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IRGen: Only mark field offset globals as constant if they won't be updated at runtime #20206

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Merged
merged 1 commit into from
Nov 1, 2018
Merged

IRGen: Only mark field offset globals as constant if they won't be updated at runtime #20206

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8 changes: 4 additions & 4 deletions lib/IRGen/GenClass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -993,17 +993,17 @@ void IRGenModule::emitClassDecl(ClassDecl *D) {
SILType selfType = getSelfType(D);
auto &classTI = getTypeInfo(selfType).as<ClassTypeInfo>();

// FIXME: For now, always use the fragile layout when emitting metadata.
// Use the fragile layout when emitting metadata.
auto &fragileLayout =
classTI.getClassLayout(*this, selfType, /*forBackwardDeployment=*/true);

// ... but still compute the resilient layout for better test coverage.
// The resilient layout tells us what parts of the metadata can be
// updated at runtime by the Objective-C metadata update callback.
auto &resilientLayout =
classTI.getClassLayout(*this, selfType, /*forBackwardDeployment=*/false);
(void) resilientLayout;

// Emit the class metadata.
emitClassMetadata(*this, D, fragileLayout);
emitClassMetadata(*this, D, fragileLayout, resilientLayout);

IRGen.addClassForEagerInitialization(D);

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33 changes: 23 additions & 10 deletions lib/IRGen/GenMeta.cpp
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Expand Up @@ -2293,9 +2293,10 @@ getAddrOfDestructorFunction(IRGenModule &IGM, ClassDecl *classDecl) {

static void emitFieldOffsetGlobals(IRGenModule &IGM,
ClassDecl *classDecl,
const ClassLayout &classLayout) {
const ClassLayout &fragileLayout,
const ClassLayout &resilientLayout) {
for (auto prop : classDecl->getStoredProperties()) {
auto fieldInfo = classLayout.getFieldAccessAndElement(prop);
auto fieldInfo = fragileLayout.getFieldAccessAndElement(prop);
auto access = fieldInfo.first;
auto element = fieldInfo.second;

Expand Down Expand Up @@ -2323,8 +2324,19 @@ static void emitFieldOffsetGlobals(IRGenModule &IGM,
auto offsetVar = cast<llvm::GlobalVariable>(offsetAddr.getAddress());
offsetVar->setInitializer(fieldOffsetOrZero);

// If we know the offset won't change, make it a constant.
offsetVar->setConstant(access == FieldAccess::ConstantDirect);
// If the offset is constant in the resilient layout, it will not change
// at runtime, and the global can be true const.
//
// If it is constant in the fragile layout only, newer Objective-C
// runtimes will still update them in place, so make sure to check the
// correct layout.
auto resilientInfo = resilientLayout.getFieldAccessAndElement(prop);
if (resilientInfo.first == FieldAccess::ConstantDirect) {
// If it is constant in the resilient layout, it should be constant in
// the fragile layout also.
assert(access == FieldAccess::ConstantDirect);
offsetVar->setConstant(true);
}

break;
}
Expand Down Expand Up @@ -3015,11 +3027,12 @@ static void emitObjCClassSymbol(IRGenModule &IGM,

/// Emit the type metadata or metadata template for a class.
void irgen::emitClassMetadata(IRGenModule &IGM, ClassDecl *classDecl,
const ClassLayout &fieldLayout) {
const ClassLayout &fragileLayout,
const ClassLayout &resilientLayout) {
assert(!classDecl->isForeign());
PrettyStackTraceDecl stackTraceRAII("emitting metadata for", classDecl);

emitFieldOffsetGlobals(IGM, classDecl, fieldLayout);
emitFieldOffsetGlobals(IGM, classDecl, fragileLayout, resilientLayout);

// Set up a dummy global to stand in for the metadata object while we produce
// relative references.
Expand All @@ -3034,28 +3047,28 @@ void irgen::emitClassMetadata(IRGenModule &IGM, ClassDecl *classDecl,
bool canBeConstant;
if (classDecl->isGenericContext()) {
GenericClassMetadataBuilder builder(IGM, classDecl, init,
fieldLayout);
fragileLayout);
builder.layout();
canBeConstant = true;

builder.createMetadataAccessFunction();
} else if (doesClassMetadataRequireRelocation(IGM, classDecl)) {
ResilientClassMetadataBuilder builder(IGM, classDecl, init,
fieldLayout);
fragileLayout);
builder.layout();
canBeConstant = true;

builder.createMetadataAccessFunction();
} else if (doesClassMetadataRequireInitialization(IGM, classDecl)) {
SingletonClassMetadataBuilder builder(IGM, classDecl, init,
fieldLayout);
fragileLayout);
builder.layout();
canBeConstant = builder.canBeConstant();

builder.createMetadataAccessFunction();
} else {
FixedClassMetadataBuilder builder(IGM, classDecl, init,
fieldLayout);
fragileLayout);
builder.layout();
canBeConstant = builder.canBeConstant();

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3 changes: 2 additions & 1 deletion lib/IRGen/GenMeta.h
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Expand Up @@ -52,7 +52,8 @@ namespace irgen {

/// Emit the metadata associated with the given class declaration.
void emitClassMetadata(IRGenModule &IGM, ClassDecl *theClass,
const ClassLayout &fieldLayout);
const ClassLayout &fragileLayout,
const ClassLayout &resilientLayout);

/// Emit the constant initializer of the type metadata candidate for
/// the given foreign class declaration.
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12 changes: 6 additions & 6 deletions test/IRGen/completely_fragile_class_layout.sil
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Expand Up @@ -37,8 +37,8 @@ sil_vtable SubclassOfClassWithResilientField {}

// Field offsets are statically known:
// CHECK-DAG: @"$s31completely_fragile_class_layout23ClassWithResilientFieldC5firstSivpWvd" = hidden constant i64 16, align 8
// CHECK-DAG: @"$s31completely_fragile_class_layout23ClassWithResilientFieldC6second16resilient_struct4SizeVvpWvd" = hidden constant i64 24, align 8
// CHECK-DAG: @"$s31completely_fragile_class_layout23ClassWithResilientFieldC5thirdSivpWvd" = hidden constant i64 40, align 8
// CHECK-DAG: @"$s31completely_fragile_class_layout23ClassWithResilientFieldC6second16resilient_struct4SizeVvpWvd" = hidden global i64 24, align 8
// CHECK-DAG: @"$s31completely_fragile_class_layout23ClassWithResilientFieldC5thirdSivpWvd" = hidden global i64 40, align 8


// RO-data for ClassWithResilientField:
Expand Down Expand Up @@ -91,8 +91,8 @@ public class ClassWithResilientEnum {
sil_vtable ClassWithResilientEnum {}

// Field offsets are statically known:
// CHECK-LABEL: @"$s31completely_fragile_class_layout22ClassWithResilientEnumC5firstAA0hfG7PayloadOvpWvd" = hidden constant i64 16, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout22ClassWithResilientEnumC6seconds4Int8VvpWvd" = hidden constant i64 25, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout22ClassWithResilientEnumC5firstAA0hfG7PayloadOvpWvd" = hidden global i64 16, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout22ClassWithResilientEnumC6seconds4Int8VvpWvd" = hidden global i64 25, align 8


// Make sure extra inhabitants work when reading a legacy layout -- the
Expand All @@ -105,8 +105,8 @@ public class ClassWithResilientRef {
sil_vtable ClassWithResilientRef {}

// Field offsets are statically known:
// CHECK-LABEL: @"$s31completely_fragile_class_layout21ClassWithResilientRefC5first16resilient_struct0gH0VSgvpWvd" = hidden constant i64 16, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout21ClassWithResilientRefC6secondSivpWvd" = hidden constant i64 24, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout21ClassWithResilientRefC5first16resilient_struct0gH0VSgvpWvd" = hidden global i64 16, align 8
// CHECK-LABEL: @"$s31completely_fragile_class_layout21ClassWithResilientRefC6secondSivpWvd" = hidden global i64 24, align 8


// When allocating a class with resiliently-sized fields, we must still load
Expand Down