1 //=== WebAssemblyNullifyDebugValueLists.cpp - Nullify DBG_VALUE_LISTs   ---===//
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 /// \file
10 /// Nullify DBG_VALUE_LISTs instructions as a temporary measure before we
11 /// implement DBG_VALUE_LIST handling in WebAssemblyDebugValueManager.
12 /// See https://bugs.llvm.org/show_bug.cgi?id=50361.
13 /// TODO Correctly handle DBG_VALUE_LISTs
14 ///
15 //===----------------------------------------------------------------------===//
16 
17 #include "WebAssembly.h"
18 #include "WebAssemblySubtarget.h"
19 using namespace llvm;
20 
21 #define DEBUG_TYPE "wasm-nullify-dbg-value-lists"
22 
23 namespace {
24 class WebAssemblyNullifyDebugValueLists final : public MachineFunctionPass {
25   StringRef getPassName() const override {
26     return "WebAssembly Nullify DBG_VALUE_LISTs";
27   }
28 
29   bool runOnMachineFunction(MachineFunction &MF) override;
30 
31 public:
32   static char ID; // Pass identification, replacement for typeid
33   WebAssemblyNullifyDebugValueLists() : MachineFunctionPass(ID) {}
34 };
35 } // end anonymous namespace
36 
37 char WebAssemblyNullifyDebugValueLists::ID = 0;
38 INITIALIZE_PASS(WebAssemblyNullifyDebugValueLists, DEBUG_TYPE,
39                 "WebAssembly Nullify DBG_VALUE_LISTs", false, false)
40 
41 FunctionPass *llvm::createWebAssemblyNullifyDebugValueLists() {
42   return new WebAssemblyNullifyDebugValueLists();
43 }
44 
45 bool WebAssemblyNullifyDebugValueLists::runOnMachineFunction(
46     MachineFunction &MF) {
47   LLVM_DEBUG(dbgs() << "********** Nullify DBG_VALUE_LISTs **********\n"
48                        "********** Function: "
49                     << MF.getName() << '\n');
50   const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
51   SmallVector<MachineInstr *, 2> DbgValueLists;
52   for (auto &MBB : MF)
53     for (auto &MI : MBB)
54       if (MI.getOpcode() == TargetOpcode::DBG_VALUE_LIST)
55         DbgValueLists.push_back(&MI);
56 
57   // Our backend, including WebAssemblyDebugValueManager, currently cannot
58   // handle DBG_VALUE_LISTs correctly. So this converts DBG_VALUE_LISTs to
59   // "DBG_VALUE $noreg", which will appear as "optimized out".
60   for (auto *DVL : DbgValueLists) {
61     BuildMI(*DVL->getParent(), DVL, DVL->getDebugLoc(),
62             TII.get(TargetOpcode::DBG_VALUE), false, Register(),
63             DVL->getOperand(0).getMetadata(), DVL->getOperand(1).getMetadata());
64     DVL->eraseFromParent();
65   }
66 
67   return !DbgValueLists.empty();
68 }
69