[TableGen] Remove some copies around PatternToMatch.

[craig.topper]

Summary

This patch does a few things that should remove some copies around PatternsToMatch. These were noticed while reviewing code for D34341.

Change constructor to take Dstregs by value and move it into the class. Change one of the callers to add std::move to the argument so that it gets moved.

Make AddPatternToMatch take PatternToMatch by rvalue reference so we can move it into the PatternsToMatch vector. I believe we should have a implicit default move constructor available on PatternToMatch. I chose rvalue reference because both callers call it with temporaries already.

[aymanmus]

This mainly solves the problem described in D34341, only thing left is to change the call of emplace_back([argumetns]) with push_back(PatternToMatch([arguments])).
I'll update my patch and mark it as dependent with this one.

In the case of the PatternToMatch class (which includes only pointers, integers and a vector), I believe the move constructor would be implicitly declared by the compiler, and as the temp object passed to push_back is an rvalue, the implicit move constructor would be called.

utils/TableGen/CodeGenDAGPatterns.h

public:
 
   TreePatternNode *getResultPattern() const { return ResultPattern; }
 };
 
 /// PatternToMatch - Used by CodeGenDAGPatterns to keep tab of patterns
 /// processed to produce isel.
 class PatternToMatch {
 public:
-  PatternToMatch(Record *srcrecord, ListInit *preds,
-                 TreePatternNode *src, TreePatternNode *dst,
-                 const std::vector<Record*> &dstregs,
+  PatternToMatch(Record *srcrecord, ListInit *preds, TreePatternNode *src,
+                 TreePatternNode *dst, std::vector<Record *> dstregs,
                  int complexity, unsigned uid)
-    : SrcRecord(srcrecord), Predicates(preds), SrcPattern(src), DstPattern(dst),
-      Dstregs(dstregs), AddedComplexity(complexity), ID(uid) {}
+      : SrcRecord(srcrecord), Predicates(preds), SrcPattern(src),
+        DstPattern(dst), Dstregs(std::move(dstregs)),
+        AddedComplexity(complexity), ID(uid) {}
 
   Record          *SrcRecord;   // Originating Record for the pattern.
   ListInit        *Predicates;  // Top level predicate conditions to match.
   TreePatternNode *SrcPattern;  // Source pattern to match.
   TreePatternNode *DstPattern;  // Resulting pattern.
   std::vector<Record*> Dstregs; // Physical register defs being matched.
   int              AddedComplexity; // Add to matching pattern complexity.
   unsigned         ID;          // Unique ID for the record.
private:
   void ParsePatternFragments(bool OutFrags = false);
   void ParseDefaultOperands();
   void ParseInstructions();
   void ParsePatterns();
   void InferInstructionFlags();
   void GenerateVariants();
   void VerifyInstructionFlags();
 
-  void AddPatternToMatch(TreePattern *Pattern, const PatternToMatch &PTM);
+  void AddPatternToMatch(TreePattern *Pattern, PatternToMatch &&PTM);
   void FindPatternInputsAndOutputs(TreePattern *I, TreePatternNode *Pat,
                                    std::map<std::string,
                                    TreePatternNode*> &InstInputs,
                                    std::map<std::string,
                                    TreePatternNode*> &InstResults,
                                    std::vector<Record*> &InstImpResults);
 };
 } // end namespace llvm
 
 #endif

utils/TableGen/CodeGenDAGPatterns.cpp

static void FindNames(const TreePatternNode *P,
 
   if (!P->isLeaf()) {
     for (unsigned i = 0, e = P->getNumChildren(); i != e; ++i)
       FindNames(P->getChild(i), Names, PatternTop);
   }
 }
 
 void CodeGenDAGPatterns::AddPatternToMatch(TreePattern *Pattern,
-                                           const PatternToMatch &PTM) {
+                                           PatternToMatch &&PTM) {
   // Do some sanity checking on the pattern we're about to match.
   std::string Reason;
   if (!PTM.getSrcPattern()->canPatternMatch(Reason, *this)) {
     PrintWarning(Pattern->getRecord()->getLoc(),
       Twine("Pattern can never match: ") + Reason);
     return;
   }
 
void CodeGenDAGPatterns::AddPatternToMatch(TreePattern *Pattern,
 
   // Scan all of the named values in the source pattern, rejecting them if the
   // name isn't used in the dest, and isn't used to tie two values together.
   for (const auto &Entry : SrcNames)
     if (DstNames[Entry.first].first == nullptr &&
         SrcNames[Entry.first].second == 1)
       Pattern->error("Pattern has dead named input: $" + Entry.first);
 
-  PatternsToMatch.push_back(PTM);
+  PatternsToMatch.push_back(std::move(PTM));
 }
 
 
 
 void CodeGenDAGPatterns::InferInstructionFlags() {
   ArrayRef<const CodeGenInstruction*> Instructions =
     Target.getInstructionsByEnumValue();
 
if (!DstPattern->isLeaf())
                                        DstPattern->getNumTypes());
 
     for (unsigned i = 0, e = Result.getOnlyTree()->getNumTypes(); i != e; ++i)
       DstPattern->setType(i, Result.getOnlyTree()->getExtType(i));
 
     TreePattern Temp(Result.getRecord(), DstPattern, false, *this);
     Temp.InferAllTypes();
 
-
-    AddPatternToMatch(Pattern,
-                    PatternToMatch(CurPattern,
-                                   CurPattern->getValueAsListInit("Predicates"),
-                                   Pattern->getTree(0),
-                                   Temp.getOnlyTree(), InstImpResults,
-                                   CurPattern->getValueAsInt("AddedComplexity"),
-                                   CurPattern->getID()));
+    AddPatternToMatch(
+        Pattern,
+        PatternToMatch(
+            CurPattern, CurPattern->getValueAsListInit("Predicates"),
+            Pattern->getTree(0), Temp.getOnlyTree(), std::move(InstImpResults),
+            CurPattern->getValueAsInt("AddedComplexity"), CurPattern->getID()));
   }
 }
 
 /// CombineChildVariants - Given a bunch of permutations of each child of the
 /// 'operator' node, put them together in all possible ways.
 static void CombineChildVariants(TreePatternNode *Orig,
                const std::vector<std::vector<TreePatternNode*> > &ChildVariants,
                                  std::vector<TreePatternNode*> &OutVariants,