[DebugInfo] Emit DW_TAG_enumeration_type for referenced global enumerator.

[ychen]

Summary

This essentially reverts changes from r361400.

[akhuang]

What is the reason for this change? The test case and comment changes don't seem related to the actual code change, which would affect DIGlobalVariables.

[rnk]

clang/lib/CodeGen/CGDebugInfo.cpp

4441–4462

Please simplify the logic and make these comments more coherent and understandable. This return is redundant with the later return, for example.

Basically, rC361400 removed an otherwise unused call to getOrCreateType. getOrCreateType happens to have the side effect of recording all enum types on the side in DIBuilder::AllEnumTypes, which are eventually referred to by the compile unit.

[ychen]

• address comment

[rnk]

lgtm, thanks!

[ychen]

In D67141#1658238, @rnk wrote:

lgtm, thanks!

Thank you!

clang/lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::EmitGlobalVariable(const ValueDecl *VD, const APValue &Init) {
   if (VD->hasAttr<NoDebugAttr>())
     return;
   auto Align = getDeclAlignIfRequired(VD, CGM.getContext());
   // Create the descriptor for the variable.
   llvm::DIFile *Unit = getOrCreateFile(VD->getLocation());
   StringRef Name = VD->getName();
   llvm::DIType *Ty = getOrCreateType(VD->getType(), Unit);
 
-  // Do not use global variables for enums, unless in CodeView.
+  // Use global variables for enums in CodeView, use DW_TAG_enumeration_type for
+  // enums for non-CodeView.
   if (const auto *ECD = dyn_cast<EnumConstantDecl>(VD)) {
     const auto *ED = cast<EnumDecl>(ECD->getDeclContext());
     assert(isa<EnumType>(ED->getTypeForDecl()) && "Enum without EnumType?");
-    (void)ED;
+
+    // If not CodeView, emit DW_TAG_enumeration_type if necessary.
+    if (!CGM.getCodeGenOpts().EmitCodeView) {
+      llvm::DIType *EDTy =
+          getOrCreateType(QualType(ED->getTypeForDecl(), 0), Unit);
+      if (EDTy->getTag() == llvm::dwarf::DW_TAG_enumeration_type)
+        return;
+    }
 
     // If CodeView, emit enums as global variables, unless they are defined
     // inside a class. We do this because MSVC doesn't emit S_CONSTANTs for
     // enums in classes, and because it is difficult to attach this scope
     // information to the global variable.
     if (!CGM.getCodeGenOpts().EmitCodeView ||
         isa<RecordDecl>(ED->getDeclContext()))
       return;
   }
 
   llvm::DIScope *DContext = nullptr;
 
   // Do not emit separate definitions for function local consts.
   if (isa<FunctionDecl>(VD->getDeclContext()))
     return;
 
   // Emit definition for static members in CodeView.

clang/test/CodeGen/enum2.c

-// RUN: %clang_cc1 -triple i386-unknown-unknown %s -debug-info-kind=limited -emit-llvm -o /dev/null
+// RUN: %clang_cc1 -triple i386-unknown-unknown %s -debug-info-kind=limited -emit-llvm -o - | FileCheck %s
+
 int v;
 enum e { MAX };
 
 void foo (void)
 {
   v = MAX;
 }
+// CHECK: !DICompositeType(tag: DW_TAG_enumeration_type,
+// CHECK-SAME: baseType: ![[LONG:[0-9]+]]
+// CHECK-SAME: elements: ![[ELTS:[0-9]+]]
+// CHECK: ![[LONG]] = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+// CHECK: ![[ELTS]] = !{![[MAX:[0-9]+]]}
+// CHECK: ![[MAX]] = !DIEnumerator(name: "MAX", value: 0, isUnsigned: true)