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//===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file holds routines to help analyse compare instructions
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// and fold them into constants or other compare instructions
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CMPINSTANALYSIS_H
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#define LLVM_ANALYSIS_CMPINSTANALYSIS_H
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#include "llvm/IR/InstrTypes.h"
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namespace llvm {
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  class Type;
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  class Value;
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  /// Encode a icmp predicate into a three bit mask. These bits are carefully
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  /// arranged to allow folding of expressions such as:
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  ///
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  ///      (A < B) | (A > B) --> (A != B)
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  ///
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  /// Note that this is only valid if the first and second predicates have the
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  /// same sign. It is illegal to do: (A u< B) | (A s> B)
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  ///
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  /// Three bits are used to represent the condition, as follows:
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  ///   0  A > B
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  ///   1  A == B
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  ///   2  A < B
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  ///
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  /// <=>  Value  Definition
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  /// 000     0   Always false
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  /// 001     1   A >  B
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  /// 010     2   A == B
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  /// 011     3   A >= B
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  /// 100     4   A <  B
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  /// 101     5   A != B
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  /// 110     6   A <= B
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  /// 111     7   Always true
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  ///
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  unsigned getICmpCode(CmpInst::Predicate Pred);
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  /// This is the complement of getICmpCode. It turns a predicate code into
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  /// either a constant true or false or the predicate for a new ICmp.
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  /// The sign is passed in to determine which kind of predicate to use in the
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  /// new ICmp instruction.
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  /// Non-NULL return value will be a true or false constant.
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  /// NULL return means a new ICmp is needed. The predicate is output in Pred.
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  Constant *getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
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                               CmpInst::Predicate &Pred);
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  /// Return true if both predicates match sign or if at least one of them is an
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  /// equality comparison (which is signless).
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  bool predicatesFoldable(CmpInst::Predicate P1, CmpInst::Predicate P2);
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  /// Similar to getICmpCode but for FCmpInst. This encodes a fcmp predicate
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  /// into a four bit mask.
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  inline unsigned getFCmpCode(CmpInst::Predicate CC) {
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    assert(CmpInst::FCMP_FALSE <= CC && CC <= CmpInst::FCMP_TRUE &&
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           "Unexpected FCmp predicate!");
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    // Take advantage of the bit pattern of CmpInst::Predicate here.
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    //                                          U L G E
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    static_assert(CmpInst::FCMP_FALSE == 0); // 0 0 0 0
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    static_assert(CmpInst::FCMP_OEQ == 1);   // 0 0 0 1
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    static_assert(CmpInst::FCMP_OGT == 2);   // 0 0 1 0
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    static_assert(CmpInst::FCMP_OGE == 3);   // 0 0 1 1
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    static_assert(CmpInst::FCMP_OLT == 4);   // 0 1 0 0
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    static_assert(CmpInst::FCMP_OLE == 5);   // 0 1 0 1
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    static_assert(CmpInst::FCMP_ONE == 6);   // 0 1 1 0
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    static_assert(CmpInst::FCMP_ORD == 7);   // 0 1 1 1
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    static_assert(CmpInst::FCMP_UNO == 8);   // 1 0 0 0
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    static_assert(CmpInst::FCMP_UEQ == 9);   // 1 0 0 1
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    static_assert(CmpInst::FCMP_UGT == 10);  // 1 0 1 0
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    static_assert(CmpInst::FCMP_UGE == 11);  // 1 0 1 1
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    static_assert(CmpInst::FCMP_ULT == 12);  // 1 1 0 0
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    static_assert(CmpInst::FCMP_ULE == 13);  // 1 1 0 1
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    static_assert(CmpInst::FCMP_UNE == 14);  // 1 1 1 0
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    static_assert(CmpInst::FCMP_TRUE == 15); // 1 1 1 1
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    return CC;
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  }
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  /// This is the complement of getFCmpCode. It turns a predicate code into
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  /// either a constant true or false or the predicate for a new FCmp.
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  /// Non-NULL return value will be a true or false constant.
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  /// NULL return means a new ICmp is needed. The predicate is output in Pred.
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  Constant *getPredForFCmpCode(unsigned Code, Type *OpTy,
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                               CmpInst::Predicate &Pred);
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  /// Decompose an icmp into the form ((X & Mask) pred 0) if possible. The
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  /// returned predicate is either == or !=. Returns false if decomposition
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  /// fails.
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  bool decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate &Pred,
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                            Value *&X, APInt &Mask,
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                            bool LookThroughTrunc = true);
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} // end namespace llvm
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#endif