DirectXShaderCompiler/lib/Analysis/VectorUtils2.cpp

//===----------- VectorUtils2.cpp - findScalarElement function -----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines vectorizer utility function findScalarElement.
// Splitting this function from VectorUtils.cpp into a separate file 
// makes dxilconv.dll 121kB smaller (x86 release, compiler optimization for size).
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Value.h"

/// \brief Given a vector and an element number, see if the scalar value is
/// already around as a register, for example if it were inserted then extracted
/// from the vector.
llvm::Value *llvm::findScalarElement(llvm::Value *V, unsigned EltNo) {
  assert(V->getType()->isVectorTy() && "Not looking at a vector?");
  VectorType *VTy = cast<VectorType>(V->getType());
  unsigned Width = VTy->getNumElements();
  if (EltNo >= Width)  // Out of range access.
    return UndefValue::get(VTy->getElementType());

  if (Constant *C = dyn_cast<Constant>(V))
    return C->getAggregateElement(EltNo);

  if (InsertElementInst *III = dyn_cast<InsertElementInst>(V)) {
    // If this is an insert to a variable element, we don't know what it is.
    if (!isa<ConstantInt>(III->getOperand(2)))
      return nullptr;
    unsigned IIElt = cast<ConstantInt>(III->getOperand(2))->getZExtValue();

    // If this is an insert to the element we are looking for, return the
    // inserted value.
    if (EltNo == IIElt)
      return III->getOperand(1);

    // Otherwise, the insertelement doesn't modify the value, recurse on its
    // vector input.
    return findScalarElement(III->getOperand(0), EltNo);
  }

  if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V)) {
    unsigned LHSWidth = SVI->getOperand(0)->getType()->getVectorNumElements();
    int InEl = SVI->getMaskValue(EltNo);
    if (InEl < 0)
      return UndefValue::get(VTy->getElementType());
    if (InEl < (int)LHSWidth)
      return findScalarElement(SVI->getOperand(0), InEl);
    return findScalarElement(SVI->getOperand(1), InEl - LHSWidth);
  }

  // Extract a value from a vector add operation with a constant zero.
  Value *Val = nullptr; Constant *Con = nullptr;
  if (match(V,
            llvm::PatternMatch::m_Add(llvm::PatternMatch::m_Value(Val),
                                      llvm::PatternMatch::m_Constant(Con)))) {
    if (Constant *Elt = Con->getAggregateElement(EltNo))
      if (Elt->isNullValue())
        return findScalarElement(Val, EltNo);
  }

  // Otherwise, we don't know.
  return nullptr;
}