lib/CodeGen/PatchableFunction.cpp

   1 //===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements edits function bodies in place to support the
  11 // "patchable-function" attribute.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/CodeGen/MachineFunction.h"
  16 #include "llvm/CodeGen/MachineFunctionPass.h"
  17 #include "llvm/CodeGen/MachineInstrBuilder.h"
  18 #include "llvm/CodeGen/Passes.h"
  19 #include "llvm/CodeGen/TargetFrameLowering.h"
  20 #include "llvm/CodeGen/TargetInstrInfo.h"
  21 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  22
  23 using namespace llvm;
  24
  25 namespace {
  26 struct PatchableFunction : public MachineFunctionPass {
  27   static char ID; // Pass identification, replacement for typeid
  28   PatchableFunction() : MachineFunctionPass(ID) {
  29     initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
  30   }
  31
  32   bool runOnMachineFunction(MachineFunction &F) override;
  33    MachineFunctionProperties getRequiredProperties() const override {
  34     return MachineFunctionProperties().set(
  35         MachineFunctionProperties::Property::NoVRegs);
  36   }
  37 };
  38 }
  39
  40 /// Returns true if instruction \p MI will not result in actual machine code
  41 /// instructions.
  42 static bool doesNotGeneratecode(const MachineInstr &MI) {
  43   // TODO: Introduce an MCInstrDesc flag for this
  44   switch (MI.getOpcode()) {
  45   default: return false;
  46   case TargetOpcode::IMPLICIT_DEF:
  47   case TargetOpcode::KILL:
  48   case TargetOpcode::CFI_INSTRUCTION:
  49   case TargetOpcode::EH_LABEL:
  50   case TargetOpcode::GC_LABEL:
  51   case TargetOpcode::DBG_VALUE:
  52   case TargetOpcode::DBG_LABEL:
  53     return true;
  54   }
  55 }
  56
  57 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
  58   if (!MF.getFunction().hasFnAttribute("patchable-function"))
  59     return false;
  60
  61 #ifndef NDEBUG
  62   Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
  63   StringRef PatchType = PatchAttr.getValueAsString();
  64   assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
  65 #endif
  66
  67   auto &FirstMBB = *MF.begin();
  68   MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
  69   for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
  70     assert(FirstActualI != FirstMBB.end());
  71
  72   auto *TII = MF.getSubtarget().getInstrInfo();
  73   auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
  74                      TII->get(TargetOpcode::PATCHABLE_OP))
  75                  .addImm(2)
  76                  .addImm(FirstActualI->getOpcode());
  77
  78   for (auto &MO : FirstActualI->operands())
  79     MIB.add(MO);
  80
  81   FirstActualI->eraseFromParent();
  82   MF.ensureAlignment(4);
  83   return true;
  84 }
  85
  86 char PatchableFunction::ID = 0;
  87 char &llvm::PatchableFunctionID = PatchableFunction::ID;
  88 INITIALIZE_PASS(PatchableFunction, "patchable-function",
  89                 "Implement the 'patchable-function' attribute", false, false)