[PATCH] D103131: support debug info for alias variable

[kamlesh kumar via Phabricator via cfe-commits]

kamleshbhalui created this revision.
kamleshbhalui added reviewers: dblaikie, aprantl, probinson.
kamleshbhalui added a project: LLVM.
Herald added a subscriber: jeroen.dobbelaere.
kamleshbhalui requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

consider below test demonstration
$cat test.c
int oldname = 1;
extern int newname __attribute__((alias("oldname")));

$clang -g -O0 test.c

$gdb a.out
(gdb) pt oldname
type = int
(gdb) pt newname
type = <data variable, no debug info>
(gdb) p newname
'newname' has unknown type; cast it to its declared type

debugger is unable to print newname types and value because clang does not emit debug info for newname.
This patch supports having debug info for alias variable as imported entity.

Fixes PR50052.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103131

Files:
  clang/lib/CodeGen/CGDebugInfo.cpp
  clang/lib/CodeGen/CGDebugInfo.h
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGen/debug-info-alias.c


Index: clang/test/CodeGen/debug-info-alias.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/debug-info-alias.c
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=limited -triple x86_64-linux-unknown %s -o - | FileCheck %s
+
+// CHECK: !DIImportedEntity(tag: DW_TAG_imported_declaration, scope:{{.*}}, entity: ![[VAR:[0-9]+]]
+// CHECK: ![[VAR]] = !DIGlobalVariable(name: "newname"
+
+int oldname = 1;
+extern int newname __attribute__((alias("oldname")));
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -4922,6 +4922,13 @@
       setTLSMode(GA, *VD);
 
   SetCommonAttributes(GD, GA);
+
+  // Emit global alias debug information.
+  if (const auto *VD = dyn_cast<VarDecl>(D)) {
+    if (CGDebugInfo *DI = getModuleDebugInfo())
+      if (getCodeGenOpts().hasReducedDebugInfo())
+        DI->EmitGlobalAlias(GA, VD);
+  }
 }
 
 void CodeGenModule::emitIFuncDefinition(GlobalDecl GD) {
Index: clang/lib/CodeGen/CGDebugInfo.h
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.h
+++ clang/lib/CodeGen/CGDebugInfo.h
@@ -493,6 +493,9 @@
   /// Emit information about an external variable.
   void EmitExternalVariable(llvm::GlobalVariable *GV, const VarDecl *Decl);
 
+  /// Emit information about global alias.
+  void EmitGlobalAlias(llvm::GlobalAlias *GA, const VarDecl *Decl);
+
   /// Emit C++ using directive.
   void EmitUsingDirective(const UsingDirectiveDecl &UD);
 
Index: clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.cpp
+++ clang/lib/CodeGen/CGDebugInfo.cpp
@@ -4945,6 +4945,19 @@
   Var->addDebugInfo(GVE);
 }
 
+void CGDebugInfo::EmitGlobalAlias(llvm::GlobalAlias *Var, const VarDecl *D) {
+  if (!CGM.getCodeGenOpts().hasReducedDebugInfo())
+    return;
+
+  llvm::DIFile *Unit = getOrCreateFile(D->getLocation());
+  llvm::DIScope *DContext = getDeclContextDescriptor(D);
+  if (llvm::DINode *Target = getDeclarationOrDefinition(D)) {
+    auto Loc = D->getLocation();
+    DBuilder.createImportedDeclaration(DContext, Target, Unit,
+                                       getLineNumber(Loc));
+  }
+}
+
 llvm::DIScope *CGDebugInfo::getCurrentContextDescriptor(const Decl *D) {
   if (!LexicalBlockStack.empty())
     return LexicalBlockStack.back();


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