Add a -reflection-metadata-for-debugger-only flag that emits reflection metadata but does not link them from runtime data structures (#40853)

Author: kubamracek

include/swift/AST/IRGenOptions.h

@@ -87,6 +87,13 @@ enum class SwiftAsyncFramePointerKind : unsigned {
    Never,  // Don't emit Swift async extended frame info.
 };
 
+enum class ReflectionMetadataMode : unsigned {
+  None,         ///< Don't emit reflection metadata at all.
+  DebuggerOnly, ///< Emit reflection metadata for the debugger, don't link them
+                ///  into runtime metadata and don't force them to stay alive.
+  Runtime,      ///< Make reflection metadata fully available.
+};
+
 using clang::PointerAuthSchema;
 
 struct PointerAuthOptions : clang::PointerAuthOptions {
@@ -295,7 +302,7 @@ class IRGenOptions {
   unsigned ValueNames : 1;
 
   /// Emit nominal type field metadata.
-  unsigned EnableReflectionMetadata : 1;
+  ReflectionMetadataMode ReflectionMetadata : 2;
 
   /// Emit names of struct stored properties and enum cases.
   unsigned EnableReflectionNames : 1;
@@ -423,7 +430,7 @@ class IRGenOptions {
         LLVMLTOKind(IRGenLLVMLTOKind::None),
         SwiftAsyncFramePointer(SwiftAsyncFramePointerKind::Auto),
         HasValueNamesSetting(false),
-        ValueNames(false), EnableReflectionMetadata(true),
+        ValueNames(false), ReflectionMetadata(ReflectionMetadataMode::Runtime),
         EnableReflectionNames(true), EnableAnonymousContextMangledNames(false),
         ForcePublicLinkage(false), LazyInitializeClassMetadata(false),
         LazyInitializeProtocolConformances(false),

include/swift/Option/FrontendOptions.td

@@ -455,6 +455,9 @@ def enable_anonymous_context_mangled_names :
 def disable_reflection_metadata : Flag<["-"], "disable-reflection-metadata">,
   HelpText<"Disable emission of reflection metadata for nominal types">;
 
+def reflection_metadata_for_debugger_only : Flag<["-"], "reflection-metadata-for-debugger-only">,
+  HelpText<"Emit reflection metadata for debugger only, don't make them available at runtime">;
+
 def disable_reflection_names : Flag<["-"], "disable-reflection-names">,
   HelpText<"Disable emission of names of stored properties and enum cases in"
            "reflection metadata">;

lib/Frontend/CompilerInvocation.cpp

@@ -2043,10 +2043,15 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
   }
 
   if (Args.hasArg(OPT_disable_reflection_metadata)) {
-    Opts.EnableReflectionMetadata = false;
+    Opts.ReflectionMetadata = ReflectionMetadataMode::None;
     Opts.EnableReflectionNames = false;
   }
 
+  if (Args.hasArg(OPT_reflection_metadata_for_debugger_only)) {
+    Opts.ReflectionMetadata = ReflectionMetadataMode::DebuggerOnly;
+    Opts.EnableReflectionNames = true;
+  }
+
   if (Args.hasArg(OPT_enable_anonymous_context_mangled_names))
     Opts.EnableAnonymousContextMangledNames = true;
 

lib/IRGen/GenMeta.cpp

@@ -1488,11 +1488,12 @@ namespace {
     void maybeAddResilientSuperclass() { }
 
     void addReflectionFieldDescriptor() {
-      if (!IGM.IRGen.Opts.EnableReflectionMetadata) {
+      if (IGM.IRGen.Opts.ReflectionMetadata !=
+          ReflectionMetadataMode::Runtime) {
         B.addInt32(0);
         return;
       }
-    
+
       IGM.IRGen.noteUseOfFieldDescriptor(getType());
 
       B.addRelativeAddress(IGM.getAddrOfReflectionFieldDescriptor(
@@ -1566,7 +1567,8 @@ namespace {
     void maybeAddResilientSuperclass() { }
 
     void addReflectionFieldDescriptor() {
-      if (!IGM.IRGen.Opts.EnableReflectionMetadata) {
+      if (IGM.IRGen.Opts.ReflectionMetadata !=
+          ReflectionMetadataMode::Runtime) {
         B.addInt32(0);
         return;
       }
@@ -1723,7 +1725,8 @@ namespace {
     void addReflectionFieldDescriptor() {
       // Classes are always reflectable, unless reflection is disabled or this
       // is a foreign class.
-      if (!IGM.IRGen.Opts.EnableReflectionMetadata ||
+      if ((IGM.IRGen.Opts.ReflectionMetadata !=
+           ReflectionMetadataMode::Runtime) ||
           getType()->isForeign()) {
         B.addInt32(0);
         return;

lib/IRGen/GenReflection.cpp

@@ -623,7 +623,12 @@ class ReflectionMetadataBuilder {
 
     var->setSection(section);
 
-    IGM.addUsedGlobal(var);
+    // Only mark the reflection record as used when emitting for the runtime.
+    // In ReflectionMetadataMode::DebuggerOnly mode we want to allow the linker
+    // to remove/dead-strip these.
+    if (IGM.IRGen.Opts.ReflectionMetadata == ReflectionMetadataMode::Runtime) {
+      IGM.addUsedGlobal(var);
+    }
 
     disableAddressSanitizer(IGM, var);
 
@@ -1335,7 +1340,7 @@ llvm::Constant *IRGenModule::getAddrOfFieldName(StringRef Name) {
 llvm::Constant *
 IRGenModule::getAddrOfBoxDescriptor(SILType BoxedType,
                                     CanGenericSignature genericSig) {
-  if (!IRGen.Opts.EnableReflectionMetadata)
+  if (IRGen.Opts.ReflectionMetadata != ReflectionMetadataMode::Runtime)
     return llvm::Constant::getNullValue(CaptureDescriptorPtrTy);
 
   BoxDescriptorBuilder builder(*this, BoxedType, genericSig);
@@ -1350,7 +1355,7 @@ IRGenModule::getAddrOfCaptureDescriptor(SILFunction &Caller,
                                         CanSILFunctionType SubstCalleeType,
                                         SubstitutionMap Subs,
                                         const HeapLayout &Layout) {
-  if (!IRGen.Opts.EnableReflectionMetadata)
+  if (IRGen.Opts.ReflectionMetadata != ReflectionMetadataMode::Runtime)
     return llvm::Constant::getNullValue(CaptureDescriptorPtrTy);
 
   if (CaptureDescriptorBuilder::hasOpenedExistential(OrigCalleeType, Layout))
@@ -1369,7 +1374,7 @@ emitAssociatedTypeMetadataRecord(const RootProtocolConformance *conformance) {
   if (!normalConf)
     return;
 
-  if (!IRGen.Opts.EnableReflectionMetadata)
+  if (IRGen.Opts.ReflectionMetadata != ReflectionMetadataMode::Runtime)
     return;
 
   SmallVector<std::pair<StringRef, CanType>, 2> AssociatedTypes;
@@ -1428,7 +1433,7 @@ void IRGenerator::emitBuiltinReflectionMetadata() {
 }
 
 void IRGenModule::emitFieldDescriptor(const NominalTypeDecl *D) {
-  if (!IRGen.Opts.EnableReflectionMetadata)
+  if (IRGen.Opts.ReflectionMetadata == ReflectionMetadataMode::None)
     return;
 
   auto T = D->getDeclaredTypeInContext()->getCanonicalType();

test/IRGen/reflection-metadata-for-debugger-only.swift

@@ -0,0 +1,41 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -module-name main %s -emit-ir | %FileCheck %s --check-prefix=CHECK-REFL
+// RUN: %target-swift-frontend -module-name main %s -emit-ir -reflection-metadata-for-debugger-only | %FileCheck %s --check-prefix=CHECK-REFLDEBUG
+// RUN: %target-swift-frontend -module-name main %s -emit-ir -disable-reflection-metadata | %FileCheck %s --check-prefix=CHECK-NOREFL
+
+public class Generic<T> {
+  public func m1(t: T) -> T { return t }
+  public func m2(t: T) -> T { return t }
+}
+
+protocol MyProtocol {
+  associatedtype T
+  func foo() -> T
+}
+
+public struct MyStruct<T>: MyProtocol {
+  func foo() -> T { fatalError() }
+}
+
+// CHECK-REFL: @"$s4main8MyStructVyxGAA0B8ProtocolAAMA"
+// CHECK-REFL: @"$s4main7GenericCMn" = {{.*}} @"$s4main7GenericCMF" {{.*}}
+// CHECK-REFL: @"$s4main7GenericCMF" =
+// CHECK-REFL: @"$s4main10MyProtocol_pMF" =
+// CHECK-REFL: @"$s4main8MyStructVMn" = {{.*}} @"$s4main8MyStructVMF" {{.*}}
+// CHECK-REFL: @"$s4main8MyStructVMF" =
+
+// CHECK-REFLDEBUG-NOT: @"$s4main8MyStructVyxGAA0B8ProtocolAAMA"
+// CHECK-REFLDEBUG: @"$s4main7GenericCMn" =
+// CHECK-REFLDEBUG-NOT: @"$s4main7GenericCMF"
+// CHECK-REFLDEBUG-SAME: , align 4
+// CHECK-REFLDEBUG: @"$s4main7GenericCMF" =
+// CHECK-REFLDEBUG: @"$s4main10MyProtocol_pMF" =
+// CHECK-REFLDEBUG: @"$s4main8MyStructVMn" =
+// CHECK-REFLDEBUG-NOT: @"$s4main8MyStructVMF"
+// CHECK-REFLDEBUG-SAME: , align 4
+// CHECK-REFLDEBUG: @"$s4main8MyStructVMF" =
+
+// CHECK-NOREFL-NOT: @"$s4main8MyStructVyxGAA0B8ProtocolAAMA"
+// CHECK-NOREFL-NOT: @"$s4main10MyProtocol_pMF"
+// CHECK-NOREFL-NOT: @"$s4main7GenericCMF"
+// CHECK-NOREFL-NOT: @"$s4main8MyStructVMF"