[SILGen] Added borrow scopes to alloc_boxes.

Because AllocBoxToStack is not able to transform every alloc_box into an
alloc_stack, it's necessary to add begin_borrow [lexical] to every
alloc_box in order to provide lexical scopes for those alloc_boxes which
will not be transformed into alloc_stacks.

Author: nate-chandler

lib/SILGen/ResultPlan.cpp

@@ -66,7 +66,13 @@ class IndirectOpenedSelfCleanup final : public Cleanup {
   void emit(SILGenFunction &SGF, CleanupLocation loc, ForUnwind_t forUnwind)
   override {
     assert(box && "buffer never emitted before activating cleanup?!");
-    SGF.B.createDeallocBox(loc, box);
+    auto theBox = box;
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      auto *bbi = cast<BeginBorrowInst>(theBox);
+      SGF.B.createEndBorrow(loc, bbi);
+      theBox = bbi->getOperand();
+    }
+    SGF.B.createDeallocBox(loc, theBox);
   }
 
   void dump(SILGenFunction &SGF) const override {
@@ -160,7 +166,10 @@ class IndirectOpenedSelfResultPlan final : public ResultPlan {
       SILBoxType::get(SGF.getASTContext(),
                       boxLayout,
                       layoutSubs));
-    
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      resultBox = SGF.B.createBeginBorrow(loc, resultBox, /*isLexical=*/true);
+    }
+
     // Complete the cleanup to deallocate this buffer later, after we're
     // finished with the argument.
     static_cast<IndirectOpenedSelfCleanup&>(SGF.Cleanups.getCleanup(handle))

lib/SILGen/SILGenApply.cpp

@@ -3505,7 +3505,13 @@ class DeallocateUninitializedBox : public Cleanup {
   DeallocateUninitializedBox(SILValue box) : box(box) {}
 
   void emit(SILGenFunction &SGF, CleanupLocation l, ForUnwind_t forUnwind) override {
-    SGF.B.createDeallocBox(l, box);
+    auto theBox = box;
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      auto *bbi = cast<BeginBorrowInst>(theBox);
+      SGF.B.createEndBorrow(l, bbi);
+      theBox = bbi->getOperand();
+    }
+    SGF.B.createDeallocBox(l, theBox);
   }
 
   void dump(SILGenFunction &SGF) const override {

lib/SILGen/SILGenDecl.cpp

@@ -297,7 +297,13 @@ class DeallocateUninitializedLocalVariable : public Cleanup {
 
   void emit(SILGenFunction &SGF, CleanupLocation l,
             ForUnwind_t forUnwind) override {
-    SGF.B.createDeallocBox(l, Box);
+    auto box = Box;
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      auto *bbi = cast<BeginBorrowInst>(box);
+      SGF.B.createEndBorrow(l, bbi);
+      box = bbi->getOperand();
+    }
+    SGF.B.createDeallocBox(l, box);
   }
 
   void dump(SILGenFunction &) const override {
@@ -360,6 +366,10 @@ class LocalVariableInitialization : public SingleBufferInitialization {
     if (kind)
       Box = SGF.B.createMarkUninitialized(decl, Box, kind.getValue());
 
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      Box = SGF.B.createBeginBorrow(decl, Box, /*isLexical=*/true);
+    }
+
     Addr = SGF.B.createProjectBox(decl, Box, 0);
 
     // Push a cleanup to destroy the local variable.  This has to be
@@ -1751,7 +1761,15 @@ void SILGenFunction::destroyLocalVariable(SILLocation silLoc, VarDecl *vd) {
   // For a heap variable, the box is responsible for the value. We just need
   // to give up our retain count on it.
   if (loc.box) {
-    B.emitDestroyValueOperation(silLoc, loc.box);
+    if (!getASTContext().SILOpts.supportsLexicalLifetimes(getModule())) {
+      B.emitDestroyValueOperation(silLoc, loc.box);
+      return;
+    }
+
+    auto *bbi = cast<BeginBorrowInst>(loc.box);
+    B.createEndBorrow(silLoc, bbi);
+    B.emitDestroyValueOperation(silLoc, bbi->getOperand());
+
     return;
   }
 

lib/SILGen/Scope.cpp

@@ -57,6 +57,9 @@ static void lifetimeExtendAddressOnlyRValueSubValues(
            "addresses must be address only.");
     auto boxTy = SILBoxType::get(v->getType().getASTType());
     SILValue box = SGF.B.createAllocBox(loc, boxTy);
+    if (SGF.getASTContext().SILOpts.supportsLexicalLifetimes(SGF.getModule())) {
+      box = SGF.B.createBeginBorrow(loc, box, /*isLexical=*/true);
+    }
     SILValue addr = SGF.B.createProjectBox(loc, box, 0);
     SGF.B.createCopyAddr(loc, v, addr, IsTake, IsInitialization);