1 //===-- WebAssemblyDebugFixup.cpp - Debug Fixup ------------------===//
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 /// Several prior passes may "stackify" registers, here we ensure any references
11 /// in such registers in debug_value instructions become stack relative also.
12 /// This is done in a separate pass such that not all previous passes need to
13 /// track stack depth when values get stackified.
14 ///
15 //===----------------------------------------------------------------------===//
16 
17 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
18 #include "Utils/WebAssemblyUtilities.h"
19 #include "WebAssembly.h"
20 #include "WebAssemblyMachineFunctionInfo.h"
21 #include "WebAssemblySubtarget.h"
22 #include "llvm/ADT/SCCIterator.h"
23 #include "llvm/CodeGen/MachineFrameInfo.h"
24 #include "llvm/CodeGen/MachineFunction.h"
25 #include "llvm/CodeGen/MachineInstrBuilder.h"
26 #include "llvm/CodeGen/MachineLoopInfo.h"
27 #include "llvm/CodeGen/MachineRegisterInfo.h"
28 #include "llvm/CodeGen/Passes.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/raw_ostream.h"
31 using namespace llvm;
32 
33 #define DEBUG_TYPE "wasm-debug-fixup"
34 
35 namespace {
36 class WebAssemblyDebugFixup final : public MachineFunctionPass {
37   StringRef getPassName() const override { return "WebAssembly Debug Fixup"; }
38 
39   void getAnalysisUsage(AnalysisUsage &AU) const override {
40     AU.setPreservesCFG();
41     MachineFunctionPass::getAnalysisUsage(AU);
42   }
43 
44   bool runOnMachineFunction(MachineFunction &MF) override;
45 
46 public:
47   static char ID; // Pass identification, replacement for typeid
48   WebAssemblyDebugFixup() : MachineFunctionPass(ID) {}
49 };
50 } // end anonymous namespace
51 
52 char WebAssemblyDebugFixup::ID = 0;
53 INITIALIZE_PASS(
54     WebAssemblyDebugFixup, DEBUG_TYPE,
55     "Ensures debug_value's that have been stackified become stack relative",
56     false, false)
57 
58 FunctionPass *llvm::createWebAssemblyDebugFixup() {
59   return new WebAssemblyDebugFixup();
60 }
61 
62 bool WebAssemblyDebugFixup::runOnMachineFunction(MachineFunction &MF) {
63   LLVM_DEBUG(dbgs() << "********** Debug Fixup **********\n"
64                        "********** Function: "
65                     << MF.getName() << '\n');
66 
67   WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
68   const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
69 
70   struct StackElem {
71     unsigned Reg;
72     MachineInstr *DebugValue;
73   };
74   std::vector<StackElem> Stack;
75   for (MachineBasicBlock &MBB : MF) {
76     // We may insert into this list.
77     for (auto MII = MBB.begin(); MII != MBB.end(); ++MII) {
78       MachineInstr &MI = *MII;
79       if (MI.isDebugValue()) {
80         auto &MO = MI.getOperand(0);
81         // Also check if not a $noreg: likely a DBG_VALUE we just inserted.
82         if (MO.isReg() && MO.getReg().isValid() &&
83             MFI.isVRegStackified(MO.getReg())) {
84           // Found a DBG_VALUE with a stackified register we will
85           // change into a stack operand.
86           // Search for register rather than assume it is on top (which it
87           // typically is if it appears right after the def), since
88           // DBG_VALUE's may shift under some circumstances.
89           for (auto &Elem : reverse(Stack)) {
90             if (MO.getReg() == Elem.Reg) {
91               auto Depth = static_cast<unsigned>(&Elem - &Stack[0]);
92               LLVM_DEBUG(dbgs() << "Debug Value VReg " << MO.getReg()
93                                 << " -> Stack Relative " << Depth << "\n");
94               MO.ChangeToTargetIndex(WebAssembly::TI_OPERAND_STACK, Depth);
95               // Save the DBG_VALUE instruction that defined this stackified
96               // variable since later we need it to construct another one on
97               // pop.
98               Elem.DebugValue = &MI;
99               break;
100             }
101           }
102           // If the Reg was not found, we have a DBG_VALUE outside of its
103           // def-use range, and we leave it unmodified as reg, which means
104           // it will be culled later.
105         }
106       } else {
107         // Track stack depth.
108         for (MachineOperand &MO : reverse(MI.explicit_uses())) {
109           if (MO.isReg() && MFI.isVRegStackified(MO.getReg())) {
110             auto Prev = Stack.back();
111             Stack.pop_back();
112             assert(Prev.Reg == MO.getReg() &&
113                    "WebAssemblyDebugFixup: Pop: Register not matched!");
114             // We should not put a DBG_VALUE after a terminator; debug ranges
115             // are terminated at the end of a BB anyway.
116             if (Prev.DebugValue && !MI.isTerminator()) {
117               // This stackified reg is a variable that started life at
118               // Prev.DebugValue, so now that we're popping it we must insert
119               // a $noreg DBG_VALUE for the variable to end it, right after
120               // the current instruction.
121               BuildMI(*Prev.DebugValue->getParent(), std::next(MII),
122                       Prev.DebugValue->getDebugLoc(),
123                       TII->get(WebAssembly::DBG_VALUE), false, Register(),
124                       Prev.DebugValue->getOperand(2).getMetadata(),
125                       Prev.DebugValue->getOperand(3).getMetadata());
126             }
127           }
128         }
129         for (MachineOperand &MO : MI.defs()) {
130           if (MO.isReg() && MFI.isVRegStackified(MO.getReg())) {
131             Stack.push_back({MO.getReg(), nullptr});
132           }
133         }
134       }
135     }
136     assert(Stack.empty() &&
137            "WebAssemblyDebugFixup: Stack not empty at end of basic block!");
138   }
139 
140   return true;
141 }
142