path: root/lib/Transforms/InstCombine/InstCombineSelect.cpp

//===- InstCombineSelect.cpp ----------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitSelect function.
//
//===----------------------------------------------------------------------===//

#include "InstCombine.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
using namespace llvm;
using namespace PatternMatch;

/// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
/// returning the kind and providing the out parameter results if we
/// successfully match.
static SelectPatternFlavor
MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
  SelectInst *SI = dyn_cast<SelectInst>(V);
  if (SI == 0) return SPF_UNKNOWN;

  ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
  if (ICI == 0) return SPF_UNKNOWN;

  LHS = ICI->getOperand(0);
  RHS = ICI->getOperand(1);

  // (icmp X, Y) ? X : Y
  if (SI->getTrueValue() == ICI->getOperand(0) &&
      SI->getFalseValue() == ICI->getOperand(1)) {
    switch (ICI->getPredicate()) {
    default: return SPF_UNKNOWN; // Equality.
    case ICmpInst::ICMP_UGT:
    case ICmpInst::ICMP_UGE: return SPF_UMAX;
    case ICmpInst::ICMP_SGT:
    case ICmpInst::ICMP_SGE: return SPF_SMAX;
    case ICmpInst::ICMP_ULT:
    case ICmpInst::ICMP_ULE: return SPF_UMIN;
    case ICmpInst::ICMP_SLT:
    case ICmpInst::ICMP_SLE: return SPF_SMIN;
    }
  }

  // (icmp X, Y) ? Y : X
  if (SI->getTrueValue() == ICI->getOperand(1) &&
      SI->getFalseValue() == ICI->getOperand(0)) {
    switch (ICI->getPredicate()) {
      default: return SPF_UNKNOWN; // Equality.
      case ICmpInst::ICMP_UGT:
      case ICmpInst::ICMP_UGE: return SPF_UMIN;
      case ICmpInst::ICMP_SGT:
      case ICmpInst::ICMP_SGE: return SPF_SMIN;
      case ICmpInst::ICMP_ULT:
      case ICmpInst::ICMP_ULE: return SPF_UMAX;
      case ICmpInst::ICMP_SLT:
      case ICmpInst::ICMP_SLE: return SPF_SMAX;
    }
  }

  // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)

  return SPF_UNKNOWN;
}


/// GetSelectFoldableOperands - We want to turn code that looks like this:
///   %C = or %A, %B
///   %D = select %cond, %C, %A
/// into:
///   %C = select %cond, %B, 0
///   %D = or %A, %C
///
/// Assuming that the specified instruction is an operand to the select, return
/// a bitmask indicating which operands of this instruction are foldable if they
/// equal the other incoming value of the select.
///
static unsigned GetSelectFoldableOperands(Instruction *I) {
  switch (I->getOpcode()) {
  case Instruction::Add:
  case Instruction::Mul:
  case Instruction::And:
  case Instruction::Or:
  case Instruction::Xor:
    return 3;              // Can fold through either operand.
  case Instruction::Sub:   // Can only fold on the amount subtracted.
  case Instruction::Shl:   // Can only fold on the shift amount.
  case Instruction::LShr:
  case Instruction::AShr:
    return 1;
  default:
    return 0;              // Cannot fold
  }
}

/// GetSelectFoldableConstant - For the same transformation as the previous
/// function, return the identity constant that goes into the select.
static Constant *GetSelectFoldableConstant(Instruction *I) {
  switch (I->getOpcode()) {
  default: llvm_unreachable("This cannot happen!");
  case Instruction::Add:
  case Instruction::Sub:
  case Instruction::Or:
  case Instruction::Xor:
  case Instruction::Shl:
  case Instruction::LShr:
  case Instruction::AShr:
    return Constant::getNullValue(I->getType());
  case Instruction::And:
    return Constant::getAllOnesValue(I->getType());
  case Instruction::Mul:
    return ConstantInt::get(I->getType(), 1);
  }
}

/// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
/// have the same opcode and only one use each.  Try to simplify this.
Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
                                          Instruction *FI) {
  if (TI->getNumOperands() == 1) {
    // If this is a non-volatile load or a cast from the same type,
    // merge.
    if (TI->isCast()) {
      if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
        return 0;
      // The select condition may be a vector. We may only change the operand
      // type if the vector width remains the same (and matches the condition).
      Type *CondTy = SI.getCondition