include/llvm/Analysis/CmpInstAnalysis.h

   1 //===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file holds routines to help analyse compare instructions
  10 // and fold them into constants or other compare instructions
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_ANALYSIS_CMPINSTANALYSIS_H
  15 #define LLVM_ANALYSIS_CMPINSTANALYSIS_H
  16
  17 #include "llvm/IR/InstrTypes.h"
  18
  19 namespace llvm {
  20   class ICmpInst;
  21   class Value;
  22
  23   /// Encode a icmp predicate into a three bit mask. These bits are carefully
  24   /// arranged to allow folding of expressions such as:
  25   ///
  26   ///      (A < B) | (A > B) --> (A != B)
  27   ///
  28   /// Note that this is only valid if the first and second predicates have the
  29   /// same sign. It is illegal to do: (A u< B) | (A s> B)
  30   ///
  31   /// Three bits are used to represent the condition, as follows:
  32   ///   0  A > B
  33   ///   1  A == B
  34   ///   2  A < B
  35   ///
  36   /// <=>  Value  Definition
  37   /// 000     0   Always false
  38   /// 001     1   A >  B
  39   /// 010     2   A == B
  40   /// 011     3   A >= B
  41   /// 100     4   A <  B
  42   /// 101     5   A != B
  43   /// 110     6   A <= B
  44   /// 111     7   Always true
  45   ///
  46   unsigned getICmpCode(const ICmpInst *ICI, bool InvertPred = false);
  47
  48   /// This is the complement of getICmpCode. It turns a predicate code into
  49   /// either a constant true or false or the predicate for a new ICmp.
  50   /// The sign is passed in to determine which kind of predicate to use in the
  51   /// new ICmp instruction.
  52   /// Non-NULL return value will be a true or false constant.
  53   /// NULL return means a new ICmp is needed. The predicate is output in Pred.
  54   Constant *getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy,
  55                                CmpInst::Predicate &Pred);
  56
  57   /// Return true if both predicates match sign or if at least one of them is an
  58   /// equality comparison (which is signless).
  59   bool predicatesFoldable(CmpInst::Predicate P1, CmpInst::Predicate P2);
  60
  61   /// Decompose an icmp into the form ((X & Mask) pred 0) if possible. The
  62   /// returned predicate is either == or !=. Returns false if decomposition
  63   /// fails.
  64   bool decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate &Pred,
  65                             Value *&X, APInt &Mask,
  66                             bool LookThroughTrunc = true);
  67
  68 } // end namespace llvm
  69
  70 #endif