Comments, typos, and cleanup from review.

Author: atrick

include/swift/SIL/SILCloner.h

@@ -138,10 +138,16 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
            && "cloned instruction dropped debug scope");
   }
 
-  /// Visitor callback that maps an original value to an existing value. Called
-  /// whenever the visitor that clones an instruction skips doPostProcess().
+  /// Visitor callback that maps an original value to an existing value. If the
+  /// original instruction can be folded away in the cloned code, then the
+  /// instruction visitor should call this instead of cloning the instruction
+  /// and calling doPostProcess(). foldValue() and doPostProcess() are the only
+  /// two ways for a visitor to remap an original value that may be used within
+  /// the cloned region.
   void foldValue(SILValue origValue, SILValue mappedValue) {
-    ValueMap.insert({origValue, mappedValue});
+    auto iterAndInserted = ValueMap.insert({origValue, mappedValue});
+    (void)iterAndInserted;
+    assert(iterAndInserted.second && "Original value already mapped.");
   }
 
   /// Mark a block containing an unreachable instruction for use in the `fixUp`
@@ -316,7 +322,7 @@ class SILCloner : protected SILInstructionVisitor<ImplClass> {
   // terminator.
   void visitInstructionsInBlock(SILBasicBlock *BB);
 
-  // Visit a block's terminator. This is called with each block in DFS predorder
+  // Visit a block's terminator. This is called with each block in DFS preorder
   // after visiting and mapping all basic blocks and after visiting all
   // non-terminator instructions in the block.
   void visitTerminator(SILBasicBlock *BB) {
@@ -623,18 +629,14 @@ void SILCloner<ImplClass>::visitBlocksDepthFirst(
         continue;
 
       // Map the successor to a new BB.
-      auto *MappedBB = newF.createBasicBlock();
+      auto *MappedBB = insertBeforeBB
+        ? newF.createBasicBlockBefore(insertBeforeBB)
+        : newF.createBasicBlock();
+
       BBMap.insert(std::make_pair(Succ.getBB(), MappedBB));
 
       clonePhiArgs(Succ);
 
-      // Also, move the new mapped BB to the right position in the caller
-      if (insertBeforeBB) {
-        newF.getBlocks().splice(SILFunction::iterator(insertBeforeBB),
-                                newF.getBlocks(),
-                                SILFunction::iterator(MappedBB));
-      }
-
       dfsWorklist.push_back(Succ);
     }
     // Reverse the worklist to pop the successors in forward order.

include/swift/SILOptimizer/Utils/Local.h

@@ -377,7 +377,7 @@ class EdgeThreadingCloner : public BaseThreadingCloner {
           DestPHIArg->getType(), DestPHIArg->getOwnershipKind());
       // Since we don't call any CFG cloning entry point, we can call
       // `foldValue` immediately as if cloning has already started. This simply
-      // avoids handling AvailVals during `remap` or defining a custome
+      // avoids handling AvailVals during `remap` or defining a custom
       // visitSILPhiArgument().
       foldValue(DestPHIArg, BlockArg);
       AvailVals.push_back(std::make_pair(DestPHIArg, BlockArg));
@@ -427,7 +427,7 @@ class BasicBlockCloner : public BaseThreadingCloner {
       for (unsigned i = 0, e = FromBB->args_size(); i != e; ++i) {
         // Since we don't call any CFG cloning entry point, we can call
         // `foldValue` immediately as if cloning has already started. This
-        // simply avoids handling AvailVals during `remap` or defining a custome
+        // simply avoids handling AvailVals during `remap` or defining a custom
         // visitSILPhiArgument().
         foldValue(FromBB->getArgument(i), DestBB->getArgument(i));
         AvailVals.push_back(

include/swift/SILOptimizer/Utils/SILInliner.h

@@ -83,7 +83,7 @@ class SILInliner {
   ///
   /// *NOTE*: This attempts to perform inlining unconditionally and thus asserts
   /// if inlining will fail. All users /must/ check that a function is allowed
-  /// to be inlined using SILInliner::canInlineApplyAite before calling this
+  /// to be inlined using SILInliner::canInlineApplySite before calling this
   /// function.
   SILBasicBlock::iterator inlineFunction(SILFunction *calleeFunction,
                                          FullApplySite apply,