1//===- llvm/CodeGen/GlobalISel/GISelKnownBits.h ---------------*- 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/// \file
9/// Provides analysis for querying information about KnownBits during GISel
10/// passes.
11///
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CODEGEN_GLOBALISEL_GISELKNOWNBITS_H
15#define LLVM_CODEGEN_GLOBALISEL_GISELKNOWNBITS_H
16
17#include "llvm/ADT/DenseMap.h"
18#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/CodeGen/Register.h"
21#include "llvm/InitializePasses.h"
22#include "llvm/Support/KnownBits.h"
23
24namespace llvm {
25
26class TargetLowering;
27class DataLayout;
28
29class GISelKnownBits : public GISelChangeObserver {
30 MachineFunction &MF;
31 MachineRegisterInfo &MRI;
32 const TargetLowering &TL;
33 const DataLayout &DL;
34 unsigned MaxDepth;
35 /// Cache maintained during a computeKnownBits request.
36 SmallDenseMap<Register, KnownBits, 16> ComputeKnownBitsCache;
37
38 void computeKnownBitsMin(Register Src0, Register Src1, KnownBits &Known,
39 const APInt &DemandedElts,
40 unsigned Depth = 0);
41
42 unsigned computeNumSignBitsMin(Register Src0, Register Src1,
43 const APInt &DemandedElts, unsigned Depth = 0);
44
45public:
46 GISelKnownBits(MachineFunction &MF, unsigned MaxDepth = 6);
47 virtual ~GISelKnownBits() = default;
48
49 const MachineFunction &getMachineFunction() const {
50 return MF;
51 }
52
53 const DataLayout &getDataLayout() const {
54 return DL;
55 }
56
57 virtual void computeKnownBitsImpl(Register R, KnownBits &Known,
58 const APInt &DemandedElts,
59 unsigned Depth = 0);
60
61 unsigned computeNumSignBits(Register R, const APInt &DemandedElts,
62 unsigned Depth = 0);
63 unsigned computeNumSignBits(Register R, unsigned Depth = 0);
64
65 // KnownBitsAPI
66 KnownBits getKnownBits(Register R);
67 KnownBits getKnownBits(Register R, const APInt &DemandedElts,
68 unsigned Depth = 0);
69
70 // Calls getKnownBits for first operand def of MI.
71 KnownBits getKnownBits(MachineInstr &MI);
72 APInt getKnownZeroes(Register R);
73 APInt getKnownOnes(Register R);
74
75 /// \return true if 'V & Mask' is known to be zero in DemandedElts. We use
76 /// this predicate to simplify operations downstream.
77 /// Mask is known to be zero for bits that V cannot have.
78 bool maskedValueIsZero(Register Val, const APInt &Mask) {
79 return Mask.isSubsetOf(RHS: getKnownBits(R: Val).Zero);
80 }
81
82 /// \return true if the sign bit of Op is known to be zero. We use this
83 /// predicate to simplify operations downstream.
84 bool signBitIsZero(Register Op);
85
86 static void computeKnownBitsForAlignment(KnownBits &Known,
87 Align Alignment) {
88 // The low bits are known zero if the pointer is aligned.
89 Known.Zero.setLowBits(Log2(A: Alignment));
90 }
91
92 /// \return The known alignment for the pointer-like value \p R.
93 Align computeKnownAlignment(Register R, unsigned Depth = 0);
94
95 // Observer API. No-op for non-caching implementation.
96 void erasingInstr(MachineInstr &MI) override {}
97 void createdInstr(MachineInstr &MI) override {}
98 void changingInstr(MachineInstr &MI) override {}
99 void changedInstr(MachineInstr &MI) override {}
100
101protected:
102 unsigned getMaxDepth() const { return MaxDepth; }
103};
104
105/// To use KnownBitsInfo analysis in a pass,
106/// KnownBitsInfo &Info = getAnalysis<GISelKnownBitsInfoAnalysis>().get(MF);
107/// Add to observer if the Info is caching.
108/// WrapperObserver.addObserver(Info);
109
110/// Eventually add other features such as caching/ser/deserializing
111/// to MIR etc. Those implementations can derive from GISelKnownBits
112/// and override computeKnownBitsImpl.
113class GISelKnownBitsAnalysis : public MachineFunctionPass {
114 std::unique_ptr<GISelKnownBits> Info;
115
116public:
117 static char ID;
118 GISelKnownBitsAnalysis() : MachineFunctionPass(ID) {
119 initializeGISelKnownBitsAnalysisPass(*PassRegistry::getPassRegistry());
120 }
121 GISelKnownBits &get(MachineFunction &MF);
122 void getAnalysisUsage(AnalysisUsage &AU) const override;
123 bool runOnMachineFunction(MachineFunction &MF) override;
124 void releaseMemory() override { Info.reset(); }
125};
126} // namespace llvm
127
128#endif // LLVM_CODEGEN_GLOBALISEL_GISELKNOWNBITS_H
129

source code of llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h