Reland "[clang][DebugInfo][NFC] Simplify CollectRecordLambdaFields"

This reverts commit 99a29f6.

Original change was reverted because following assertion started firing:
```
clang++: clang/include/clang/AST/LambdaCapture.h:105: ValueDecl
*clang::LambdaCapture::getCapturedVar() const: Assertion
`capturesVariable() && "No variable available for capture"' failed.

PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.

Stack dump:
0.Program arguments: ../../prebuilt/third_party/clang/custom/bin/clang++ -MD -MF host_x64/obj/third_party/android/platform/system/libbase/libbase.logging.cpp.o.d -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -I../.. -Ihost_x64/gen -I../../third_party/android/platform/system/libbase/include -I../../third_party/fmtlib/src/include -I../../third_party/android/platfo...com
1.<eof> parser at end of file
2.Per-file LLVM IR generation
clang++: error: clang frontend command failed with exit code 134 (use -v
to see invocation)
Fuchsia clang version 22.0.0git
(https://llvm.googlesource.com/llvm-project
8553bd2)
********************
```

The relanded patch just adds a `Capture.capturesVariable()` check before calling `getCapturedVar`. That's what the code did before the refactor.

Author: Michael137

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -26,6 +26,7 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
+#include "clang/AST/LambdaCapture.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/VTableBuilder.h"
@@ -1903,46 +1904,61 @@ CGDebugInfo::createInlinedSubprogram(StringRef FuncName,
   return SP;
 }
 
+llvm::StringRef
+CGDebugInfo::GetLambdaCaptureName(const LambdaCapture &Capture) {
+  if (Capture.capturesThis())
+    return CGM.getCodeGenOpts().EmitCodeView ? "__this" : "this";
+
+  assert(Capture.capturesVariable());
+
+  const ValueDecl *CaptureDecl = Capture.getCapturedVar();
+  assert(CaptureDecl && "Expected valid decl for captured variable.");
+
+  return CaptureDecl->getName();
+}
+
 void CGDebugInfo::CollectRecordLambdaFields(
     const CXXRecordDecl *CXXDecl, SmallVectorImpl<llvm::Metadata *> &elements,
     llvm::DIType *RecordTy) {
   // For C++11 Lambdas a Field will be the same as a Capture, but the Capture
   // has the name and the location of the variable so we should iterate over
   // both concurrently.
-  const ASTRecordLayout &layout = CGM.getContext().getASTRecordLayout(CXXDecl);
   RecordDecl::field_iterator Field = CXXDecl->field_begin();
   unsigned fieldno = 0;
   for (CXXRecordDecl::capture_const_iterator I = CXXDecl->captures_begin(),
                                              E = CXXDecl->captures_end();
        I != E; ++I, ++Field, ++fieldno) {
-    const LambdaCapture &C = *I;
-    if (C.capturesVariable()) {
-      SourceLocation Loc = C.getLocation();
-      assert(!Field->isBitField() && "lambdas don't have bitfield members!");
-      ValueDecl *V = C.getCapturedVar();
-      StringRef VName = V->getName();
-      llvm::DIFile *VUnit = getOrCreateFile(Loc);
-      auto Align = getDeclAlignIfRequired(V, CGM.getContext());
-      llvm::DIType *FieldType = createFieldType(
-          VName, Field->getType(), Loc, Field->getAccess(),
-          layout.getFieldOffset(fieldno), Align, VUnit, RecordTy, CXXDecl);
-      elements.push_back(FieldType);
-    } else if (C.capturesThis()) {
+    const LambdaCapture &Capture = *I;
+    const uint64_t FieldOffset =
+        CGM.getContext().getASTRecordLayout(CXXDecl).getFieldOffset(fieldno);
+
+    assert(!Field->isBitField() && "lambdas don't have bitfield members!");
+
+    SourceLocation Loc;
+    uint32_t Align = 0;
+
+    if (Capture.capturesThis()) {
       // TODO: Need to handle 'this' in some way by probably renaming the
       // this of the lambda class and having a field member of 'this' or
       // by using AT_object_pointer for the function and having that be
       // used as 'this' for semantic references.
-      FieldDecl *f = *Field;
-      llvm::DIFile *VUnit = getOrCreateFile(f->getLocation());
-      QualType type = f->getType();
-      StringRef ThisName =
-          CGM.getCodeGenOpts().EmitCodeView ? "__this" : "this";
-      llvm::DIType *fieldType = createFieldType(
-          ThisName, type, f->getLocation(), f->getAccess(),
-          layout.getFieldOffset(fieldno), VUnit, RecordTy, CXXDecl);
-
-      elements.push_back(fieldType);
+      Loc = Field->getLocation();
+    } else if (Capture.capturesVariable()) {
+      Loc = Capture.getLocation();
+
+      const ValueDecl *CaptureDecl = Capture.getCapturedVar();
+      assert(CaptureDecl && "Expected valid decl for captured variable.");
+
+      Align = getDeclAlignIfRequired(CaptureDecl, CGM.getContext());
+    } else {
+      continue;
     }
+
+    llvm::DIFile *VUnit = getOrCreateFile(Loc);
+
+    elements.push_back(createFieldType(
+        GetLambdaCaptureName(Capture), Field->getType(), Loc,
+        Field->getAccess(), FieldOffset, Align, VUnit, RecordTy, CXXDecl));
   }
 }
 

clang/lib/CodeGen/CGDebugInfo.h

@@ -397,6 +397,7 @@ class CGDebugInfo {
   void CollectRecordFields(const RecordDecl *Decl, llvm::DIFile *F,
                            SmallVectorImpl<llvm::Metadata *> &E,
                            llvm::DICompositeType *RecordTy);
+  llvm::StringRef GetLambdaCaptureName(const LambdaCapture &Capture);
 
   /// If the C++ class has vtable info then insert appropriate debug
   /// info entry in EltTys vector.