llvm/lib/Target/NVPTX/NVPTXPeephole.cpp

   1 //===-- NVPTXPeephole.cpp - NVPTX Peephole Optimiztions -------------------===//
   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 // In NVPTX, NVPTXFrameLowering will emit following instruction at the beginning
  10 // of a MachineFunction.
  11 //
  12 //   mov %SPL, %depot
  13 //   cvta.local %SP, %SPL
  14 //
  15 // Because Frame Index is a generic address and alloca can only return generic
  16 // pointer, without this pass the instructions producing alloca'ed address will
  17 // be based on %SP. NVPTXLowerAlloca tends to help replace store and load on
  18 // this address with their .local versions, but this may introduce a lot of
  19 // cvta.to.local instructions. Performance can be improved if we avoid casting
  20 // address back and forth and directly calculate local address based on %SPL.
  21 // This peephole pass optimizes these cases, for example
  22 //
  23 // It will transform the following pattern
  24 //    %0 = LEA_ADDRi64 %VRFrame64, 4
  25 //    %1 = cvta_to_local_64 %0
  26 //
  27 // into
  28 //    %1 = LEA_ADDRi64 %VRFrameLocal64, 4
  29 //
  30 // %VRFrameLocal64 is the virtual register name of %SPL
  31 //
  32 //===----------------------------------------------------------------------===//
  33
  34 #include "NVPTX.h"
  35 #include "NVPTXRegisterInfo.h"
  36 #include "NVPTXSubtarget.h"
  37 #include "llvm/CodeGen/MachineFunctionPass.h"
  38 #include "llvm/CodeGen/MachineInstrBuilder.h"
  39 #include "llvm/CodeGen/MachineRegisterInfo.h"
  40 #include "llvm/CodeGen/TargetInstrInfo.h"
  41 #include "llvm/CodeGen/TargetRegisterInfo.h"
  42
  43 using namespace llvm;
  44
  45 #define DEBUG_TYPE "nvptx-peephole"
  46
  47 namespace llvm {
  48 void initializeNVPTXPeepholePass(PassRegistry &);
  49 }
  50
  51 namespace {
  52 struct NVPTXPeephole : public MachineFunctionPass {
  53  public:
  54   static char ID;
  55   NVPTXPeephole() : MachineFunctionPass(ID) {
  56     initializeNVPTXPeepholePass(*PassRegistry::getPassRegistry());
  57   }
  58
  59   bool runOnMachineFunction(MachineFunction &MF) override;
  60
  61   StringRef getPassName() const override {
  62     return "NVPTX optimize redundant cvta.to.local instruction";
  63   }
  64
  65   void getAnalysisUsage(AnalysisUsage &AU) const override {
  66     MachineFunctionPass::getAnalysisUsage(AU);
  67   }
  68 };
  69 }
  70
  71 char NVPTXPeephole::ID = 0;
  72
  73 INITIALIZE_PASS(NVPTXPeephole, "nvptx-peephole", "NVPTX Peephole", false, false)
  74
  75 static bool isCVTAToLocalCombinationCandidate(MachineInstr &Root) {
  76   auto &MBB = *Root.getParent();
  77   auto &MF = *MBB.getParent();
  78   // Check current instruction is cvta.to.local
  79   if (Root.getOpcode() != NVPTX::cvta_to_local_64 &&
  80       Root.getOpcode() != NVPTX::cvta_to_local)
  81     return false;
  82
  83   auto &Op = Root.getOperand(1);
  84   const auto &MRI = MF.getRegInfo();
  85   MachineInstr *GenericAddrDef = nullptr;
  86   if (Op.isReg() && Op.getReg().isVirtual()) {
  87     GenericAddrDef = MRI.getUniqueVRegDef(Op.getReg());
  88   }
  89
  90   // Check the register operand is uniquely defined by LEA_ADDRi instruction
  91   if (!GenericAddrDef || GenericAddrDef->getParent() != &MBB ||
  92       (GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi64 &&
  93        GenericAddrDef->getOpcode() != NVPTX::LEA_ADDRi)) {
  94     return false;
  95   }
  96
  97   const NVPTXRegisterInfo *NRI =
  98       MF.getSubtarget<NVPTXSubtarget>().getRegisterInfo();
  99
 100   // Check the LEA_ADDRi operand is Frame index
 101   auto &BaseAddrOp = GenericAddrDef->getOperand(1);
 102   if (BaseAddrOp.isReg() && BaseAddrOp.getReg() == NRI->getFrameRegister(MF)) {
 103     return true;
 104   }
 105
 106   return false;
 107 }
 108
 109 static void CombineCVTAToLocal(MachineInstr &Root) {
 110   auto &MBB = *Root.getParent();
 111   auto &MF = *MBB.getParent();
 112   const auto &MRI = MF.getRegInfo();
 113   const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
 114   auto &Prev = *MRI.getUniqueVRegDef(Root.getOperand(1).getReg());
 115
 116   const NVPTXRegisterInfo *NRI =
 117       MF.getSubtarget<NVPTXSubtarget>().getRegisterInfo();
 118
 119   MachineInstrBuilder MIB =
 120       BuildMI(MF, Root.getDebugLoc(), TII->get(Prev.getOpcode()),
 121               Root.getOperand(0).getReg())
 122           .addReg(NRI->getFrameLocalRegister(MF))
 123           .add(Prev.getOperand(2));
 124
 125   MBB.insert((MachineBasicBlock::iterator)&Root, MIB);
 126
 127   // Check if MRI has only one non dbg use, which is Root
 128   if (MRI.hasOneNonDBGUse(Prev.getOperand(0).getReg())) {
 129     Prev.eraseFromParent();
 130   }
 131   Root.eraseFromParent();
 132 }
 133
 134 bool NVPTXPeephole::runOnMachineFunction(MachineFunction &MF) {
 135   if (skipFunction(MF.getFunction()))
 136     return false;
 137
 138   bool Changed = false;
 139   // Loop over all of the basic blocks.
 140   for (auto &MBB : MF) {
 141     // Traverse the basic block.
 142     auto BlockIter = MBB.begin();
 143
 144     while (BlockIter != MBB.end()) {
 145       auto &MI = *BlockIter++;
 146       if (isCVTAToLocalCombinationCandidate(MI)) {
 147         CombineCVTAToLocal(MI);
 148         Changed = true;
 149       }
 150     }  // Instruction
 151   }    // Basic Block
 152
 153   const NVPTXRegisterInfo *NRI =
 154       MF.getSubtarget<NVPTXSubtarget>().getRegisterInfo();
 155
 156   // Remove unnecessary %VRFrame = cvta.local %VRFrameLocal
 157   const auto &MRI = MF.getRegInfo();
 158   if (MRI.use_empty(NRI->getFrameRegister(MF))) {
 159     if (auto MI = MRI.getUniqueVRegDef(NRI->getFrameRegister(MF))) {
 160       MI->eraseFromParent();
 161     }
 162   }
 163
 164   return Changed;
 165 }
 166
 167 MachineFunctionPass *llvm::createNVPTXPeephole() { return new NVPTXPeephole(); }