[WebAssembly][MC] Use StringRef over std::string pointer

This is followup based on feedback on 5be42f3.
See: https://reviews.llvm.org/D77627.

Differential Revision: https://reviews.llvm.org/D77674

Author: sbc100

llvm/include/llvm/MC/MCSymbolWasm.h

@@ -19,15 +19,13 @@ class MCSymbolWasm : public MCSymbol {
   bool IsHidden = false;
   bool IsComdat = false;
   mutable bool IsUsedInGOT = false;
+  Optional<StringRef> ImportModule;
+  Optional<StringRef> ImportName;
+  Optional<StringRef> ExportName;
+  wasm::WasmSignature *Signature = nullptr;
   Optional<wasm::WasmGlobalType> GlobalType;
   Optional<wasm::WasmEventType> EventType;
 
-  // Non-owning pointers since MCSymbol must be trivially destructible.
-  std::string *ImportModule = nullptr;
-  std::string *ImportName = nullptr;
-  std::string *ExportName = nullptr;
-  wasm::WasmSignature *Signature = nullptr;
-
   /// An expression describing how to calculate the size of a symbol. If a
   /// symbol has no size this field will be NULL.
   const MCExpr *SymbolSize = nullptr;
@@ -71,32 +69,29 @@ class MCSymbolWasm : public MCSymbol {
   bool isComdat() const { return IsComdat; }
   void setComdat(bool isComdat) { IsComdat = isComdat; }
 
-  bool hasImportModule() const { return ImportModule != nullptr; }
+  bool hasImportModule() const { return ImportModule.hasValue(); }
   StringRef getImportModule() const {
-    if (ImportModule)
-      return StringRef(*ImportModule);
+    if (ImportModule.hasValue())
+      return ImportModule.getValue();
     // Use a default module name of "env" for now, for compatibility with
     // existing tools.
     // TODO(sbc): Find a way to specify a default value in the object format
     // without picking a hardcoded value like this.
     return "env";
   }
-  void setImportModule(std::string *Name) { ImportModule = Name; }
+  void setImportModule(StringRef Name) { ImportModule = Name; }
 
-  bool hasImportName() const { return ImportName != nullptr; }
+  bool hasImportName() const { return ImportName.hasValue(); }
   StringRef getImportName() const {
-    if (ImportName)
-      return StringRef(*ImportName);
+    if (ImportName.hasValue())
+      return ImportName.getValue();
     return getName();
   }
-  void setImportName(std::string *Name) { ImportName = Name; }
+  void setImportName(StringRef Name) { ImportName = Name; }
 
-  bool hasExportName() const { return ExportName != nullptr; }
-  StringRef getExportName() const {
-    assert(ExportName);
-    return StringRef(*ExportName);
-  }
-  void setExportName(std::string *Name) { ExportName = Name; }
+  bool hasExportName() const { return ExportName.hasValue(); }
+  StringRef getExportName() const { return ExportName.getValue(); }
+  void setExportName(StringRef Name) { ExportName = Name; }
 
   void setUsedInGOT() const { IsUsedInGOT = true; }
   bool isUsedInGOT() const { return IsUsedInGOT; }

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

@@ -233,10 +233,10 @@ class WebAssemblyAsmParser final : public MCTargetAsmParser {
     Signatures.push_back(std::move(Sig));
   }
 
-  std::string *storeName(StringRef Name) {
+  StringRef storeName(StringRef Name) {
     std::unique_ptr<std::string> N = std::make_unique<std::string>(Name);
     Names.push_back(std::move(N));
-    return Names.back().get();
+    return *Names.back();
   }
 
   std::pair<StringRef, StringRef> nestingString(NestingType NT) {

llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.h

@@ -28,10 +28,10 @@ class LLVM_LIBRARY_VISIBILITY WebAssemblyAsmPrinter final : public AsmPrinter {
   std::vector<std::unique_ptr<wasm::WasmSignature>> Signatures;
   std::vector<std::unique_ptr<std::string>> Names;
 
-  std::string *storeName(StringRef Name) {
+  StringRef storeName(StringRef Name) {
     std::unique_ptr<std::string> N = std::make_unique<std::string>(Name);
     Names.push_back(std::move(N));
-    return Names.back().get();
+    return *Names.back();
   }
 
 public: