lib/CodeGen/MIRVRegNamerUtils.h

   1
   2 //===------------ MIRVRegNamerUtils.h - MIR VReg Renaming Utilities -------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // The purpose of these utilities is to abstract out parts of the MIRCanon pass
  11 // that are responsible for renaming virtual registers with the purpose of
  12 // sharing code with a MIRVRegNamer pass that could be the analog of the
  13 // opt -instnamer pass.
  14 //
  15 //===----------------------------------------------------------------------===//
  16
  17 #ifndef LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
  18 #define LLVM_LIB_CODEGEN_MIRVREGNAMERUTILS_H
  19
  20 #include "llvm/ADT/PostOrderIterator.h"
  21 #include "llvm/ADT/STLExtras.h"
  22 #include "llvm/CodeGen/MachineFunctionPass.h"
  23 #include "llvm/CodeGen/MachineInstrBuilder.h"
  24 #include "llvm/CodeGen/MachineRegisterInfo.h"
  25 #include "llvm/CodeGen/Passes.h"
  26 #include "llvm/Support/raw_ostream.h"
  27
  28 #include <queue>
  29
  30 namespace llvm {
  31
  32 /// NamedVRegCursor - The cursor is an object that keeps track of what the next
  33 /// vreg name should be. It does book keeping to determine when to skip the
  34 /// index value and by how much, or if the next vreg name should be an increment
  35 /// from the previous.
  36 class NamedVRegCursor {
  37   MachineRegisterInfo &MRI;
  38
  39   /// virtualVRegNumber - Book keeping of the last vreg position.
  40   unsigned virtualVRegNumber;
  41
  42   /// SkipGapSize - Used to calculate a modulo amount to skip by after every
  43   /// sequence of instructions starting from a given side-effecting
  44   /// MachineInstruction for a given MachineBasicBlock. The general idea is that
  45   /// for a given program compiled with two different opt pipelines, there
  46   /// shouldn't be greater than SkipGapSize difference in how many vregs are in
  47   /// play between the two and for every def-use graph of vregs we rename we
  48   /// will round up to the next SkipGapSize'th number so that we have a high
  49   /// change of landing on the same name for two given matching side-effects
  50   /// for the two compilation outcomes.
  51   const unsigned SkipGapSize;
  52
  53   /// RenamedInOtherBB - VRegs that we already renamed: ie breadcrumbs.
  54   std::vector<Register> RenamedInOtherBB;
  55
  56 public:
  57   NamedVRegCursor() = delete;
  58   /// 1000 for the SkipGapSize was a good heuristic at the time of the writing
  59   /// of the MIRCanonicalizerPass. Adjust as needed.
  60   NamedVRegCursor(MachineRegisterInfo &MRI, unsigned SkipGapSize = 1000)
  61       : MRI(MRI), virtualVRegNumber(0), SkipGapSize(SkipGapSize) {}
  62
  63   /// SkipGapSize - Skips modulo a gap value of indices. Indices are used to
  64   /// produce the next vreg name.
  65   void skipVRegs();
  66
  67   unsigned getVirtualVReg() const { return virtualVRegNumber; }
  68
  69   /// incrementVirtualVReg - This increments an index value that us used to
  70   /// create a new vreg name. This is not a Register.
  71   unsigned incrementVirtualVReg(unsigned incr = 1) {
  72     virtualVRegNumber += incr;
  73     return virtualVRegNumber;
  74   }
  75
  76   /// createVirtualRegister - Given an existing vreg, create a named vreg to
  77   /// take its place.
  78   unsigned createVirtualRegister(unsigned VReg);
  79
  80   /// renameVRegs - For a given MachineBasicBlock, scan for side-effecting
  81   /// instructions, walk the def-use from each side-effecting root (in sorted
  82   /// root order) and rename the encountered vregs in the def-use graph in a
  83   /// canonical ordering. This method maintains book keeping for which vregs
  84   /// were already renamed in RenamedInOtherBB.
  85   // @return changed
  86   bool renameVRegs(MachineBasicBlock *MBB);
  87 };
  88
  89 } // namespace llvm
  90
  91 #endif