[DebugInfo] Fix var info after DeadObjectElimination

The scope of a store has to be the variable's scope.
The type should be set to the element's type, and only if not already set.
The variable's location should be set.

(cherry picked from commit 7c9676e)

Author: Snowy1803

lib/SILOptimizer/Transforms/DeadObjectElimination.cpp

@@ -854,7 +854,10 @@ void DeadObjectElimination::salvageDebugInfo(SILInstruction *toBeRemoved) {
   if (!varInfo)
     return;
 
-  SILBuilderWithScope Builder(SI);
+  // Note: The instruction should logically be in SI's scope.
+  // However, LLVM does not support variables and stores in different scopes,
+  // so we use the variable's scope.
+  SILBuilder Builder(SI, varInfo->Scope);
   Builder.createDebugValue(SI->getLoc(), SI->getSrc(), *varInfo);
 }
 
@@ -866,7 +869,11 @@ DeadObjectElimination::buildDIExpression(SILInstruction *current) {
     auto var = dvci->getVarInfo();
     if (!var)
       return {};
-    var->Type = dvci->getType();
+    if (!var->Type)
+      var->Type = dvci->getElementType();
+    var->Loc = dvci->getVarLoc();
+    if (!var->Scope)
+      var->Scope = dvci->getDebugScope();
     return var;
   }
   if (auto *tupleAddr = dyn_cast<TupleElementAddrInst>(current)) {