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 #include "llvm/CodeGen/MachineFunctionPass.h"
20 using namespace llvm;
21 
22 #define DEBUG_TYPE "wasm-nullify-dbg-value-lists"
23 
24 namespace {
25 class WebAssemblyNullifyDebugValueLists final : public MachineFunctionPass {
26   StringRef getPassName() const override {
27     return "WebAssembly Nullify DBG_VALUE_LISTs";
28   }
29 
30   bool runOnMachineFunction(MachineFunction &MF) override;
31 
32 public:
33   static char ID; // Pass identification, replacement for typeid
34   WebAssemblyNullifyDebugValueLists() : MachineFunctionPass(ID) {}
35 };
36 } // end anonymous namespace
37 
38 char WebAssemblyNullifyDebugValueLists::ID = 0;
39 INITIALIZE_PASS(WebAssemblyNullifyDebugValueLists, DEBUG_TYPE,
40                 "WebAssembly Nullify DBG_VALUE_LISTs", false, false)
41 
42 FunctionPass *llvm::createWebAssemblyNullifyDebugValueLists() {
43   return new WebAssemblyNullifyDebugValueLists();
44 }
45 
46 bool WebAssemblyNullifyDebugValueLists::runOnMachineFunction(
47     MachineFunction &MF) {
48   LLVM_DEBUG(dbgs() << "********** Nullify DBG_VALUE_LISTs **********\n"
49                        "********** Function: "
50                     << MF.getName() << '\n');
51   const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
52   SmallVector<MachineInstr *, 2> DbgValueLists;
53   for (auto &MBB : MF)
54     for (auto &MI : MBB)
55       if (MI.getOpcode() == TargetOpcode::DBG_VALUE_LIST)
56         DbgValueLists.push_back(&MI);
57 
58   // Our backend, including WebAssemblyDebugValueManager, currently cannot
59   // handle DBG_VALUE_LISTs correctly. So this converts DBG_VALUE_LISTs to
60   // "DBG_VALUE $noreg", which will appear as "optimized out".
61   for (auto *DVL : DbgValueLists) {
62     BuildMI(*DVL->getParent(), DVL, DVL->getDebugLoc(),
63             TII.get(TargetOpcode::DBG_VALUE), false, Register(),
64             DVL->getOperand(0).getMetadata(), DVL->getOperand(1).getMetadata());
65     DVL->eraseFromParent();
66   }
67 
68   return !DbgValueLists.empty();
69 }
70