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

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.

Reviewers: aprantl, SouraVX

Reviewed By: aprantl

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm, #debug-info

Differential Revision: https://reviews.llvm.org/D71201

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -3495,6 +3495,9 @@ llvm::DISubprogram *CGDebugInfo::getObjCMethodDeclaration(
   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());

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

@@ -1,12 +1,17 @@
 // 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
@@ -19,3 +24,6 @@ __attribute__((objc_root_class))
 // 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

@@ -421,6 +421,7 @@ 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)

llvm/include/llvm/IR/DebugInfoFlags.def

@@ -90,11 +90,12 @@ 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
 

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -1758,6 +1758,7 @@ public:
   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.
   ///

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -1233,6 +1233,9 @@ void DwarfUnit::applySubprogramAttributes(const DISubprogram *SP, DIE &SPDie,
        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()) {

llvm/test/DebugInfo/X86/objc_direct.ll

@@ -0,0 +1,54 @@
+; 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}