From 1b5c2915a2318705727ada586290de15e2cad202 Mon Sep 17 00:00:00 2001
From: Amy Huang <akhuang@google.com>
Date: Fri, 5 Feb 2021 15:43:45 -0800
Subject: [PATCH] [DebugInfo] Add an attribute to force type info to be emitted
 for class types.

The goal is to provide a way to bypass constructor homing when emitting
class definitions and force class definitions in the debug info.

Not sure about the wording of the attribute, or whether it should be
specific to classes with constructors
---
 clang/include/clang/Basic/Attr.td             |  7 ++++++
 clang/lib/CodeGen/CGDebugInfo.cpp             |  4 ++++
 .../debug-info-emit-as-needed-attribute.cpp   | 22 +++++++++++++++++++
 3 files changed, 33 insertions(+)
 create mode 100644 clang/test/CodeGenCXX/debug-info-emit-as-needed-attribute.cpp

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index bc2d8ceeeb6c..5bddef1b4ef2 100644
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1660,6 +1660,13 @@ def NoDebug : InheritableAttr {
   let Documentation = [NoDebugDocs];
 }
 
+def DebugTypeInfoAsNeeded : InheritableAttr {
+  let Spellings = [Clang<"debug_type_info_as_needed">];
+  let Subjects = SubjectList<[CXXRecord]>;
+  let Documentation = [Undocumented];
+  let SimpleHandler = 1;
+}
+
 def NoDuplicate : InheritableAttr {
   let Spellings = [Clang<"noduplicate">];
   let Subjects = SubjectList<[Function]>;
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 48b9bf049f48..ef17983b446a 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -2344,6 +2344,10 @@ static bool shouldOmitDefinition(codegenoptions::DebugInfoKind DebugKind,
   if (!CXXDecl)
     return false;
 
+  // Don't omit definition if marked with attribute.
+  if (RD->hasAttr<DebugTypeInfoAsNeededAttr>())
+    return false;
+
   // Only emit complete debug info for a dynamic class when its vtable is
   // emitted.  However, Microsoft debuggers don't resolve type information
   // across DLL boundaries, so skip this optimization if the class or any of its
diff --git a/clang/test/CodeGenCXX/debug-info-emit-as-needed-attribute.cpp b/clang/test/CodeGenCXX/debug-info-emit-as-needed-attribute.cpp
new file mode 100644
index 000000000000..a2f0eae314c8
--- /dev/null
+++ b/clang/test/CodeGenCXX/debug-info-emit-as-needed-attribute.cpp
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -DSETATTR=0 -emit-llvm -std=c++14 -debug-info-kind=constructor %s -o - | FileCheck %s --check-prefix=DEBUG
+// RUN: %clang_cc1 -DSETATTR=1 -emit-llvm -std=c++14 -debug-info-kind=constructor %s -o - | FileCheck %s --check-prefix=WITHATTR
+
+#if SETATTR
+#define DEBUGASNEEDED __attribute__((debug_type_info_as_needed))
+#else
+#define DEBUGASNEEDED
+#endif
+
+// Struct that isn't constructed, so its full type info should be omitted with
+// -debug-info-kind=constructor.
+struct DEBUGASNEEDED some_struct {
+  some_struct() {}
+};
+
+void func1(some_struct s) {}
+// void func2() { func1(); }
+// DEBUG:  !DICompositeType({{.*}}name: "some_struct"
+// DEBUG-SAME:              flags: {{.*}}DIFlagFwdDecl
+// WITHATTR: !DICompositeType({{.*}}name: "some_struct"
+// WITHATTR-NOT: DIFlagFwdDecl
+