path: root/lib/Analysis/ConstantFolding.cpp

//===-- ConstantFolding.cpp - Fold instructions into constants ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines routines for folding instructions into constants.
//
// Also, to supplement the basic VMCore ConstantExpr simplifications,
// this file defines some additional folding routines that can make use of
// TargetData information. These functions cannot go in VMCore due to library
// dependency issues.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
#include <cerrno>
#include <cmath>
using namespace llvm;

//===----------------------------------------------------------------------===//
// Constant Folding internal helper functions
//===----------------------------------------------------------------------===//

/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with 
/// TargetData.  This always returns a non-null constant, but it may be a
/// ConstantExpr if unfoldable.
static Constant *FoldBitCast(Constant *C, const Type *DestTy,
                             const TargetData &TD) {
  
  // This only handles casts to vectors currently.
  const VectorType *DestVTy = dyn_cast<VectorType>(DestTy);
  if (DestVTy == 0)
    return ConstantExpr::getBitCast(C, DestTy);
  
  // If this is a scalar -> vector cast, convert the input into a <1 x scalar>
  // vector so the code below can handle it uniformly.
  if (isa<ConstantFP>(C) || isa<ConstantInt>(C)) {
    Constant *Ops = C; // don't take the address of C!
    return FoldBitCast(ConstantVector::get(&Ops, 1), DestTy, TD);
  }
  
  // If this is a bitcast from constant vector -> vector, fold it.
  ConstantVector *CV = dyn_cast<ConstantVector>(C);
  if (CV == 0)
    return ConstantExpr::getBitCast(C, DestTy);
  
  // If the element types match, VMCore can fold it.
  unsigned NumDstElt = DestVTy->getNumElements();
  unsigned NumSrcElt = CV->getNumOperands();
  if (NumDstElt == NumSrcElt)
    return ConstantExpr::getBitCast(C, DestTy);
  
  const Type *SrcEltTy = CV->getType()->getElementType();
  const Type *DstEltTy = DestVTy->getElementType();
  
  // Otherwise, we're changing the number of elements in a vector, which 
  // requires endianness information to do the right thing.  For example,
  //    bitcast (<2 x