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[codeview] Generalize DIExpression parsing to handle load chains
Summary: Hopefully this also clarifies exactly when and why we're rewriting certiain S_LOCALs using reference types: We're using the reference type to stand in for a zero-offset load. Reviewers: inglorion Subscribers: llvm-commits, hiraditya Differential Revision: https://reviews.llvm.org/D37309 llvm-svn: 312247
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@ -949,11 +949,19 @@ void CodeViewDebug::collectVariableInfoFromMFTable(
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}
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}
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static bool canUseReferenceType(const DbgVariableLocation &Loc) {
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return !Loc.LoadChain.empty() && Loc.LoadChain.back() == 0;
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}
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static bool needsReferenceType(const DbgVariableLocation &Loc) {
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return Loc.LoadChain.size() == 2 && Loc.LoadChain.back() == 0;
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}
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void CodeViewDebug::calculateRanges(
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LocalVariable &Var, const DbgValueHistoryMap::InstrRanges &Ranges) {
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const TargetRegisterInfo *TRI = Asm->MF->getSubtarget().getRegisterInfo();
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// calculate the definition ranges.
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// Calculate the definition ranges.
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for (auto I = Ranges.begin(), E = Ranges.end(); I != E; ++I) {
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const InsnRange &Range = *I;
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const MachineInstr *DVInst = Range.first;
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@ -965,39 +973,37 @@ void CodeViewDebug::calculateRanges(
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if (!Location)
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continue;
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// Because we cannot express DW_OP_deref in CodeView directly,
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// we use a trick: we encode the type as a reference to the
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// real type.
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if (Var.Deref) {
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// When we're encoding the type as a reference to the original type,
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// we need to remove a level of indirection from incoming locations.
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// E.g. [RSP+8] with DW_OP_deref becomes [RSP+8],
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// and [RCX+0] without DW_OP_deref becomes RCX.
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if (!Location->Deref) {
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if (Location->InMemory)
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Location->InMemory = false;
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else
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continue;
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}
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} else if (Location->Deref) {
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// We've encountered a Deref range when we had not applied the
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// reference encoding. Start over using reference encoding.
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Var.Deref = true;
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// CodeView can only express variables in register and variables in memory
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// at a constant offset from a register. However, for variables passed
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// indirectly by pointer, it is common for that pointer to be spilled to a
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// stack location. For the special case of one offseted load followed by a
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// zero offset load (a pointer spilled to the stack), we change the type of
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// the local variable from a value type to a reference type. This tricks the
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// debugger into doing the load for us.
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if (Var.UseReferenceType) {
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// We're using a reference type. Drop the last zero offset load.
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if (canUseReferenceType(*Location))
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Location->LoadChain.pop_back();
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else
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continue;
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} else if (needsReferenceType(*Location)) {
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// This location can't be expressed without switching to a reference type.
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// Start over using that.
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Var.UseReferenceType = true;
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Var.DefRanges.clear();
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calculateRanges(Var, Ranges);
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return;
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}
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// If we don't know how to handle this range, skip past it.
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if (Location->Register == 0 || (Location->Offset && !Location->InMemory))
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// We can only handle a register or an offseted load of a register.
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if (Location->Register == 0 || Location->LoadChain.size() > 1)
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continue;
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// Handle the two cases we can handle: indirect in memory and in register.
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{
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LocalVarDefRange DR;
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DR.CVRegister = TRI->getCodeViewRegNum(Location->Register);
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DR.InMemory = Location->InMemory;
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DR.DataOffset = Location->Offset;
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DR.InMemory = !Location->LoadChain.empty();
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DR.DataOffset =
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!Location->LoadChain.empty() ? Location->LoadChain.back() : 0;
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if (Location->FragmentInfo) {
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DR.IsSubfield = true;
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DR.StructOffset = Location->FragmentInfo->OffsetInBits / 8;
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@ -2113,8 +2119,9 @@ void CodeViewDebug::emitLocalVariable(const LocalVariable &Var) {
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Flags |= LocalSymFlags::IsOptimizedOut;
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OS.AddComment("TypeIndex");
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TypeIndex TI = Var.Deref ? getTypeIndexForReferenceTo(Var.DIVar->getType())
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: getCompleteTypeIndex(Var.DIVar->getType());
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TypeIndex TI = Var.UseReferenceType
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? getTypeIndexForReferenceTo(Var.DIVar->getType())
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: getCompleteTypeIndex(Var.DIVar->getType());
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OS.EmitIntValue(TI.getIndex(), 4);
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OS.AddComment("Flags");
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OS.EmitIntValue(static_cast<uint16_t>(Flags), 2);
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@ -94,7 +94,7 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
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struct LocalVariable {
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const DILocalVariable *DIVar = nullptr;
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SmallVector<LocalVarDefRange, 1> DefRanges;
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bool Deref = false;
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bool UseReferenceType = false;
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};
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struct InlineSite {
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@ -34,8 +34,6 @@ DbgVariableLocation::extractFromMachineInstruction(
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if (!Instruction.getOperand(0).isReg())
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return None;
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Location.Register = Instruction.getOperand(0).getReg();
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Location.InMemory = Instruction.getOperand(1).isImm();
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Location.Deref = false;
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Location.FragmentInfo.reset();
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// We only handle expressions generated by DIExpression::appendOffset,
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// which doesn't require a full stack machine.
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@ -67,7 +65,8 @@ DbgVariableLocation::extractFromMachineInstruction(
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Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
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break;
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case dwarf::DW_OP_deref:
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Location.Deref = true;
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Location.LoadChain.push_back(Offset);
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Offset = 0;
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break;
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default:
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return None;
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@ -75,7 +74,12 @@ DbgVariableLocation::extractFromMachineInstruction(
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++Op;
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}
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Location.Offset = Offset;
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// Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
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// instruction.
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// FIXME: Replace these with DIExpression.
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if (Instruction.isIndirectDebugValue())
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Location.LoadChain.push_back(Offset);
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return Location;
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}
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@ -30,19 +30,12 @@ class MachineModuleInfo;
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/// Represents the location at which a variable is stored.
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struct DbgVariableLocation {
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/// Offset relative to base register.
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int64_t Offset;
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/// Base register.
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unsigned Register;
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/// If false, Register is the location. If true,
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/// Register+Offset point at the location.
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unsigned InMemory : 1;
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/// If false, the location holds the variable's value.
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/// If true, the location holds the variable's address.
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unsigned Deref : 1;
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/// Chain of offsetted loads necessary to load the value if it lives in
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/// memory. Every load except for the last is pointer-sized.
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SmallVector<int64_t, 1> LoadChain;
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/// Present if the location is part of a larger variable.
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llvm::Optional<llvm::DIExpression::FragmentInfo> FragmentInfo;
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@ -195,7 +195,7 @@ body: |
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CFI_INSTRUCTION offset %esi, -8
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%esi = MOV32rm %esp, 1, _, 8, _ :: (load 4 from %fixed-stack.2)
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DBG_VALUE %esp, 0, !26, !10, debug-location !25
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DBG_VALUE %esp, 0, !23, !11, debug-location !25
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DBG_VALUE %esp, 0, !23, !DIExpression(DW_OP_plus_uconst, 8, DW_OP_deref), debug-location !25
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CALLpcrel32 @getString, csr_32, implicit %esp, implicit-def %esp, implicit-def %eax, debug-location !29
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%ecx = MOV32rm %eax, 1, _, 0, _, debug-location !29 :: (dereferenceable load 4 from %ir.1)
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%edx = MOV32rm %eax, 1, _, 4, _, debug-location !29 :: (dereferenceable load 4 from %ir.1 + 4)
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@ -246,7 +246,7 @@ body: |
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bb.0.entry:
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%eax = MOV32rm %esp, 1, _, 4, _ :: (load 4 from %fixed-stack.1)
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%eax = MOV32rm killed %eax, 1, _, 0, _, debug-location !34 :: (load 4 from %ir.0)
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DBG_VALUE debug-use %eax, 0, !35, !28, debug-location !34
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DBG_VALUE debug-use %eax, 0, !35, !DIExpression(DW_OP_constu, 4, DW_OP_minus), debug-location !34
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%eax = ADD32rm killed %eax, %esp, 1, _, 8, _, implicit-def dead %eflags, debug-location !36 :: (load 4 from %fixed-stack.0)
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RET 0, %eax, debug-location !36
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