llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp

   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 }