    // Check if this has the right signature.
    if (FT->getNumParams() != 4 || FT->getReturnType() !=