Make it explicit that MemoryLifetimeVerifier will not handle reborrows

Author: meg-gupta

lib/SIL/Utils/MemoryLocations.cpp

@@ -357,6 +357,11 @@ bool MemoryLocations::analyzeLocationUsesRecursively(SILValue V, unsigned locIdx
         if (!handleNonTrivialProjections && hasInoutArgument(ApplySite(user)))
           return false;
         break;
+      case SILInstructionKind::LoadBorrowInst:
+        // Reborrows are not handled
+        if (!cast<LoadBorrowInst>(user)->getUsersOfType<BranchInst>().empty())
+          return false;
+        break;
       case SILInstructionKind::InjectEnumAddrInst:
       case SILInstructionKind::SelectEnumAddrInst:
       case SILInstructionKind::ExistentialMetatypeInst:
@@ -367,7 +372,6 @@ bool MemoryLocations::analyzeLocationUsesRecursively(SILValue V, unsigned locIdx
       case SILInstructionKind::StoreInst:
       case SILInstructionKind::StoreBorrowInst:
       case SILInstructionKind::EndAccessInst:
-      case SILInstructionKind::LoadBorrowInst:
       case SILInstructionKind::DestroyAddrInst:
       case SILInstructionKind::CheckedCastAddrBranchInst:
       case SILInstructionKind::UncheckedRefCastAddrInst:

test/SIL/memory_lifetime_failures.sil

@@ -538,3 +538,32 @@ bb0(%0 : $Bool):
   %10 = tuple ()
   return %10 : $()
 }
+
+// MemoryLifetimeVerifier does not detect an error here due to reborrows
+sil [ossa] @test_load_borrow1 : $@convention(thin) (@in Optional<T>) -> () {
+bb0(%0 : $*Optional<T>):
+  destroy_addr %0 : $*Optional<T>
+  %1 = load_borrow %0 : $*Optional<T>
+  br bb1(%1 : $Optional<T>)
+
+bb1(%3 : @guaranteed $Optional<T>):
+  end_borrow %3 : $Optional<T>
+  br bb2
+
+bb2:
+  %r = tuple ()
+  return %r : $()
+}
+
+// CHECK: SIL memory lifetime failure in @test_load_borrow2: memory is not initialized, but should
+sil [ossa] @test_load_borrow2 : $@convention(thin) (@in Optional<T>) -> () {
+bb0(%0 : $*Optional<T>):
+  destroy_addr %0 : $*Optional<T>
+  %1 = load_borrow %0 : $*Optional<T>
+  end_borrow %1 : $Optional<T>
+  br bb1
+
+bb1:
+  %r = tuple ()
+  return %r : $()
+}