llvm/llvm/include/llvm/Analysis/CmpInstAnalysis.h

//===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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/ADT/APInt.h"
#include "llvm/IR/InstrTypes.h"

namespace llvm {
  class Type;
  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(CmpInst::Predicate Pred);

  /// 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);

  /// Similar to getICmpCode but for FCmpInst. This encodes a fcmp predicate
  /// into a four bit mask.
  inline unsigned getFCmpCode(CmpInst::Predicate CC) { … }

  /// This is the complement of getFCmpCode. It turns a predicate code into
  /// either a constant true or false or the predicate for a new FCmp.
  /// 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 *getPredForFCmpCode(unsigned Code, Type *OpTy,
                               CmpInst::Predicate &Pred);

  /// Represents the operation icmp (X & Mask) pred 0, where pred can only be
  /// eq or ne.
  struct DecomposedBitTest { … };

  /// Decompose an icmp into the form ((X & Mask) pred 0) if possible.
  std::optional<DecomposedBitTest>
  decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate Pred,
                       bool LookThroughTrunc = true);

} // end namespace llvm

#endif