ClosureLifetimeFixup review feedback

Author: atrick

include/swift/SILOptimizer/Utils/InstOptUtils.h

@@ -281,7 +281,14 @@ void releasePartialApplyCapturedArg(
     SILParameterInfo paramInfo,
     InstModCallbacks callbacks = InstModCallbacks());
 
-/// Insert destroys of captured arguments of partial_apply [stack].
+/// Insert destroys of captured arguments of partial_apply [stack]. \p builder
+/// indicates a position at which the closure's lifetime ends.
+///
+/// The \p getValueToDestroy callback allows the caller to handle some captured
+/// arguments specially. For example, ClosureLifetimeFixup generates borrow
+/// scopes for captured arguments; each getValueToDestroy callback then inserts
+/// the corresponding end_borrow and returns the owned operand of the borrow,
+/// which will then be destroyed as usual.
 void insertDestroyOfCapturedArguments(
     PartialApplyInst *pai, SILBuilder &builder,
     llvm::function_ref<SILValue(SILValue)> getValueToDestroy =

lib/SILOptimizer/Mandatory/ClosureLifetimeFixup.cpp

@@ -619,7 +619,6 @@ static SILValue tryRewriteToPartialApplyStack(
     if (!argTy.isAddress() && !argTy.isTrivial(*cvt->getFunction())) {
       SILValue argValue = arg.get();
       bool foundNoImplicitCopy = false;
-      //!!!
       if (auto *mmci = dyn_cast<MoveOnlyWrapperToCopyableValueInst>(argValue)) {
         if (mmci->hasOwnedInitialKind() && mmci->hasOneUse()) {
           foundNoImplicitCopy = true;