[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
This commit is contained in:
Reid Kleckner 2017-08-31 15:56:49 +00:00
parent f0e1949722
commit 1e6362c860
5 changed files with 48 additions and 44 deletions

View File

@ -949,11 +949,19 @@ void CodeViewDebug::collectVariableInfoFromMFTable(
}
}
static bool canUseReferenceType(const DbgVariableLocation &Loc) {
return !Loc.LoadChain.empty() && Loc.LoadChain.back() == 0;
}
static bool needsReferenceType(const DbgVariableLocation &Loc) {
return Loc.LoadChain.size() == 2 && Loc.LoadChain.back() == 0;
}
void CodeViewDebug::calculateRanges(
LocalVariable &Var, const DbgValueHistoryMap::InstrRanges &Ranges) {
const TargetRegisterInfo *TRI = Asm->MF->getSubtarget().getRegisterInfo();
// calculate the definition ranges.
// Calculate the definition ranges.
for (auto I = Ranges.begin(), E = Ranges.end(); I != E; ++I) {
const InsnRange &Range = *I;
const MachineInstr *DVInst = Range.first;
@ -965,39 +973,37 @@ void CodeViewDebug::calculateRanges(
if (!Location)
continue;
// Because we cannot express DW_OP_deref in CodeView directly,
// we use a trick: we encode the type as a reference to the
// real type.
if (Var.Deref) {
// When we're encoding the type as a reference to the original type,
// we need to remove a level of indirection from incoming locations.
// E.g. [RSP+8] with DW_OP_deref becomes [RSP+8],
// and [RCX+0] without DW_OP_deref becomes RCX.
if (!Location->Deref) {
if (Location->InMemory)
Location->InMemory = false;
else
continue;
}
} else if (Location->Deref) {
// We've encountered a Deref range when we had not applied the
// reference encoding. Start over using reference encoding.
Var.Deref = true;
// CodeView can only express variables in register and variables in memory
// at a constant offset from a register. However, for variables passed
// indirectly by pointer, it is common for that pointer to be spilled to a
// stack location. For the special case of one offseted load followed by a
// zero offset load (a pointer spilled to the stack), we change the type of
// the local variable from a value type to a reference type. This tricks the
// debugger into doing the load for us.
if (Var.UseReferenceType) {
// We're using a reference type. Drop the last zero offset load.
if (canUseReferenceType(*Location))
Location->LoadChain.pop_back();
else
continue;
} else if (needsReferenceType(*Location)) {
// This location can't be expressed without switching to a reference type.
// Start over using that.
Var.UseReferenceType = true;
Var.DefRanges.clear();
calculateRanges(Var, Ranges);
return;
}
// If we don't know how to handle this range, skip past it.
if (Location->Register == 0 || (Location->Offset && !Location->InMemory))
// We can only handle a register or an offseted load of a register.
if (Location->Register == 0 || Location->LoadChain.size() > 1)
continue;
// Handle the two cases we can handle: indirect in memory and in register.
{
LocalVarDefRange DR;
DR.CVRegister = TRI->getCodeViewRegNum(Location->Register);
DR.InMemory = Location->InMemory;
DR.DataOffset = Location->Offset;
DR.InMemory = !Location->LoadChain.empty();
DR.DataOffset =
!Location->LoadChain.empty() ? Location->LoadChain.back() : 0;
if (Location->FragmentInfo) {
DR.IsSubfield = true;
DR.StructOffset = Location->FragmentInfo->OffsetInBits / 8;
@ -2113,8 +2119,9 @@ void CodeViewDebug::emitLocalVariable(const LocalVariable &Var) {
Flags |= LocalSymFlags::IsOptimizedOut;
OS.AddComment("TypeIndex");
TypeIndex TI = Var.Deref ? getTypeIndexForReferenceTo(Var.DIVar->getType())
: getCompleteTypeIndex(Var.DIVar->getType());
TypeIndex TI = Var.UseReferenceType
? getTypeIndexForReferenceTo(Var.DIVar->getType())
: getCompleteTypeIndex(Var.DIVar->getType());
OS.EmitIntValue(TI.getIndex(), 4);
OS.AddComment("Flags");
OS.EmitIntValue(static_cast<uint16_t>(Flags), 2);

View File

@ -94,7 +94,7 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
struct LocalVariable {
const DILocalVariable *DIVar = nullptr;
SmallVector<LocalVarDefRange, 1> DefRanges;
bool Deref = false;
bool UseReferenceType = false;
};
struct InlineSite {

View File

@ -34,8 +34,6 @@ DbgVariableLocation::extractFromMachineInstruction(
if (!Instruction.getOperand(0).isReg())
return None;
Location.Register = Instruction.getOperand(0).getReg();
Location.InMemory = Instruction.getOperand(1).isImm();
Location.Deref = false;
Location.FragmentInfo.reset();
// We only handle expressions generated by DIExpression::appendOffset,
// which doesn't require a full stack machine.
@ -67,7 +65,8 @@ DbgVariableLocation::extractFromMachineInstruction(
Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
break;
case dwarf::DW_OP_deref:
Location.Deref = true;
Location.LoadChain.push_back(Offset);
Offset = 0;
break;
default:
return None;
@ -75,7 +74,12 @@ DbgVariableLocation::extractFromMachineInstruction(
++Op;
}
Location.Offset = Offset;
// Do one final implicit DW_OP_deref if this was an indirect DBG_VALUE
// instruction.
// FIXME: Replace these with DIExpression.
if (Instruction.isIndirectDebugValue())
Location.LoadChain.push_back(Offset);
return Location;
}

View File

@ -30,19 +30,12 @@ class MachineModuleInfo;
/// Represents the location at which a variable is stored.
struct DbgVariableLocation {
/// Offset relative to base register.
int64_t Offset;
/// Base register.
unsigned Register;
/// If false, Register is the location. If true,
/// Register+Offset point at the location.
unsigned InMemory : 1;
/// If false, the location holds the variable's value.
/// If true, the location holds the variable's address.
unsigned Deref : 1;
/// Chain of offsetted loads necessary to load the value if it lives in
/// memory. Every load except for the last is pointer-sized.
SmallVector<int64_t, 1> LoadChain;
/// Present if the location is part of a larger variable.
llvm::Optional<llvm::DIExpression::FragmentInfo> FragmentInfo;

View File

@ -195,7 +195,7 @@ body: |
CFI_INSTRUCTION offset %esi, -8
%esi = MOV32rm %esp, 1, _, 8, _ :: (load 4 from %fixed-stack.2)
DBG_VALUE %esp, 0, !26, !10, debug-location !25
DBG_VALUE %esp, 0, !23, !11, debug-location !25
DBG_VALUE %esp, 0, !23, !DIExpression(DW_OP_plus_uconst, 8, DW_OP_deref), debug-location !25
CALLpcrel32 @getString, csr_32, implicit %esp, implicit-def %esp, implicit-def %eax, debug-location !29
%ecx = MOV32rm %eax, 1, _, 0, _, debug-location !29 :: (dereferenceable load 4 from %ir.1)
%edx = MOV32rm %eax, 1, _, 4, _, debug-location !29 :: (dereferenceable load 4 from %ir.1 + 4)
@ -246,7 +246,7 @@ body: |
bb.0.entry:
%eax = MOV32rm %esp, 1, _, 4, _ :: (load 4 from %fixed-stack.1)
%eax = MOV32rm killed %eax, 1, _, 0, _, debug-location !34 :: (load 4 from %ir.0)
DBG_VALUE debug-use %eax, 0, !35, !28, debug-location !34
DBG_VALUE debug-use %eax, 0, !35, !DIExpression(DW_OP_constu, 4, DW_OP_minus), debug-location !34
%eax = ADD32rm killed %eax, %esp, 1, _, 8, _, implicit-def dead %eflags, debug-location !36 :: (load 4 from %fixed-stack.0)
RET 0, %eax, debug-location !36