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      1 //== llvm/CodeGen/GlobalISel/Localizer.h - Localizer -------------*- 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 /// \file This file describes the interface of the Localizer pass.
     11 /// This pass moves/duplicates constant-like instructions close to their uses.
     12 /// Its primarily goal is to workaround the deficiencies of the fast register
     13 /// allocator.
     14 /// With GlobalISel constants are all materialized in the entry block of
     15 /// a function. However, the fast allocator cannot rematerialize constants and
     16 /// has a lot more live-ranges to deal with and will most likely end up
     17 /// spilling a lot.
     18 /// By pushing the constants close to their use, we only create small
     19 /// live-ranges.
     20 //===----------------------------------------------------------------------===//
     21 
     22 #ifndef LLVM_CODEGEN_GLOBALISEL_LOCALIZER_H
     23 #define LLVM_CODEGEN_GLOBALISEL_LOCALIZER_H
     24 
     25 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
     26 #include "llvm/CodeGen/MachineFunctionPass.h"
     27 
     28 namespace llvm {
     29 // Forward declarations.
     30 class MachineRegisterInfo;
     31 
     32 /// This pass implements the localization mechanism described at the
     33 /// top of this file. One specificity of the implementation is that
     34 /// it will materialize one and only one instance of a constant per
     35 /// basic block, thus enabling reuse of that constant within that block.
     36 /// Moreover, it only materializes constants in blocks where they
     37 /// are used. PHI uses are considered happening at the end of the
     38 /// related predecessor.
     39 class Localizer : public MachineFunctionPass {
     40 public:
     41   static char ID;
     42 
     43 private:
     44   /// MRI contains all the register class/bank information that this
     45   /// pass uses and updates.
     46   MachineRegisterInfo *MRI;
     47 
     48   /// Check whether or not \p MI needs to be moved close to its uses.
     49   static bool shouldLocalize(const MachineInstr &MI);
     50 
     51   /// Check if \p MOUse is used in the same basic block as \p Def.
     52   /// If the use is in the same block, we say it is local.
     53   /// When the use is not local, \p InsertMBB will contain the basic
     54   /// block when to insert \p Def to have a local use.
     55   static bool isLocalUse(MachineOperand &MOUse, const MachineInstr &Def,
     56                          MachineBasicBlock *&InsertMBB);
     57 
     58   /// Initialize the field members using \p MF.
     59   void init(MachineFunction &MF);
     60 
     61 public:
     62   Localizer();
     63 
     64   StringRef getPassName() const override { return "Localizer"; }
     65 
     66   MachineFunctionProperties getRequiredProperties() const override {
     67     return MachineFunctionProperties()
     68         .set(MachineFunctionProperties::Property::IsSSA)
     69         .set(MachineFunctionProperties::Property::Legalized)
     70         .set(MachineFunctionProperties::Property::RegBankSelected);
     71   }
     72 
     73   bool runOnMachineFunction(MachineFunction &MF) override;
     74 };
     75 
     76 } // End namespace llvm.
     77 
     78 #endif
     79