109 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// The pass is needed to remove ProxyReg instructions and restore related10// registers. The instructions were needed at instruction selection stage to11// make sure that callseq_end nodes won't be removed as "dead nodes". This can12// happen when we expand instructions into libcalls and the call site doesn't13// care about the libcall chain. Call site cares about data flow only, and the14// latest data flow node happens to be before callseq_end. Therefore the node15// becomes dangling and "dead". The ProxyReg acts like an additional data flow16// node *after* the callseq_end in the chain and ensures that everything will be17// preserved.18//19//===----------------------------------------------------------------------===//20 21#include "NVPTX.h"22#include "llvm/CodeGen/MachineFunctionPass.h"23#include "llvm/CodeGen/TargetRegisterInfo.h"24 25using namespace llvm;26 27namespace {28 29struct NVPTXProxyRegErasure : public MachineFunctionPass {30 static char ID;31 NVPTXProxyRegErasure() : MachineFunctionPass(ID) {}32 33 bool runOnMachineFunction(MachineFunction &MF) override;34 35 StringRef getPassName() const override {36 return "NVPTX Proxy Register Instruction Erasure";37 }38 39 void getAnalysisUsage(AnalysisUsage &AU) const override {40 MachineFunctionPass::getAnalysisUsage(AU);41 }42};43 44} // namespace45 46char NVPTXProxyRegErasure::ID = 0;47 48INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure",49 "NVPTX ProxyReg Erasure", false, false)50 51bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {52 SmallVector<MachineInstr *, 16> RemoveList;53 54 // ProxyReg instructions forward a register as another: `%dst = mov.iN %src`.55 // Bulk RAUW the `%dst` registers in two passes over the machine function.56 DenseMap<Register, Register> RAUWBatch;57 58 for (auto &BB : MF) {59 for (auto &MI : BB) {60 switch (MI.getOpcode()) {61 case NVPTX::ProxyRegB1:62 case NVPTX::ProxyRegB16:63 case NVPTX::ProxyRegB32:64 case NVPTX::ProxyRegB64: {65 auto &InOp = *MI.uses().begin();66 auto &OutOp = *MI.defs().begin();67 assert(InOp.isReg() && "ProxyReg input should be a register.");68 assert(OutOp.isReg() && "ProxyReg output should be a register.");69 RemoveList.push_back(&MI);70 Register replacement = InOp.getReg();71 // Check if the replacement itself has been replaced.72 if (auto it = RAUWBatch.find(replacement); it != RAUWBatch.end())73 replacement = it->second;74 RAUWBatch.try_emplace(OutOp.getReg(), replacement);75 break;76 }77 }78 }79 }80 81 // If there were no proxy instructions, exit early.82 if (RemoveList.empty())83 return false;84 85 // Erase the proxy instructions first.86 for (auto *MI : RemoveList) {87 MI->eraseFromParent();88 }89 90 // Now go replace the registers.91 for (auto &BB : MF) {92 for (auto &MI : BB) {93 for (auto &Op : MI.uses()) {94 if (!Op.isReg())95 continue;96 auto it = RAUWBatch.find(Op.getReg());97 if (it != RAUWBatch.end())98 Op.setReg(it->second);99 }100 }101 }102 103 return true;104}105 106MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {107 return new NVPTXProxyRegErasure();108}109