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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/Passes.h"
16 #include "llvm/CodeGen/MachineFunction.h"
17 #include "llvm/CodeGen/MachineFunctionPass.h"
18 #include "llvm/CodeGen/MachineInstrBuilder.h"
19 #include "llvm/Target/TargetFrameLowering.h"
20 #include "llvm/Target/TargetInstrInfo.h"
21 #include "llvm/Target/TargetSubtargetInfo.h"
22 
23 using namespace llvm;
24 
25 namespace {
26 struct PatchableFunction : public MachineFunctionPass {
27   static char ID; // Pass identification, replacement for typeid
PatchableFunction__anonc402d89f0111::PatchableFunction28   PatchableFunction() : MachineFunctionPass(ID) {
29     initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
30   }
31 
32   bool runOnMachineFunction(MachineFunction &F) override;
getRequiredProperties__anonc402d89f0111::PatchableFunction33    MachineFunctionProperties getRequiredProperties() const override {
34     return MachineFunctionProperties().set(
35         MachineFunctionProperties::Property::AllVRegsAllocated);
36   }
37 };
38 }
39 
40 /// Returns true if instruction \p MI will not result in actual machine code
41 /// instructions.
doesNotGeneratecode(const MachineInstr & MI)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     return true;
53   }
54 }
55 
runOnMachineFunction(MachineFunction & MF)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.addOperand(MO);
79 
80   FirstActualI->eraseFromParent();
81   MF.ensureAlignment(4);
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)
89