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CmpInstAnalysis.h
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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).
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
Constant * getPredForICmpCode(unsigned Code, bool Sign, Type *OpTy, CmpInst::Predicate &Pred)
This is the complement of getICmpCode.
Type
MessagePack types as defined in the standard, with the exception of Integer being divided into a sign...
Definition: MsgPackReader.h:48
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
This class represents lattice values for constants.
Definition: AllocatorList.h:23
bool decomposeBitTestICmp(Value *LHS, Value *RHS, CmpInst::Predicate &Pred, Value *&X, APInt &Mask, bool LookThroughTrunc=true)
Decompose an icmp into the form ((X & Mask) pred 0) if possible.
unsigned getICmpCode(const ICmpInst *ICI, bool InvertPred=false)
Encode a icmp predicate into a three bit mask.
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:732
std::underlying_type< E >::type Mask()
Get a bitmask with 1s in all places up to the high-order bit of E&#39;s largest value.
Definition: BitmaskEnum.h:80
bool predicatesFoldable(CmpInst::Predicate P1, CmpInst::Predicate P2)
Return true if both predicates match sign or if at least one of them is an equality comparison (which...