[constant-folding] Eliminate complexity introducing pre-mature optimization.

The code that is deleted in this PR attempted to save a bit of compile time by:

1. Checking if after constant folding we have a tuple that is immediately tuple
   extracted from.
2. RAUW the tuple extracts directly from the tuple's operands.

This adds a bunch of complexity to the pass and also moves code that should be
in a visitor into the main pass workloop function.

After this PR what happens instead is that after we fold, we add the tuple to
the worklist. Then during the next iteration we look at the tuple_extract users
and simplify them at that point.

Author: gottesmm

lib/SILOptimizer/Utils/ConstantFolding.cpp

@@ -1939,51 +1939,8 @@ ConstantFolder::processWorkList() {
           // Ok, we have succeeded. Add user to the FoldedUsers list and perform
           // the necessary cleanups, RAUWs, etc.
           FoldedUsers.insert(User);
-          ++NumInstFolded;
-
           InvalidateInstructions = true;
-
-          // If the constant produced a tuple, be smarter than RAUW: explicitly
-          // nuke any tuple_extract instructions using the apply.  This is a
-          // common case for functions returning multiple values.
-          if (auto *TI = dyn_cast<TupleInst>(C)) {
-            for (SILValue Result : User->getResults()) {
-              for (auto UI = Result->use_begin(), UE = Result->use_end();
-                   UI != UE;) {
-                Operand *O = *UI++;
-
-                // If the user is a tuple_extract, just substitute the right
-                // value in.
-                if (auto *TEI = dyn_cast<TupleExtractInst>(O->getUser())) {
-                  SILValue NewVal = TI->getOperand(TEI->getFieldNo());
-                  TEI->replaceAllUsesWith(NewVal);
-                  TEI->dropAllReferences();
-                  FoldedUsers.insert(TEI);
-                  if (auto *Inst = NewVal->getDefiningInstruction())
-                    WorkList.insert(Inst);
-                  continue;
-                }
-
-                if (auto *DTI = dyn_cast<DestructureTupleInst>(O->getUser())) {
-                  SILValue NewVal = TI->getOperand(O->getOperandNumber());
-                  auto OwnershipKind = NewVal.getOwnershipKind();
-                  if (OwnershipKind.isCompatibleWith(
-                          ValueOwnershipKind::Guaranteed)) {
-                    SILValue DTIResult = DTI->getResult(O->getOperandNumber());
-                    DTIResult->replaceAllUsesWith(NewVal);
-                    FoldedUsers.insert(DTI);
-                    if (auto *Inst = NewVal->getDefiningInstruction())
-                      WorkList.insert(Inst);
-                    continue;
-                  }
-                }
-              }
-            }
-
-            if (llvm::all_of(User->getResults(),
-                             [](SILValue v) { return v->use_empty(); }))
-              FoldedUsers.insert(TI);
-          }
+          ++NumInstFolded;
 
           // We were able to fold, so all users should use the new folded
           // value. If we don't have any such users, continue.