[region-isolation] Rely on our classification of lookthrough or not to find underlying tracked object values rather than delegating to other analysis helpers.

There is no guarantee that these other helpers properly model lookthrough as our
model does. This ensures that this routine is always in sync with how we define
lookthrough in our model.

The problem with the old approach can be seen in how we handled move_value. The
model and the later code knew correctly that they should not look through
move_value that is marked as [var_decl]. But this other analysis code did not.
This with the tree today should not have any impact. But with the fix I am doing
now (fixing nonisolated(unsafe)) and later isolation history this will become a
problem.

(cherry picked from commit b66cfcc)

Author: gottesmm

lib/SILOptimizer/Analysis/RegionAnalysis.cpp

@@ -128,6 +128,16 @@ struct UseDefChainVisitor
                                              cast->getFunction()))
       return SILValue();
 
+    // Do not look through begin_borrow [var_decl]. They are start new semantic
+    // values.
+    //
+    // This only comes up if a codegen pattern occurs where the debug
+    // information is place on a debug_value instead of the alloc_box.
+    if (auto *bbi = dyn_cast<BeginBorrowInst>(cast)) {
+      if (bbi->isFromVarDecl())
+        return SILValue();
+    }
+
     // If we do not have an identity cast, mark this as a merge.
     isMerge |= castType != AccessStorageCast::Identity;
 
@@ -305,11 +315,6 @@ static SILValue getUnderlyingTrackedObjectValue(SILValue value) {
   while (true) {
     SILValue temp = result;
 
-    temp = stripSinglePredecessorArgs(temp);
-    temp = stripAddressProjections(temp);
-    temp = stripIndexingInsts(temp);
-    temp = lookThroughOwnershipInsts(temp);
-
     if (auto *svi = dyn_cast<SingleValueInstruction>(temp)) {
       if (isStaticallyLookThroughInst(svi)) {
         temp = svi->getOperand(0);
@@ -356,6 +361,11 @@ static SILValue getUnderlyingTrackedObjectValue(SILValue value) {
 }
 
 static UnderlyingTrackedValueInfo getUnderlyingTrackedValue(SILValue value) {
+  // Look through a project_box, so that we process it like its operand object.
+  if (auto *pbi = dyn_cast<ProjectBoxInst>(value)) {
+    value = pbi->getOperand();
+  }
+
   if (!value->getType().isAddress()) {
     SILValue underlyingValue = getUnderlyingTrackedObjectValue(value);