dfe05b84b3
As part of https://github.com/llvm/llvm-project/pull/174746 I encountered a compile time regression due to ResetMachineFunction performing full resets on empty functions. In normal operation, this behaviour is not likely to impact compile time, as the pass is only inserted when using GlobalISel. https://github.com/llvm/llvm-project/pull/174746 includes GlobalISel passes in the SDAG pipeline (only on AArch64) and skips them if a given function is not optnone surfacing this. By checking if the MachineFunction is empty we can perform a more lightweight reset that just sets the required flags, reducing the impact of this change.
107 lines
4.0 KiB
C++
107 lines
4.0 KiB
C++
//===-- ResetMachineFunctionPass.cpp - Reset Machine Function ----*- C++ -*-==//
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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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/// \file
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/// This file implements a pass that will conditionally reset a machine
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/// function as if it was just created. This is used to provide a fallback
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/// mechanism when GlobalISel fails, thus the condition for the reset to
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/// happen is that the MachineFunction has the FailedISel property.
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/ScopeExit.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/StackProtector.h"
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#include "llvm/IR/DiagnosticInfo.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Target/TargetMachine.h"
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using namespace llvm;
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#define DEBUG_TYPE "reset-machine-function"
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STATISTIC(NumFunctionsReset, "Number of functions reset");
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STATISTIC(NumFunctionsVisited, "Number of functions visited");
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namespace {
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class ResetMachineFunction : public MachineFunctionPass {
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/// Tells whether or not this pass should emit a fallback
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/// diagnostic when it resets a function.
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bool EmitFallbackDiag;
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/// Whether we should abort immediately instead of resetting the function.
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bool AbortOnFailedISel;
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public:
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static char ID; // Pass identification, replacement for typeid
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ResetMachineFunction(bool EmitFallbackDiag = false,
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bool AbortOnFailedISel = false)
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: MachineFunctionPass(ID), EmitFallbackDiag(EmitFallbackDiag),
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AbortOnFailedISel(AbortOnFailedISel) {}
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StringRef getPassName() const override { return "ResetMachineFunction"; }
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addPreserved<StackProtector>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool runOnMachineFunction(MachineFunction &MF) override {
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++NumFunctionsVisited;
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// No matter what happened, whether we successfully selected the function
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// or not, nothing is going to use the vreg types after us. Make sure they
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// disappear.
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llvm::scope_exit ClearVRegTypesOnReturn(
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[&MF]() { MF.getRegInfo().clearVirtRegTypes(); });
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if (!MF.getProperties().hasFailedISel())
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return false;
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if (AbortOnFailedISel)
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report_fatal_error("Instruction selection failed");
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LLVM_DEBUG(dbgs() << "Resetting: " << MF.getName() << '\n');
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++NumFunctionsReset;
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if (MF.empty()) {
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// Nothing was materialized in the MachineFunction, so avoid the cost of
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// tearing down and rebuilding all of the per-function state. Just clear
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// the FailedISel bit so the SelectionDAG pipeline can proceed.
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auto &Props = MF.getProperties();
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Props.resetToInitial();
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} else {
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MF.reset();
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MF.initTargetMachineFunctionInfo(MF.getSubtarget());
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const TargetMachine &TM = MF.getTarget();
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// MRI callback for target specific initializations.
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TM.registerMachineRegisterInfoCallback(MF);
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}
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if (EmitFallbackDiag) {
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const Function &F = MF.getFunction();
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DiagnosticInfoISelFallback DiagFallback(F);
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F.getContext().diagnose(DiagFallback);
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}
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return true;
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}
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};
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} // end anonymous namespace
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char ResetMachineFunction::ID = 0;
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INITIALIZE_PASS(ResetMachineFunction, DEBUG_TYPE,
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"Reset machine function if ISel failed", false, false)
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MachineFunctionPass *
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llvm::createResetMachineFunctionPass(bool EmitFallbackDiag = false,
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bool AbortOnFailedISel = false) {
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return new ResetMachineFunction(EmitFallbackDiag, AbortOnFailedISel);
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}
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