[TableGen] Avoid unnecessary std::string creations

[RKSimon]

Summary

Avoid unnecessary std::string creations in the TreePredicateFn getters and in CodeGenDAGPatterns::getSDNodeNamed

utils/TableGen/CodeGenDAGPatterns.h

public:
   /// isAlwaysTrue - Return true if this is a noop predicate.
   bool isAlwaysTrue() const;
 
   bool isImmediatePattern() const { return !getImmCode().empty(); }
 
   /// getImmediatePredicateCode - Return the code that evaluates this pattern if
   /// this is an immediate predicate.  It is an error to call this on a
   /// non-immediate pattern.
-  std::string getImmediatePredicateCode() const {
-    std::string Result = getImmCode();
+  StringRef getImmediatePredicateCode() const {
+    StringRef Result = getImmCode();
     assert(!Result.empty() && "Isn't an immediate pattern!");
     return Result;
   }
 
 
   bool operator==(const TreePredicateFn &RHS) const {
     return PatFragRec == RHS.PatFragRec;
   }
 
   bool operator!=(const TreePredicateFn &RHS) const { return !(*this == RHS); }
 
   /// Return the name to use in the generated code to reference this, this is
   /// "Predicate_foo" if from a pattern fragment "foo".
   std::string getFnName() const;
 
   /// getCodeToRunOnSDNode - Return the code for the function body that
   /// evaluates this predicate.  The argument is expected to be in "Node",
   /// not N.  This handles casting and conversion to a concrete node type as
   /// appropriate.
   std::string getCodeToRunOnSDNode() const;
 
 private:
-  std::string getPredCode() const;
-  std::string getImmCode() const;
+  StringRef getPredCode() const;
+  StringRef getImmCode() const;
 };
 
 
 /// FIXME: TreePatternNode's can be shared in some cases (due to dag-shaped
 /// patterns), and as such should be ref counted.  We currently just leak all
 /// TreePatternNode objects!
 class TreePatternNode {
   /// The type of each node result.  Before and during type inference, each

 
 public:
   CodeGenDAGPatterns(RecordKeeper &R);
 
   CodeGenTarget &getTargetInfo() { return Target; }
   const CodeGenTarget &getTargetInfo() const { return Target; }
   const TypeSetByHwMode &getLegalTypes() const { return LegalVTS; }
 
-  Record *getSDNodeNamed(const std::string &Name) const;
+  Record *getSDNodeNamed(StringRef Name) const;
 
   const SDNodeInfo &getSDNodeInfo(Record *R) const {
     assert(SDNodes.count(R) && "Unknown node!");
     return SDNodes.find(R)->second;
   }
 
   // Node transformation lookups.
   typedef std::pair<Record*, std::string> NodeXForm;

utils/TableGen/CodeGenDAGPatterns.cpp

 //===----------------------------------------------------------------------===//
 
 /// TreePredicateFn constructor.  Here 'N' is a subclass of PatFrag.
 TreePredicateFn::TreePredicateFn(TreePattern *N) : PatFragRec(N) {
   assert((getPredCode().empty() || getImmCode().empty()) &&
         ".td file corrupt: can't have a node predicate *and* an imm predicate");
 }
 
-std::string TreePredicateFn::getPredCode() const {
+StringRef TreePredicateFn::getPredCode() const {
   return PatFragRec->getRecord()->getValueAsString("PredicateCode");
 }
 
-std::string TreePredicateFn::getImmCode() const {
+StringRef TreePredicateFn::getImmCode() const {
   return PatFragRec->getRecord()->getValueAsString("ImmediateCode");
 }
 
 
 /// isAlwaysTrue - Return true if this is a noop predicate.
 bool TreePredicateFn::isAlwaysTrue() const {
   return getPredCode().empty() && getImmCode().empty();
 }
 
 /// Return the name to use in the generated code to reference this, this is
 /// "Predicate_foo" if from a pattern fragment "foo".
 std::string TreePredicateFn::getFnName() const {
   return "Predicate_" + PatFragRec->getRecord()->getName().str();
 }
 
 /// getCodeToRunOnSDNode - Return the code for the function body that
 /// evaluates this predicate.  The argument is expected to be in "Node",
 /// not N.  This handles casting and conversion to a concrete node type as
 /// appropriate.
 std::string TreePredicateFn::getCodeToRunOnSDNode() const {
   // Handle immediate predicates first.
-  std::string ImmCode = getImmCode();
+  StringRef ImmCode = getImmCode();
   if (!ImmCode.empty()) {
     std::string Result =
       "    int64_t Imm = cast<ConstantSDNode>(Node)->getSExtValue();\n";
-    return Result + ImmCode;
+    return Result + ImmCode.str();
   }
 
   // Handle arbitrary node predicates.
   assert(!getPredCode().empty() && "Don't have any predicate code!");
-  std::string ClassName;
+  StringRef ClassName;
   if (PatFragRec->getOnlyTree()->isLeaf())
     ClassName = "SDNode";
   else {
     Record *Op = PatFragRec->getOnlyTree()->getOperator();
     ClassName = PatFragRec->getDAGPatterns().getSDNodeInfo(Op).getSDClassName();
   }
   std::string Result;
   if (ClassName == "SDNode")
     Result = "    SDNode *N = Node;\n";
   else
-    Result = "    auto *N = cast<" + ClassName + ">(Node);\n";
+    Result = "    auto *N = cast<" + ClassName.str() + ">(Node);\n";
 
-  return Result + getPredCode();
+  return Result + getPredCode().str();
 }
 
 //===----------------------------------------------------------------------===//
 // PatternToMatch implementation
 //
 
 /// getPatternSize - Return the 'size' of this pattern.  We want to match large
 /// patterns before small ones.  This is used to determine the size of a
CodeGenDAGPatterns::CodeGenDAGPatterns(RecordKeeper &R) :
   // stores, and side effects in many cases by examining an
   // instruction's pattern.
   InferInstructionFlags();
 
   // Verify that instruction flags match the patterns.
   VerifyInstructionFlags();
 }
 
-Record *CodeGenDAGPatterns::getSDNodeNamed(const std::string &Name) const {
+Record *CodeGenDAGPatterns::getSDNodeNamed(StringRef Name) const {
   Record *N = Records.getDef(Name);
   if (!N || !N->isSubClassOf("SDNode"))
     PrintFatalError("Error getting SDNode '" + Name + "'!");
 
   return N;
 }
 
 // Parse all of the SDNode definitions for the target, populating SDNodes.