[clang][DebugInfo] Emit DW_AT_defaulted for defaulted C++ member functions

[Michael137]

Summary

This patch implements the DWARFv5 feature where a
DW_AT_defaulted is attached to DW_TAG_subprograms
which are explicitly defaulted in C++, i.e., member
functions such as the following:

class C {
  C() = default;
  ~C() = default;
};

We add two new spFlags, one for each possible value of
DW_AT_defaulted (see table in section 5.7.8 of DWARFv5
specification).

[Michael137]

• remove redundant includes

[Michael137]

• clang-format

[dblaikie]

Any particular use for this debug info in DWARF consumers?

[aprantl]

Not sure if this is the driving motivation, but this would probably allow LLDB's expression evaluator to synthesize a default implementation for these functions if they were optimized away.

clang/test/CodeGenCXX/debug-info-defaulted.cpp

31

typo: defaulted

clang/lib/CodeGen/CGDebugInfo.cpp

if (CGM.getTarget().getCXXABI().isItaniumFamily()) {
                            .getQuantity();
     }
     ContainingType = RecordTy;
   }
 
   if (Method->getCanonicalDecl()->isDeleted())
     SPFlags |= llvm::DISubprogram::SPFlagDeleted;
 
+  // The defaulted-ness of an out-of-class method is a property of its
+  // definition. Hence, query the definition instead.
+  if (auto const *Def = Method->getDefinition())
+    if (Def->isExplicitlyDefaulted())
+      SPFlags |= (Def->isOutOfLine())
+                     ? llvm::DISubprogram::SPFlagDefaultedOutOfClass
+                     : llvm::DISubprogram::SPFlagDefaultedInClass;
+
   if (Method->isNoReturn())
     Flags |= llvm::DINode::FlagNoReturn;
 
   if (Method->isStatic())
     Flags |= llvm::DINode::FlagStaticMember;
   if (Method->isImplicit())
     Flags |= llvm::DINode::FlagArtificial;
   Flags |= getAccessFlag(Method->getAccess(), Method->getParent());

clang/test/CodeGenCXX/debug-info-defaulted.cpp

+// Test for debug info for C++ defaulted member functions
+
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-linux-gnu %s -o - \
+// RUN:   -O0 -debug-info-kind=standalone -std=c++20 | FileCheck %s
+
+// CHECK:     DISubprogram(name: "defaulted", {{.*}}, flags: DIFlagPrototyped, spFlags: DISPFlagDefaultedInClass)
+// CHECK:     DISubprogram(name: "~defaulted", {{.*}}, flags: DIFlagPrototyped, spFlags: DISPFlagDefaultedOutOfClass)
+// CHECK:     DISubprogram(name: "operator=", {{.*}}, flags: DIFlagPrototyped, spFlags: 0)
+// CHECK:     DISubprogram(name: "operator=", {{.*}}, flags: DIFlagPrototyped, spFlags: 0)
+// CHECK:     DISubprogram(name: "operator==", {{.*}}, flags: DIFlagPrototyped, spFlags: DISPFlagDefaultedInClass)
+// CHECK-NOT: DISubprogram(name: "implicit_defaulted"
+struct defaulted {
+  // inline defaulted
+  defaulted() = default;
+
+  // out-of-line defaulted (inline keyword
+  // shouldn't change that)
+  inline ~defaulted();
+
+  // These shouldn't produce a defaulted-ness DI flag
+  // (though technically they are DW_DEFAULTED_no)
+  defaulted& operator=(defaulted const&) { return *this; }
+  defaulted& operator=(defaulted &&);
+
+  bool operator==(defaulted const&) const = default;
+};
+
+defaulted::~defaulted() = default;
+defaulted& defaulted::operator=(defaulted &&) { return *this; }
+
+// All ctors/dtors are implicitly defatuled.
+// So no DW_AT_defaulted expected for these.
+struct implicit_defaulted {};
+
+void foo() {
+  defaulted d;
+  implicit_defaulted i;
+}