[lldb] When matching entry values for async swift function, fallback to the current function from parent function when evaluating subexpressions.

This occurs when the parent function does not have debug info (*). In swift async
functions this is ok since we only need to be able to restore the ABI defined
context register for the async context (r14)... so it is not necessary to match
with a callsite parameter.

(*) E.x.: On Linux async funclets called from a libswift_Concurrency.so that had its
debug info stripped.

Author: gottesmm

lldb/source/Expression/DWARFExpression.cpp

@@ -731,13 +731,6 @@ static bool Evaluate_DW_OP_entry_value(std::vector<Value> &stack,
     return false;
   }
 
-  Function *parent_func =
-      parent_frame->GetSymbolContext(eSymbolContextFunction).function;
-  if (!parent_func) {
-    LLDB_LOG(log, "Evaluate_DW_OP_entry_value: no parent function");
-    return false;
-  }
-
   // 2. Find the call edge in the parent function responsible for creating the
   //    current activation.
   Function *current_func =
@@ -751,6 +744,7 @@ static bool Evaluate_DW_OP_entry_value(std::vector<Value> &stack,
   ModuleList &modlist = target.GetImages();
   ExecutionContext parent_exe_ctx = *exe_ctx;
   parent_exe_ctx.SetFrameSP(parent_frame);
+  Function *parent_func = nullptr;
 #ifdef LLDB_ENABLE_SWIFT
   // Swift async function arguments are represented relative to a
   // DW_OP_entry_value that fetches the async context register. This
@@ -760,6 +754,14 @@ static bool Evaluate_DW_OP_entry_value(std::vector<Value> &stack,
   auto fn_name = current_func->GetMangled().GetMangledName().GetStringRef();
   if (!SwiftLanguageRuntime::IsAnySwiftAsyncFunctionSymbol(fn_name)) {
 #endif
+
+  parent_func =
+    parent_frame->GetSymbolContext(eSymbolContextFunction).function;
+  if (!parent_func) {
+    LLDB_LOG(log, "Evaluate_DW_OP_entry_value: no parent function");
+    return false;
+  }
+
   if (!parent_frame->IsArtificial()) {
     // If the parent frame is not artificial, the current activation may be
     // produced by an ambiguous tail call. In this case, refuse to proceed.
@@ -845,7 +847,8 @@ static bool Evaluate_DW_OP_entry_value(std::vector<Value> &stack,
   }
   llvm::Optional<DWARFExpression> subexpr;
   if (!matched_param) {
-    subexpr.emplace(parent_func->CalculateSymbolContextModule(),
+    auto *ctx_func = parent_func ? parent_func : current_func;
+    subexpr.emplace(ctx_func->CalculateSymbolContextModule(),
                     DataExtractor(opcodes, subexpr_offset, subexpr_len),
                     dwarf_cu);
   }