Make sure we always have a SILFunction for region-based isolation checking

Some values (such as `undef`) might not be associated with a function.

Author: DougGregor

include/swift/SILOptimizer/Analysis/RegionAnalysis.h

@@ -299,7 +299,11 @@ class RegionAnalysisValueMap {
   /// This only includes function arguments.
   std::vector<TrackableValueID> neverTransferredValueIDs;
 
+  SILFunction *fn;
+
 public:
+  RegionAnalysisValueMap(SILFunction *fn) : fn(fn) { }
+
   /// Returns the value for this instruction if it isn't a fake "represenative
   /// value" to inject actor isolatedness. Asserts in such a case.
   SILValue getRepresentative(Element trackableValueID) const;

lib/SILOptimizer/Analysis/RegionAnalysis.cpp

@@ -2751,8 +2751,9 @@ static bool canComputeRegionsForFunction(SILFunction *fn) {
 
 RegionAnalysisFunctionInfo::RegionAnalysisFunctionInfo(
     SILFunction *fn, PostOrderFunctionInfo *pofi)
-    : allocator(), fn(fn), translator(), ptrSetFactory(allocator),
-      blockStates(), pofi(pofi), solved(false), supportedFunction(true) {
+    : allocator(), fn(fn), valueMap(fn), translator(),
+      ptrSetFactory(allocator), blockStates(), pofi(pofi), solved(false),
+      supportedFunction(true) {
   // Before we do anything, make sure that we support processing this function.
   //
   // NOTE: See documentation on supportedFunction for criteria.
@@ -2954,7 +2955,7 @@ TrackableValue RegionAnalysisValueMap::getTrackableValue(
   }
 
   // Otherwise refer to the oracle.
-  if (!isNonSendableType(value->getType(), value->getFunction()))
+  if (!isNonSendableType(value->getType(), fn))
     iter.first->getSecond().addFlag(TrackableValueFlag::isSendable);
 
   // Check if our base is a ref_element_addr from an actor. In such a case,