include/llvm/CodeGen/GlobalISel/GISelKnownBits.h

   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 //
   9 /// Provides analysis for querying information about KnownBits during GISel
  10 /// passes.
  11 //
  12 //===----------------------------------------------------------------------===//
  13 #ifndef LLVM_CODEGEN_GLOBALISEL_KNOWNBITSINFO_H
  14 #define LLVM_CODEGEN_GLOBALISEL_KNOWNBITSINFO_H
  15
  16 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
  17 #include "llvm/CodeGen/MachineFunctionPass.h"
  18 #include "llvm/CodeGen/Register.h"
  19 #include "llvm/IR/PassManager.h"
  20 #include "llvm/InitializePasses.h"
  21 #include "llvm/Pass.h"
  22 #include "llvm/Support/KnownBits.h"
  23
  24 namespace llvm {
  25
  26 class TargetLowering;
  27 class DataLayout;
  28
  29 class GISelKnownBits : public GISelChangeObserver {
  30   MachineFunction &MF;
  31   MachineRegisterInfo &MRI;
  32   const TargetLowering &TL;
  33   const DataLayout &DL;
  34
  35 public:
  36   GISelKnownBits(MachineFunction &MF);
  37   virtual ~GISelKnownBits() = default;
  38   void setMF(MachineFunction &MF);
  39   virtual void computeKnownBitsImpl(Register R, KnownBits &Known,
  40                                     const APInt &DemandedElts,
  41                                     unsigned Depth = 0);
  42
  43   // KnownBitsAPI
  44   KnownBits getKnownBits(Register R);
  45   // Calls getKnownBits for first operand def of MI.
  46   KnownBits getKnownBits(MachineInstr &MI);
  47   APInt getKnownZeroes(Register R);
  48   APInt getKnownOnes(Register R);
  49
  50   /// \return true if 'V & Mask' is known to be zero in DemandedElts. We use
  51   /// this predicate to simplify operations downstream.
  52   /// Mask is known to be zero for bits that V cannot have.
  53   bool maskedValueIsZero(Register Val, const APInt &Mask) {
  54     return Mask.isSubsetOf(getKnownBits(Val).Zero);
  55   }
  56
  57   /// \return true if the sign bit of Op is known to be zero.  We use this
  58   /// predicate to simplify operations downstream.
  59   bool signBitIsZero(Register Op);
  60
  61   // FIXME: Is this the right place for G_FRAME_INDEX? Should it be in
  62   // TargetLowering?
  63   void computeKnownBitsForFrameIndex(Register R, KnownBits &Known,
  64                                      const APInt &DemandedElts,
  65                                      unsigned Depth = 0);
  66   static unsigned inferAlignmentForFrameIdx(int FrameIdx, int Offset,
  67                                             const MachineFunction &MF);
  68   static void computeKnownBitsForAlignment(KnownBits &Known, unsigned Align);
  69
  70   // Try to infer alignment for MI.
  71   static unsigned inferPtrAlignment(const MachineInstr &MI);
  72
  73   // Observer API. No-op for non-caching implementation.
  74   void erasingInstr(MachineInstr &MI) override{};
  75   void createdInstr(MachineInstr &MI) override{};
  76   void changingInstr(MachineInstr &MI) override{};
  77   void changedInstr(MachineInstr &MI) override{};
  78
  79 protected:
  80   unsigned getMaxDepth() const { return 6; }
  81 };
  82
  83 /// To use KnownBitsInfo analysis in a pass,
  84 /// KnownBitsInfo &Info = getAnalysis<GISelKnownBitsInfoAnalysis>().get(MF);
  85 /// Add to observer if the Info is caching.
  86 /// WrapperObserver.addObserver(Info);
  87
  88 /// Eventually add other features such as caching/ser/deserializing
  89 /// to MIR etc. Those implementations can derive from GISelKnownBits
  90 /// and override computeKnownBitsImpl.
  91 class GISelKnownBitsAnalysis : public MachineFunctionPass {
  92   std::unique_ptr<GISelKnownBits> Info;
  93
  94 public:
  95   static char ID;
  96   GISelKnownBitsAnalysis() : MachineFunctionPass(ID) {
  97     initializeGISelKnownBitsAnalysisPass(*PassRegistry::getPassRegistry());
  98   }
  99   GISelKnownBits &get(MachineFunction &MF) {
 100     if (!Info)
 101       Info = std::make_unique<GISelKnownBits>(MF);
 102     return *Info.get();
 103   }
 104   void getAnalysisUsage(AnalysisUsage &AU) const override;
 105   bool runOnMachineFunction(MachineFunction &MF) override;
 106   void releaseMemory() override { Info.reset(); }
 107 };
 108 } // namespace llvm
 109
 110 #endif // ifdef