1//===-- CmpInstAnalysis.h - Utils to help fold compare insts ----*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file holds routines to help analyse compare instructions
11// and fold them into constants or other compare instructions
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_TRANSFORMS_UTILS_CMPINSTANALYSIS_H
16#define LLVM_TRANSFORMS_UTILS_CMPINSTANALYSIS_H
17
18#include "llvm/IR/InstrTypes.h"
19
20namespace llvm {
21  class ICmpInst;
22  class Value;
23
24  /// Encode a icmp predicate into a three bit mask. These bits are carefully
25  /// arranged to allow folding of expressions such as:
26  ///
27  ///      (A < B) | (A > B) --> (A != B)
28  ///
29  /// Note that this is only valid if the first and second predicates have the
30  /// same sign. It is illegal to do: (A u< B) | (A s> B)
31  ///
32  /// Three bits are used to represent the condition, as follows:
33  ///   0  A > B
34  ///   1  A == B
35  ///   2  A < B
36  ///
37  /// <=>  Value  Definition
38  /// 000     0   Always false
39  /// 001     1   A >  B
40  /// 010     2   A == B
41  /// 011     3   A >= B
42  /// 100     4   A <  B
43  /// 101     5   A != B
44  /// 110     6   A <= B
45  /// 111     7   Always true
46  ///
47  unsigned getICmpCode(const ICmpInst *ICI, bool InvertPred = false);
48
49  /// This is the complement of getICmpCode, which turns an opcode and two
50  /// operands into either a constant true or false, or the predicate for a new
51  /// ICmp instruction. The sign is passed in to determine which kind of
52  /// predicate to use in the new icmp instruction.
53  /// Non-NULL return value will be a true or false constant.
54  /// NULL return means a new ICmp is needed. The predicate for which is output
55  /// in NewICmpPred.
56  Value *getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS,
57                      CmpInst::Predicate &NewICmpPred);
58
59  /// Return true if both predicates match sign or if at least one of them is an
60  /// equality comparison (which is signless).
61  bool PredicatesFoldable(CmpInst::Predicate p1, CmpInst::Predicate p2);
62
63  /// Decompose an icmp into the form ((X & Y) pred Z) if possible. The returned
64  /// predicate is either == or !=. Returns false if decomposition fails.
65  bool decomposeBitTestICmp(const ICmpInst *I, CmpInst::Predicate &Pred,
66                            Value *&X, Value *&Y, Value *&Z);
67
68} // end namespace llvm
69
70#endif
71