Avoid optimizing lexical borrow scopes in DCE

Author: meg-gupta

lib/SILOptimizer/Transforms/DeadCodeElimination.cpp

@@ -303,7 +303,10 @@ void DCE::markLive() {
         }
         // Populate reborrowDependencies for this borrow
         findReborrowDependencies(borrowInst);
-        if (hasPointerEscape(BorrowedValue(borrowInst))) {
+        // Don't optimize a borrow scope if it is lexical or has a pointer
+        // escape.
+        if (borrowInst->isLexical() ||
+            hasPointerEscape(BorrowedValue(borrowInst))) {
           // Visit all end_borrows and mark them live
           visitTransitiveEndBorrows(borrowInst, [&](EndBorrowInst *endBorrow) {
             markInstructionLive(endBorrow);