[region-isolation] Only perform merge assignment if we capture an address in a partial_apply rather than if we send it to any function apply.

Semantically these are the only cases where we would want to force an address to
be merged. Some notes:

1. When we have a box, the project_box is considered to come from the box and is
considered non uniquely identified.

2. The only place this was really triggering was when we created temporary
partial applies to pass to a function when using address only types. Since this
temporaries are never reassigned to, there isn't any reason to require them to
be merged.

3. In the case where we have an alloc_stack grabbed by a partial_apply, we still
appropriately merge.

Author: gottesmm

lib/SILOptimizer/Mandatory/SendNonSendable.cpp

@@ -17,6 +17,7 @@
 #include "swift/SIL/BasicBlockData.h"
 #include "swift/SIL/BasicBlockDatastructures.h"
 #include "swift/SIL/MemAccessUtils.h"
+#include "swift/SIL/NodeDatastructures.h"
 #include "swift/SIL/OwnershipUtils.h"
 #include "swift/SIL/SILBasicBlock.h"
 #include "swift/SIL/SILFunction.h"
@@ -49,10 +50,6 @@ static bool SILApplyCrossesIsolation(const SILInstruction *inst) {
   return false;
 }
 
-static bool isApplyInst(SILInstruction &inst) {
-  return ApplySite::isa(&inst) || isa<BuiltinInst>(inst);
-}
-
 static AccessStorage getAccessStorageFromAddr(SILValue value) {
   assert(value->getType().isAddress());
   auto accessStorage = AccessStorage::compute(value);
@@ -435,13 +432,26 @@ class PartitionOpTranslator {
 
     for (auto &block : *function) {
       for (auto &inst : block) {
-        if (isApplyInst(inst)) {
-          // add all nonsendable, uniquely identified arguments to applications
-          // to capturedUIValues, because applications capture them
+        if (auto *pai = dyn_cast<PartialApplyInst>(&inst)) {
+          // If we find an address or a box of a non-Sendable type that is
+          // passed to a partial_apply, mark the value's representative as being
+          // uniquely identified and captured.
           for (SILValue val : inst.getOperandValues()) {
-            if (val->getType().isAddress()) {
+            if (val->getType().isAddress() &&
+                isNonSendableType(val->getType())) {
               auto trackVal = getTrackableValue(val, true);
+              (void)trackVal;
               LLVM_DEBUG(trackVal.print(llvm::dbgs()));
+              continue;
+            }
+
+            if (auto *pbi = dyn_cast<ProjectBoxInst>(val)) {
+              if (isNonSendableType(
+                      pbi->getType().getSILBoxFieldType(function))) {
+                auto trackVal = getTrackableValue(val, true);
+                (void)trackVal;
+                continue;
+              }
             }
           }
         }