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89 lines
3.0 KiB
C++
89 lines
3.0 KiB
C++
//===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements edits function bodies in place to support the
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// "patchable-function" attribute.
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//
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//===----------------------------------------------------------------------===//
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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/MachineInstrBuilder.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/TargetFrameLowering.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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using namespace llvm;
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namespace {
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struct PatchableFunction : public MachineFunctionPass {
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static char ID; // Pass identification, replacement for typeid
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PatchableFunction() : MachineFunctionPass(ID) {
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initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &F) override;
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MachineFunctionProperties getRequiredProperties() const override {
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return MachineFunctionProperties().set(
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MachineFunctionProperties::Property::NoVRegs);
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}
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};
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}
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/// Returns true if instruction \p MI will not result in actual machine code
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/// instructions.
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static bool doesNotGeneratecode(const MachineInstr &MI) {
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// TODO: Introduce an MCInstrDesc flag for this
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switch (MI.getOpcode()) {
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default: return false;
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case TargetOpcode::IMPLICIT_DEF:
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case TargetOpcode::KILL:
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case TargetOpcode::CFI_INSTRUCTION:
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case TargetOpcode::EH_LABEL:
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case TargetOpcode::GC_LABEL:
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case TargetOpcode::DBG_VALUE:
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return true;
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}
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}
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bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
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if (!MF.getFunction().hasFnAttribute("patchable-function"))
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return false;
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#ifndef NDEBUG
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Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
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StringRef PatchType = PatchAttr.getValueAsString();
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assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
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#endif
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auto &FirstMBB = *MF.begin();
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MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
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for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
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assert(FirstActualI != FirstMBB.end());
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auto *TII = MF.getSubtarget().getInstrInfo();
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auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_OP))
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.addImm(2)
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.addImm(FirstActualI->getOpcode());
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for (auto &MO : FirstActualI->operands())
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MIB.add(MO);
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FirstActualI->eraseFromParent();
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MF.ensureAlignment(4);
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return true;
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}
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char PatchableFunction::ID = 0;
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char &llvm::PatchableFunctionID = PatchableFunction::ID;
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INITIALIZE_PASS(PatchableFunction, "patchable-function",
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"Implement the 'patchable-function' attribute", false, false)
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