[TableGen] Use std::move instead of swap. NFC. (#81606)

Historically TableGen has used `A.swap(B)` to move containers without
the expense of copying them. Perhaps this predated rvalue references. In
any case `A = std::move(B)` seems like a more direct way to implement
this when only A is required after the operation.

Author: jayfoad

llvm/utils/TableGen/AsmMatcherEmitter.cpp

@@ -1269,11 +1269,10 @@ void AsmMatcherInfo::buildRegisterClasses(
       }
 
       RegisterSet Tmp;
-      std::swap(Tmp, ContainingSet);
-      std::insert_iterator<RegisterSet> II(ContainingSet,
-                                           ContainingSet.begin());
-      std::set_intersection(Tmp.begin(), Tmp.end(), RS.begin(), RS.end(), II,
-                            LessRecordByID());
+      std::insert_iterator<RegisterSet> II(Tmp, Tmp.begin());
+      std::set_intersection(ContainingSet.begin(), ContainingSet.end(),
+                            RS.begin(), RS.end(), II, LessRecordByID());
+      ContainingSet = std::move(Tmp);
     }
 
     if (!ContainingSet.empty()) {

llvm/utils/TableGen/CodeGenRegisters.cpp

@@ -1964,9 +1964,9 @@ void CodeGenRegBank::pruneUnitSets() {
   for (unsigned i = 0, e = SuperSetIDs.size(); i != e; ++i) {
     unsigned SuperIdx = SuperSetIDs[i];
     PrunedUnitSets[i].Name = RegUnitSets[SuperIdx].Name;
-    PrunedUnitSets[i].Units.swap(RegUnitSets[SuperIdx].Units);
+    PrunedUnitSets[i].Units = std::move(RegUnitSets[SuperIdx].Units);
   }
-  RegUnitSets.swap(PrunedUnitSets);
+  RegUnitSets = std::move(PrunedUnitSets);
 }
 
 // Create a RegUnitSet for each RegClass that contains all units in the class
@@ -2139,7 +2139,7 @@ void CodeGenRegBank::computeRegUnitSets() {
     if (RCUnitSetsIdx == RegClassUnitSets.size()) {
       // Create a new list of UnitSets as a "fake" register class.
       RegClassUnitSets.resize(RCUnitSetsIdx + 1);
-      RegClassUnitSets[RCUnitSetsIdx].swap(RUSets);
+      RegClassUnitSets[RCUnitSetsIdx] = std::move(RUSets);
     }
   }
 }

llvm/utils/TableGen/CodeGenSchedule.cpp

@@ -1788,7 +1788,7 @@ void CodeGenSchedModels::inferFromRW(ArrayRef<unsigned> OperWrites,
     for (const PredTransition &Trans : LastTransitions)
       SubstitutedAny |= Transitions.substituteVariants(Trans);
     LLVM_DEBUG(Transitions.dump());
-    LastTransitions.swap(Transitions.TransVec);
+    LastTransitions = std::move(Transitions.TransVec);
   } while (SubstitutedAny);
 
   // WARNING: We are about to mutate the SchedClasses vector. Do not refer to

llvm/utils/TableGen/GlobalISelMatchTable.cpp

@@ -545,8 +545,8 @@ void GroupMatcher::optimize() {
     if (T != E)
       F = ++T;
   }
-  optimizeRules<GroupMatcher>(Matchers, MatcherStorage).swap(Matchers);
-  optimizeRules<SwitchMatcher>(Matchers, MatcherStorage).swap(Matchers);
+  Matchers = optimizeRules<GroupMatcher>(Matchers, MatcherStorage);
+  Matchers = optimizeRules<SwitchMatcher>(Matchers, MatcherStorage);
 }
 
 //===- SwitchMatcher ------------------------------------------------------===//

llvm/utils/TableGen/SubtargetEmitter.cpp

@@ -1649,7 +1649,7 @@ static void collectProcessorIndices(const CodeGenSchedClass &SC,
     IdxVec PI;
     std::set_union(&T.ProcIndex, &T.ProcIndex + 1, ProcIndices.begin(),
                    ProcIndices.end(), std::back_inserter(PI));
-    ProcIndices.swap(PI);
+    ProcIndices = std::move(PI);
   }
 }