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      1 //===- NVPTXProxyRegErasure.cpp - NVPTX Proxy Register Instruction Erasure -==//
      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 // The pass is needed to remove ProxyReg instructions and restore related
     10 // registers. The instructions were needed at instruction selection stage to
     11 // make sure that callseq_end nodes won't be removed as "dead nodes". This can
     12 // happen when we expand instructions into libcalls and the call site doesn't
     13 // care about the libcall chain. Call site cares about data flow only, and the
     14 // latest data flow node happens to be before callseq_end. Therefore the node
     15 // becomes dangling and "dead". The ProxyReg acts like an additional data flow
     16 // node *after* the callseq_end in the chain and ensures that everything will be
     17 // preserved.
     18 //
     19 //===----------------------------------------------------------------------===//
     20 
     21 #include "NVPTX.h"
     22 #include "llvm/CodeGen/MachineFunctionPass.h"
     23 #include "llvm/CodeGen/MachineInstrBuilder.h"
     24 #include "llvm/CodeGen/MachineRegisterInfo.h"
     25 #include "llvm/CodeGen/TargetInstrInfo.h"
     26 #include "llvm/CodeGen/TargetRegisterInfo.h"
     27 
     28 using namespace llvm;
     29 
     30 namespace llvm {
     31 void initializeNVPTXProxyRegErasurePass(PassRegistry &);
     32 }
     33 
     34 namespace {
     35 
     36 struct NVPTXProxyRegErasure : public MachineFunctionPass {
     37 public:
     38   static char ID;
     39   NVPTXProxyRegErasure() : MachineFunctionPass(ID) {
     40     initializeNVPTXProxyRegErasurePass(*PassRegistry::getPassRegistry());
     41   }
     42 
     43   bool runOnMachineFunction(MachineFunction &MF) override;
     44 
     45   StringRef getPassName() const override {
     46     return "NVPTX Proxy Register Instruction Erasure";
     47   }
     48 
     49   void getAnalysisUsage(AnalysisUsage &AU) const override {
     50     MachineFunctionPass::getAnalysisUsage(AU);
     51   }
     52 
     53 private:
     54   void replaceMachineInstructionUsage(MachineFunction &MF, MachineInstr &MI);
     55 
     56   void replaceRegisterUsage(MachineInstr &Instr, MachineOperand &From,
     57                             MachineOperand &To);
     58 };
     59 
     60 } // namespace
     61 
     62 char NVPTXProxyRegErasure::ID = 0;
     63 
     64 INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure", "NVPTX ProxyReg Erasure", false, false)
     65 
     66 bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
     67   SmallVector<MachineInstr *, 16> RemoveList;
     68 
     69   for (auto &BB : MF) {
     70     for (auto &MI : BB) {
     71       switch (MI.getOpcode()) {
     72       case NVPTX::ProxyRegI1:
     73       case NVPTX::ProxyRegI16:
     74       case NVPTX::ProxyRegI32:
     75       case NVPTX::ProxyRegI64:
     76       case NVPTX::ProxyRegF16:
     77       case NVPTX::ProxyRegF16x2:
     78       case NVPTX::ProxyRegF32:
     79       case NVPTX::ProxyRegF64:
     80         replaceMachineInstructionUsage(MF, MI);
     81         RemoveList.push_back(&MI);
     82         break;
     83       }
     84     }
     85   }
     86 
     87   for (auto *MI : RemoveList) {
     88     MI->eraseFromParent();
     89   }
     90 
     91   return !RemoveList.empty();
     92 }
     93 
     94 void NVPTXProxyRegErasure::replaceMachineInstructionUsage(MachineFunction &MF,
     95                                                           MachineInstr &MI) {
     96   auto &InOp = *MI.uses().begin();
     97   auto &OutOp = *MI.defs().begin();
     98 
     99   assert(InOp.isReg() && "ProxyReg input operand should be a register.");
    100   assert(OutOp.isReg() && "ProxyReg output operand should be a register.");
    101 
    102   for (auto &BB : MF) {
    103     for (auto &I : BB) {
    104       replaceRegisterUsage(I, OutOp, InOp);
    105     }
    106   }
    107 }
    108 
    109 void NVPTXProxyRegErasure::replaceRegisterUsage(MachineInstr &Instr,
    110                                                 MachineOperand &From,
    111                                                 MachineOperand &To) {
    112   for (auto &Op : Instr.uses()) {
    113     if (Op.isReg() && Op.getReg() == From.getReg()) {
    114       Op.setReg(To.getReg());
    115     }
    116   }
    117 }
    118 
    119 MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {
    120   return new NVPTXProxyRegErasure();
    121 }
    122