CmpInstAnalysis.h

Go to the documentation of this file.

//===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file holds routines to help analyse compare instructions
// and fold them into constants or other compare instructions
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ANALYSIS_CMPINSTANALYSIS_H
#define LLVM_ANALYSIS_CMPINSTANALYSIS_H

#include "llvm/IR/InstrTypes.h"

namespace llvm {
  class ICmpInst;
  class Value;

  /// Encode a icmp predicate into a three bit mask. These bits are carefully
  /// arranged to allow folding of expressions such as:
  ///
  ///      (A < B) | (A > B) --> (A != B)
  ///
  /// Note that this is only valid if the first and second predicates have the
  /// same sign. It is illegal to do: (A u< B) | (A s> B)
  ///
  /// Three bits are used to represent the condition, as follows:
  ///   0  A > B
  ///   1  A == B
  ///   2  A < B
  ///
  /// <=>  Value  Definition
  /// 000     0   Always false
  /// 001     1   A >  B
  /// 010     2   A == B
  /// 011     3   A >= B
  /// 100     4   A <  B
  /// 101     5   A != B
  /// 110     6   A <= B
  /// 111     7   Always true
  ///
  unsigned getICmpCode(const ICmpInst *ICI, bool InvertPred = false);

  /// This is the complement of getICmpCode. It turns a predicate code into
  /// either a constant true or false or the predicate for a new ICmp.
  /// The sign is passed in to determine which kind of predicate to use in the
  /// new ICmp instruction.
  /// Non-NULL return value will be a true or false constant.
  /// NULL return means a new ICmp is needed. The predicate is output in Pred.
  Constant *getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
                               CmpInst::Predicate &Pred);

  /// Return true if both predicates match sign or if at least one of them is an
  /// equality comparison (which is signless).
  bool predicatesFoldable(CmpInst::Predicate P1, CmpInst::Predicate P2);

  /// Decompose an icmp into the form ((X & Mask) pred 0) if possible. The
  /// returned predicate is either == or !=. Returns false if decomposition
  /// fails.
  bool decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate &Pred,
                            Value *&X, APInt &Mask,
                            bool LookThroughTrunc = true);

} // end namespace llvm

#endif