[PATCH] D45438: [CodeView] Enable debugging of captured variables within C++ lambdas

[Brock Wyma via Phabricator via llvm-commits]

bwyma created this revision.
bwyma added reviewers: rnk, zturner, smerritt.
Herald added subscribers: JDevlieghere, aprantl.

When emitting CodeView debug information, C++ lambda types need a unique identifier so Visual Studio can match the forward reference for the type to the definition.  Currently they are all named "<unnamed-tag>".  This patch, combined with https://reviews.llvm.org/D32498, will enable debugging of captured variables within lambdas using Visual Studio.

Previous LF_CLASS type record for a lambda looks like this:

  Class (0x100A) {
    TypeLeafKind: LF_CLASS (0x1504)
    ...
    Name: main::<unnamed-tag>
  }

After this change the type record looks like this:

  Class (0x100A) {
    TypeLeafKind: LF_CLASS (0x1504)
    ...
    Name: main::<unnamed-tag>
    LinkageName: .?AV<lambda_0>@?0??main@@9@
  }

Manufacturing a better "name" for the lambda object is not necessary to allow proper debugging of captured variables.


https://reviews.llvm.org/D45438

Files:
  llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
  llvm/tools/clang/test/CodeGenCXX/debug-info-lamda.cpp


Index: llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
+++ llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -799,15 +799,21 @@
   }
 }
 
+static bool isCodeViewCXXLambda(const TagDecl *TD, CodeGenModule& CGM) {
+  const auto *CXXDecl = dyn_cast<CXXRecordDecl>(TD);
+  return CGM.getCodeGenOpts().EmitCodeView && CXXDecl && CXXDecl->isLambda();
+}
+
 /// In C++ mode, types have linkage, so we can rely on the ODR and
-/// on their mangled names, if they're external.
+/// on their mangled names, if they're external or a CodeView C++ Lambda.
 static SmallString<256> getUniqueTagTypeName(const TagType *Ty,
                                              CodeGenModule &CGM,
                                              llvm::DICompileUnit *TheCU) {
   SmallString<256> FullName;
   const TagDecl *TD = Ty->getDecl();
 
-  if (!hasCXXMangling(TD, TheCU) || !TD->isExternallyVisible())
+  if (!hasCXXMangling(TD, TheCU) || 
+      (!TD->isExternallyVisible() && !isCodeViewCXXLambda(TD, CGM)))
     return FullName;
 
   // TODO: This is using the RTTI name. Is there a better way to get
Index: llvm/tools/clang/test/CodeGenCXX/debug-info-lamda.cpp
===================================================================
--- llvm/tools/clang/test/CodeGenCXX/debug-info-lamda.cpp
+++ llvm/tools/clang/test/CodeGenCXX/debug-info-lamda.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -debug-info-kind=limited -S -emit-llvm -std=c++11 -o - %s | FileCheck --check-prefix LINUX %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -debug-info-kind=limited -gcodeview -S -emit-llvm -std=c++11 -o - %s | FileCheck --check-prefix MSVC %s
+
+int main(int argc, char* argv[], char* arge[]) {
+  auto lambda = [argc](int count) -> int { return argc == count ? 1 : 0; };
+  return lambda(0);
+}
+
+// LINUX: !DICompositeType(tag: DW_TAG_class_type
+// LINUX-NOT: name:
+// LINUX-NOT: identifier:
+// LINUX-SAME: )
+//
+// MSVC: define{{.*}} i32 @"??R<lambda_0>@?0??main@@9 at QEBA@H at Z"
+// MSVC: !DICompositeType(tag: DW_TAG_class_type
+// MSVC-NOT: name:
+// MSVC-SAME: identifier: ".?AV<lambda_0>@?0??main@@9@"
+// MSVC-SAME: )


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