[ObjC][DWARF] Emit DW_AT_APPLE_objc_direct for methods marked as __attribute__((objc_direct))

[teemperor]

Summary

With DWARF5 it is no longer possible to distinguish normal methods and methods with __attribute__((objc_direct)) by just looking at the debug information
as they are both now children of the of the DW_TAG_structure_type that defines them (before only the __attribute__((objc_direct)) methods were children).

This means that in LLDB we are no longer able to create a correct Clang AST of a module by just looking at the debug information. Instead we would
need to call the Objective-C runtime to see which of the methods have a __attribute__((objc_direct)) and then add the attribute to our own Clang AST
depending on what the runtime returns. This would mean that we either let the module AST be dependent on the Objective-C runtime (which doesn't
seem right) or we retroactively add the missing attribute to the imported AST in our expressions.

A third option is to annotate methods with __attribute__((objc_direct)) as DW_AT_APPLE_objc_direct which is what this patch implements. This way
LLDB doesn't have to call the runtime for any __attribute__((objc_direct)) method and the AST in our module will already be correct when we create it.

[aprantl]

llvm/include/llvm/IR/DebugInfoFlags.def

93

I think it would be good to leave a gap for https://reviews.llvm.org/D68117 here.
@SouraVX what's the latest plan for representing deleted/defaulted?

llvm/test/DebugInfo/X86/objc_direct.ll

48

Could we make do in this test without all the ObjC metadata?

82

Please remove all quoted attributes, they cause trouble for maintaining the test in the future and usually aren't needed.

[aprantl]

Looks pretty good, thanks!

[teemperor]

• Removed Objective-C metadata from LLVM test.
• Removed quoted attributes.
• Update DebugInfoFlags.def to be compatible with D68117 assuming probinson are applied there.

[aprantl]

Thanks!

It would be nice to further manually reduce the IR testcase by stripping out any metadata that isn't needed. Otherwise this LGTM

[teemperor]

• Further reduced test case.

[aprantl]

Thanks. This is good to go!

clang/lib/CodeGen/CGDebugInfo.cpp

llvm::DISubprogram *CGDebugInfo::getObjCMethodDeclaration(
 
   const auto *OMD = dyn_cast<ObjCMethodDecl>(D);
   if (!OMD)
     return nullptr;
 
   if (CGM.getCodeGenOpts().DwarfVersion < 5 && !OMD->isDirectMethod())
     return nullptr;
 
+  if (OMD->isDirectMethod())
+    SPFlags |= llvm::DISubprogram::SPFlagObjCDirect;
+
   // Starting with DWARF V5 method declarations are emitted as children of
   // the interface type.
   auto *ID = dyn_cast_or_null<ObjCInterfaceDecl>(D->getDeclContext());
   if (!ID)
     ID = OMD->getClassInterface();
   if (!ID)
     return nullptr;
   QualType QTy(ID->getTypeForDecl(), 0);

clang/test/CodeGenObjC/debug-info-direct-method.m

 // RUN: %clang_cc1 -dwarf-version=5 -emit-llvm -debug-info-kind=limited -w -triple x86_64-apple-darwin10 %s -o - | FileCheck %s
 // RUN: %clang_cc1 -dwarf-version=4 -emit-llvm -debug-info-kind=limited -w -triple x86_64-apple-darwin10 %s -o - | FileCheck %s
+// RUN: %clang_cc1 -dwarf-version=5 -emit-llvm -debug-info-kind=limited -w -triple x86_64-apple-darwin10 %s -o - -DDISABLE_DIRECT | FileCheck --check-prefix=CHECK-DISABLED %s
 
 __attribute__((objc_root_class))
 @interface Root
 @end
 
 @implementation Root
-- (int)getInt __attribute__((objc_direct)) {
+- (int)getInt
+#ifndef DISABLE_DIRECT
+ __attribute__((objc_direct))
+#endif
+{
   return 42;
 }
 @end
 
 // Test that objc_direct methods are always (even in DWARF < 5) emitted
 // as members of their containing class.
 
 // CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "Root",
 // CHECK-SAME:             elements: ![[MEMBERS:[0-9]+]],
 // CHECK-SAME:             runtimeLang: DW_LANG_ObjC)
 // CHECK: ![[MEMBERS]] = !{![[GETTER:[0-9]+]]}
 // CHECK: ![[GETTER]] = !DISubprogram(name: "-[Root getInt]",
+// CHECK-SAME: spFlags: DISPFlagObjCDirect
+
+// CHECK-DISABLED-NOT: DISPFlagObjCDirect

llvm/include/llvm/BinaryFormat/Dwarf.def

 HANDLE_DW_AT(0x3fe6, APPLE_runtime_class, 0, APPLE)
 HANDLE_DW_AT(0x3fe7, APPLE_omit_frame_ptr, 0, APPLE)
 HANDLE_DW_AT(0x3fe8, APPLE_property_name, 0, APPLE)
 HANDLE_DW_AT(0x3fe9, APPLE_property_getter, 0, APPLE)
 HANDLE_DW_AT(0x3fea, APPLE_property_setter, 0, APPLE)
 HANDLE_DW_AT(0x3feb, APPLE_property_attribute, 0, APPLE)
 HANDLE_DW_AT(0x3fec, APPLE_objc_complete_type, 0, APPLE)
 HANDLE_DW_AT(0x3fed, APPLE_property, 0, APPLE)
+HANDLE_DW_AT(0x3fee, APPLE_objc_direct, 0, APPLE)
 
 // Attribute form encodings.
 HANDLE_DW_FORM(0x01, addr, 2, DWARF)
 HANDLE_DW_FORM(0x03, block2, 2, DWARF)
 HANDLE_DW_FORM(0x04, block4, 2, DWARF)
 HANDLE_DW_FORM(0x05, data2, 2, DWARF)
 HANDLE_DW_FORM(0x06, data4, 2, DWARF)
 HANDLE_DW_FORM(0x07, data8, 2, DWARF)

llvm/include/llvm/IR/DebugInfoFlags.def

 HANDLE_DISP_FLAG((1u << 4), Optimized)
 HANDLE_DISP_FLAG((1u << 5), Pure)
 HANDLE_DISP_FLAG((1u << 6), Elemental)
 HANDLE_DISP_FLAG((1u << 7), Recursive)
 HANDLE_DISP_FLAG((1u << 8), MainSubprogram)
 // May also utilize this Flag in future, when adding support
 // for defaulted functions
 HANDLE_DISP_FLAG((1u << 9), Deleted)
+HANDLE_DISP_FLAG((1u << 11), ObjCDirect)
 
 #ifdef DISP_FLAG_LARGEST_NEEDED
 // Intended to be used with ADT/BitmaskEnum.h.
 // NOTE: Always must be equal to largest flag, check this when adding new flags.
-HANDLE_DISP_FLAG((1 << 9), Largest)
+HANDLE_DISP_FLAG((1 << 11), Largest)
 #undef DISP_FLAG_LARGEST_NEEDED
 #endif
 
 #undef HANDLE_DI_FLAG
 #undef HANDLE_DISP_FLAG

llvm/include/llvm/IR/DebugInfoMetadata.h

public:
   bool isExplicit() const { return getFlags() & FlagExplicit; }
   bool isPrototyped() const { return getFlags() & FlagPrototyped; }
   bool areAllCallsDescribed() const {
     return getFlags() & FlagAllCallsDescribed;
   }
   bool isPure() const { return getSPFlags() & SPFlagPure; }
   bool isElemental() const { return getSPFlags() & SPFlagElemental; }
   bool isRecursive() const { return getSPFlags() & SPFlagRecursive; }
+  bool isObjCDirect() const { return getSPFlags() & SPFlagObjCDirect; }
 
   /// Check if this is deleted member function.
   ///
   /// Return true if this subprogram is a C++11 special
   /// member function declared deleted.
   bool isDeleted() const { return getSPFlags() & SPFlagDeleted; }
 
   /// Check if this is reference-qualified.

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

void DwarfUnit::applySubprogramAttributes(const DISubprogram *SP, DIE &SPDie,
   // Add the prototype if we have a prototype and we have a C like
   // language.
   uint16_t Language = getLanguage();
   if (SP->isPrototyped() &&
       (Language == dwarf::DW_LANG_C89 || Language == dwarf::DW_LANG_C99 ||
        Language == dwarf::DW_LANG_ObjC))
     addFlag(SPDie, dwarf::DW_AT_prototyped);
 
+  if (SP->isObjCDirect())
+    addFlag(SPDie, dwarf::DW_AT_APPLE_objc_direct);
+
   unsigned CC = 0;
   DITypeRefArray Args;
   if (const DISubroutineType *SPTy = SP->getType()) {
     Args = SPTy->getTypeArray();
     CC = SPTy->getCC();
   }
 
   // Add a DW_AT_calling_convention if this has an explicit convention.

llvm/test/DebugInfo/X86/objc_direct.ll

+; RUN: llc < %s -filetype=obj -o %t
+; RUN: llvm-dwarfdump -v %t | FileCheck %s
+
+; Source code to regenerate:
+; __attribute__((objc_root_class))
+; @interface Root
+; - (int)direct_method __attribute__((objc_direct));
+; @end
+;
+; @implementation Root
+; - (int)direct_method __attribute__((objc_direct)) {
+;   return 42;
+; }
+; @end
+;
+; clang -O0 -g -gdwarf-5 direct.m -c
+
+; CHECK: DW_TAG_subprogram [3]
+; CHECK: DW_AT_APPLE_objc_direct
+; CHECK-SAME: DW_FORM_flag_present
+; CHECK: DW_TAG_formal_parameter [4]
+
+; ModuleID = 'direct.bc'
+source_filename = "direct.m"
+
+%0 = type opaque
+
+define hidden i32 @"\01-[Root direct_method]"(%0* %self, i8* %_cmd) {
+entry:
+  %retval = alloca i32, align 4
+  %0 = load i32, i32* %retval, align 4
+  ret i32 %0
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!19, !20}
+!llvm.ident = !{}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_ObjC, file: !1, producer: "clang version 10.0.0 (https://github.com/llvm/llvm-project d6b2f33e2b6338d24cf756ba220939aecc81210d)", isOptimized: false, runtimeVersion: 2, emissionKind: FullDebug, enums: !2, retainedTypes: !3, nameTableKind: None)
+!1 = !DIFile(filename: "direct.m", directory: "/", checksumkind: CSK_MD5, checksum: "6b49fad130344b0011fc0eef65949390")
+!2 = !{}
+!3 = !{!4}
+!4 = !DICompositeType(tag: DW_TAG_structure_type, name: "Root", scope: !1, file: !1, line: 2, flags: DIFlagObjcClassComplete, elements: !5, runtimeLang: DW_LANG_ObjC)
+!5 = !{!6}
+!6 = !DISubprogram(name: "-[Root direct_method]", scope: !4, file: !1, line: 7, type: !7, scopeLine: 7, flags: DIFlagPrototyped, spFlags: DISPFlagObjCDirect, retainedNodes: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{!9, !10, !11}
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !4, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!11 = !DIDerivedType(tag: DW_TAG_typedef, name: "SEL", file: !1, baseType: !12, flags: DIFlagArtificial)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!13 = !DICompositeType(tag: DW_TAG_structure_type, name: "objc_selector", file: !1, flags: DIFlagFwdDecl)
+!19 = !{i32 7, !"Dwarf Version", i32 5}
+!20 = !{i32 2, !"Debug Info Version", i32 3}