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[Reflection] Hoist computation of error existentials to the reader. #18242

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Merged
merged 1 commit into from
Jul 26, 2018
Merged

[Reflection] Hoist computation of error existentials to the reader. #18242

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68 changes: 10 additions & 58 deletions include/swift/Reflection/ReflectionContext.h
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Original file line number Diff line number Diff line change
Expand Up @@ -77,11 +77,12 @@ class ReflectionContext
public:
using super::getBuilder;
using super::readDemanglingForContextDescriptor;
using super::readIsaMask;
using super::readTypeFromMetadata;
using super::readGenericArgFromMetadata;
using super::readIsaMask;
using super::readMetadataAndValueErrorExistential;
using super::readMetadataAndValueOpaqueExistential;
using super::readMetadataFromInstance;
using super::readTypeFromMetadata;
using typename super::StoredPointer;

explicit ReflectionContext(std::shared_ptr<MemoryReader> reader)
Expand Down Expand Up @@ -497,70 +498,21 @@ class ReflectionContext
return true;
}
case RecordKind::ErrorExistential: {
// We have a pointer to an error existential, which is always heap object.

auto MetadataAddress
= readMetadataFromInstance(ExistentialAddress.getAddressData());

if (!MetadataAddress)
auto OptMetaAndValue =
readMetadataAndValueErrorExistential(ExistentialAddress);
if (!OptMetaAndValue)
return false;

bool isObjC = false;

// If we can determine the Objective-C class name, this is probably an
// error existential with NSError-compatible layout.
std::string ObjCClassName;
if (readObjCClassName(*MetadataAddress, ObjCClassName)) {
if (ObjCClassName == "_SwiftNativeNSError")
isObjC = true;
} else {
// Otherwise, we can check to see if this is a class metadata with the
// kind value's least significant bit set, which indicates a pure
// Swift class.
auto Meta = readMetadata(*MetadataAddress);
auto ClassMeta = dyn_cast<TargetClassMetadata<Runtime>>(Meta);
if (!ClassMeta)
return false;

isObjC = ClassMeta->isPureObjC();
}

// In addition to the isa pointer and two 32-bit reference counts, if the
// error existential is layout-compatible with NSError, we also need to
// skip over its three word-sized fields: the error code, the domain,
// and userInfo.
StoredPointer InstanceMetadataAddressAddress
= ExistentialAddress.getAddressData() +
(isObjC ? 5 : 2) * sizeof(StoredPointer);

// We need to get the instance's alignment info so we can get the exact
// offset of the start of its data in the class.
auto InstanceMetadataAddress =
readMetadataFromInstance(InstanceMetadataAddressAddress);
if (!InstanceMetadataAddress)
return false;
RemoteAddress InstanceMetadataAddress = OptMetaAndValue->first;
RemoteAddress InstanceAddress = OptMetaAndValue->second;

auto InstanceTR = readTypeFromMetadata(*InstanceMetadataAddress);
auto InstanceTR =
readTypeFromMetadata(InstanceMetadataAddress.getAddressData());
if (!InstanceTR)
return false;

auto InstanceTI = getTypeInfo(InstanceTR);
if (!InstanceTI)
return false;

// Now we need to skip over the instance metadata pointer and instance's
// conformance pointer for Swift.Error.
StoredPointer InstanceAddress = InstanceMetadataAddressAddress +
2 * sizeof(StoredPointer);

// Round up to alignment, and we have the start address of the
// instance payload.
auto Alignment = InstanceTI->getAlignment();
InstanceAddress += Alignment - InstanceAddress % Alignment;

*OutInstanceTR = InstanceTR;
*OutInstanceAddress = RemoteAddress(InstanceAddress);

return true;
}
default:
Expand Down
69 changes: 68 additions & 1 deletion include/swift/Remote/MetadataReader.h
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Original file line number Diff line number Diff line change
Expand Up @@ -265,7 +265,8 @@ class MetadataReader {
}

/// Given a pointer to the metadata, attempt to read the value
/// witness table.
/// witness table. Note that it's not safe to access any non-mandatory
/// members of the value witness table, like extra inhabitants or enum members.
llvm::Optional<TargetValueWitnessTable<Runtime>>
readValueWitnessTable(StoredPointer MetadataAddress) {
// The value witness table pointer is at offset -1 from the metadata
Expand All @@ -283,6 +284,72 @@ class MetadataReader {
return VWT;
}

/// Given a pointer to a known-error existential, attempt to discover the
/// pointer to its metadata address and its value address.
llvm::Optional<std::pair<RemoteAddress, RemoteAddress>>
readMetadataAndValueErrorExistential(RemoteAddress ExistentialAddress) {
// An pointer to an error existential is always an heap object.
auto MetadataAddress =
readMetadataFromInstance(ExistentialAddress.getAddressData());
if (!MetadataAddress)
return llvm::None;

bool isObjC = false;

// If we can determine the Objective-C class name, this is probably an
// error existential with NSError-compatible layout.
std::string ObjCClassName;
if (readObjCClassName(*MetadataAddress, ObjCClassName)) {
if (ObjCClassName == "_SwiftNativeNSError")
isObjC = true;
} else {
// Otherwise, we can check to see if this is a class metadata with the
// kind value's least significant bit set, which indicates a pure
// Swift class.
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Wait, does this happen? And if so, when? Is it just when ObjCInterop is disabled, because I feel like that's something that we ought to be able to check for (and arguably ought to be part of the Runtime template argument).

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This doesn't seem to ever happen (I tried to put an assertion and the tests still pass). I might consider removing this but I want to try a little harder to see whether I can exercise this.

auto Meta = readMetadata(*MetadataAddress);
auto ClassMeta = dyn_cast<TargetClassMetadata<Runtime>>(Meta);
if (!ClassMeta)
return llvm::None;

isObjC = ClassMeta->isPureObjC();
}

// In addition to the isa pointer and two 32-bit reference counts, if the
// error existential is layout-compatible with NSError, we also need to
// skip over its three word-sized fields: the error code, the domain,
// and userInfo.
StoredPointer InstanceMetadataAddressAddress =
ExistentialAddress.getAddressData() +
(isObjC ? 5 : 2) * sizeof(StoredPointer);
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Hmm. It'd be nice to just have a type for this structure.

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Indeed. Will try to introduce one.


// We need to get the instance's alignment info so we can get the exact
// offset of the start of its data in the class.
auto InstanceMetadataAddress =
readMetadataFromInstance(InstanceMetadataAddressAddress);
if (!InstanceMetadataAddress)
return llvm::None;

// Read the value witness table.
auto VWT = readValueWitnessTable(*InstanceMetadataAddress);
if (!VWT)
return llvm::None;

// Now we need to skip over the instance metadata pointer and instance's
// conformance pointer for Swift.Error.
StoredPointer InstanceAddress =
InstanceMetadataAddressAddress + 2 * sizeof(StoredPointer);

// Round up to alignment, and we have the start address of the
// instance payload.
auto AlignmentMask = VWT->getAlignmentMask();
auto Offset = (sizeof(HeapObject) + AlignmentMask) & ~AlignmentMask;
InstanceAddress += Offset;

return llvm::Optional<std::pair<RemoteAddress, RemoteAddress>>(
{RemoteAddress(*InstanceMetadataAddress),
RemoteAddress(InstanceAddress)});
}

/// Given a known-opaque existential, attemp to discover the pointer to its
/// metadata address and its value.
llvm::Optional<std::pair<RemoteAddress, RemoteAddress>>
Expand Down