lib/CodeGen/PatchableFunction.cpp

   1 //===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
   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 // This file implements edits function bodies in place to support the
  10 // "patchable-function" attribute.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/CodeGen/MachineFunction.h"
  15 #include "llvm/CodeGen/MachineFunctionPass.h"
  16 #include "llvm/CodeGen/MachineInstrBuilder.h"
  17 #include "llvm/CodeGen/Passes.h"
  18 #include "llvm/CodeGen/TargetFrameLowering.h"
  19 #include "llvm/CodeGen/TargetInstrInfo.h"
  20 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  21
  22 using namespace llvm;
  23
  24 namespace {
  25 struct PatchableFunction : public MachineFunctionPass {
  26   static char ID; // Pass identification, replacement for typeid
  27   PatchableFunction() : MachineFunctionPass(ID) {
  28     initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
  29   }
  30
  31   bool runOnMachineFunction(MachineFunction &F) override;
  32    MachineFunctionProperties getRequiredProperties() const override {
  33     return MachineFunctionProperties().set(
  34         MachineFunctionProperties::Property::NoVRegs);
  35   }
  36 };
  37 }
  38
  39 /// Returns true if instruction \p MI will not result in actual machine code
  40 /// instructions.
  41 static bool doesNotGeneratecode(const MachineInstr &MI) {
  42   // TODO: Introduce an MCInstrDesc flag for this
  43   switch (MI.getOpcode()) {
  44   default: return false;
  45   case TargetOpcode::IMPLICIT_DEF:
  46   case TargetOpcode::KILL:
  47   case TargetOpcode::CFI_INSTRUCTION:
  48   case TargetOpcode::EH_LABEL:
  49   case TargetOpcode::GC_LABEL:
  50   case TargetOpcode::DBG_VALUE:
  51   case TargetOpcode::DBG_LABEL:
  52     return true;
  53   }
  54 }
  55
  56 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
  57   if (!MF.getFunction().hasFnAttribute("patchable-function"))
  58     return false;
  59
  60 #ifndef NDEBUG
  61   Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
  62   StringRef PatchType = PatchAttr.getValueAsString();
  63   assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
  64 #endif
  65
  66   auto &FirstMBB = *MF.begin();
  67   MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
  68   for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
  69     assert(FirstActualI != FirstMBB.end());
  70
  71   auto *TII = MF.getSubtarget().getInstrInfo();
  72   auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
  73                      TII->get(TargetOpcode::PATCHABLE_OP))
  74                  .addImm(2)
  75                  .addImm(FirstActualI->getOpcode());
  76
  77   for (auto &MO : FirstActualI->operands())
  78     MIB.add(MO);
  79
  80   FirstActualI->eraseFromParent();
  81   MF.ensureAlignment(Align(16));
  82   return true;
  83 }
  84
  85 char PatchableFunction::ID = 0;
  86 char &llvm::PatchableFunctionID = PatchableFunction::ID;
  87 INITIALIZE_PASS(PatchableFunction, "patchable-function",
  88                 "Implement the 'patchable-function' attribute", false, false)