[Exclusivity] Check that accesses are well-formed during diagnostics.

This can help catch assumptions in current implementation during testing.
It does not need to be merged to 4.0.

Author: atrick

lib/SILOptimizer/Mandatory/DiagnoseStaticExclusivity.cpp

@@ -454,7 +454,7 @@ static AccessedStorage findAccessedStorage(SILValue Source) {
 
     if (auto *REA = dyn_cast<RefElementAddrInst>(Iter)) {
       // Do a best-effort to find the identity of the object being projected
-      // from. It is OK to unsound here (i.e., miss when two ref_element_addrs
+      // from. It is OK to be unsound here (i.e. miss when two ref_element_addrs
       // actually refer the same address) because these will be dynamically
       // checked.
       SILValue Object = findUnderlyingObject(REA->getOperand());
@@ -463,18 +463,27 @@ static AccessedStorage findAccessedStorage(SILValue Source) {
       return AccessedStorage(AccessedStorageKind::ClassProperty, OP);
     }
 
-    if (isa<AllocBoxInst>(Iter) || isa<BeginAccessInst>(Iter) ||
-        isa<SILFunctionArgument>(Iter)) {
-      // Treat the instruction itself as the identity of the storage being
-      // being accessed.
+    switch (Iter->getKind()) {
+    case ValueKind::AllocBoxInst:
+      // An AllocBox is a fully identified memory location.
+      LLVM_FALLTHROUGH;
+    case ValueKind::BeginAccessInst:
+      // The current access is nested within another access.
+      // View the outer access as a separate location because nested accesses do
+      // not conflict with each other.
+      LLVM_FALLTHROUGH;
+    case ValueKind::SILFunctionArgument:
+      // A function argument is effectively a nested access, enforced
+      // independently in the caller and callee.
+      LLVM_FALLTHROUGH;
+    case ValueKind::PointerToAddressInst:
+      // An addressor provides access to a global or class property via a
+      // RawPointer. Calling the address casts that raw pointer to an address.
       return AccessedStorage(Iter);
+    default:
+      DEBUG(llvm::dbgs() << "Bad memory access source: " << Iter);
+      llvm_unreachable("Unexpected access source.");
     }
-
-    // For now we're still allowing arbitrary addresses here. Once
-    // we start doing a best-effort static check for dynamically-enforced
-    // accesses we should lock this down to only recognized sources.
-    assert(Iter->getType().isAddress() || Iter->getType().is<SILBoxType>());
-    return AccessedStorage(Iter);
   }
 }