109 lines
3.5 KiB
C++
109 lines
3.5 KiB
C++
//===- NVPTXProxyRegErasure.cpp - NVPTX Proxy Register Instruction Erasure -==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// The pass is needed to remove ProxyReg instructions and restore related
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// registers. The instructions were needed at instruction selection stage to
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// make sure that callseq_end nodes won't be removed as "dead nodes". This can
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// happen when we expand instructions into libcalls and the call site doesn't
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// care about the libcall chain. Call site cares about data flow only, and the
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// latest data flow node happens to be before callseq_end. Therefore the node
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// becomes dangling and "dead". The ProxyReg acts like an additional data flow
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// node *after* the callseq_end in the chain and ensures that everything will be
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// preserved.
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//
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//===----------------------------------------------------------------------===//
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#include "NVPTX.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/TargetRegisterInfo.h"
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using namespace llvm;
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namespace {
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struct NVPTXProxyRegErasure : public MachineFunctionPass {
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static char ID;
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NVPTXProxyRegErasure() : MachineFunctionPass(ID) {}
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bool runOnMachineFunction(MachineFunction &MF) override;
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StringRef getPassName() const override {
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return "NVPTX Proxy Register Instruction Erasure";
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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};
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} // namespace
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char NVPTXProxyRegErasure::ID = 0;
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INITIALIZE_PASS(NVPTXProxyRegErasure, "nvptx-proxyreg-erasure",
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"NVPTX ProxyReg Erasure", false, false)
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bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
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SmallVector<MachineInstr *, 16> RemoveList;
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// ProxyReg instructions forward a register as another: `%dst = mov.iN %src`.
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// Bulk RAUW the `%dst` registers in two passes over the machine function.
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DenseMap<Register, Register> RAUWBatch;
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for (auto &BB : MF) {
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for (auto &MI : BB) {
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switch (MI.getOpcode()) {
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case NVPTX::ProxyRegB1:
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case NVPTX::ProxyRegB16:
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case NVPTX::ProxyRegB32:
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case NVPTX::ProxyRegB64: {
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auto &InOp = *MI.uses().begin();
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auto &OutOp = *MI.defs().begin();
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assert(InOp.isReg() && "ProxyReg input should be a register.");
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assert(OutOp.isReg() && "ProxyReg output should be a register.");
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RemoveList.push_back(&MI);
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Register replacement = InOp.getReg();
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// Check if the replacement itself has been replaced.
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if (auto it = RAUWBatch.find(replacement); it != RAUWBatch.end())
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replacement = it->second;
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RAUWBatch.try_emplace(OutOp.getReg(), replacement);
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break;
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}
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}
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}
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}
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// If there were no proxy instructions, exit early.
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if (RemoveList.empty())
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return false;
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// Erase the proxy instructions first.
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for (auto *MI : RemoveList) {
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MI->eraseFromParent();
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}
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// Now go replace the registers.
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for (auto &BB : MF) {
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for (auto &MI : BB) {
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for (auto &Op : MI.uses()) {
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if (!Op.isReg())
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continue;
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auto it = RAUWBatch.find(Op.getReg());
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if (it != RAUWBatch.end())
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Op.setReg(it->second);
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}
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}
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}
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return true;
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}
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MachineFunctionPass *llvm::createNVPTXProxyRegErasurePass() {
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return new NVPTXProxyRegErasure();
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}
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