[Polly] Remove dependency of `Scop::getLastStmtFor(BB)` on `getStmtFor(BB)`. [NFC].

[nandini12396]

Summary

We are working towards removing uses of Scop::getStmtFor(BB). In this patch, we remove dependency of Scop::getLastStmtFor(BB) on getStmtFor(BB). To do so, we get the list of all statements corresponding to the BB and then fetch the last one.

[Meinersbur]

Looks good, with a single remark.

lib/Analysis/ScopInfo.cpp

4925–4926 ↗

(On Diff #107460)

This executes getStmtListFor(BB) for the same argument twice. Could you store its result in a variable for reuse?

[nandini12396]

Addressed comments.

polly/trunk/include/polly/ScopInfo.h

public:
 
   /// Get an isl string representing the invalid context.
   std::string getInvalidContextStr() const;
 
   /// Return the ScopStmt for the given @p BB or nullptr if there is
   ///        none.
   ScopStmt *getStmtFor(BasicBlock *BB) const;
 
+  /// Return the list of ScopStmts that represent the given @p BB.
+  ArrayRef<ScopStmt *> getStmtListFor(BasicBlock *BB) const;
+
   /// Return the last statement representing @p BB.
   ///
   /// Of the sequence of statements that represent a @p BB, this is the last one
   /// to be executed. It is typically used to determine which instruction to add
   /// a MemoryKind::PHI WRITE to. For this purpose, it is not strictly required
   /// to be executed last, only that the incoming value is available in it.
-  ScopStmt *getLastStmtFor(BasicBlock *BB) const { return getStmtFor(BB); }
+  ScopStmt *getLastStmtFor(BasicBlock *BB) const;
 
   /// Return the ScopStmt that represents the Region @p R, or nullptr if
   ///        it is not represented by any statement in this Scop.
   ScopStmt *getStmtFor(Region *R) const;
 
   /// Return the ScopStmt that represents @p RN; can return nullptr if
   ///        the RegionNode is not within the SCoP or has been removed due to
   ///        simplifications.

polly/trunk/lib/Analysis/ScopInfo.cpp

 ScopStmt *Scop::getStmtFor(BasicBlock *BB) const {
   auto StmtMapIt = StmtMap.find(BB);
   if (StmtMapIt == StmtMap.end())
     return nullptr;
   assert(StmtMapIt->second.size() == 1);
   return StmtMapIt->second.front();
 }
 
+ArrayRef<ScopStmt *> Scop::getStmtListFor(BasicBlock *BB) const {
+  auto StmtMapIt = StmtMap.find(BB);
+  if (StmtMapIt == StmtMap.end())
+    return {};
+  assert(StmtMapIt->second.size() == 1 &&
+         "Each statement corresponds to exactly one BB.");
+  return StmtMapIt->second;
+}
+
+ScopStmt *Scop::getLastStmtFor(BasicBlock *BB) const {
+  ArrayRef<ScopStmt *> StmtList = getStmtListFor(BB);
+  if (StmtList.size() > 0)
+    return StmtList.back();
+  return nullptr;
+}
+
 ScopStmt *Scop::getStmtFor(RegionNode *RN) const {
   if (RN->isSubRegion())
     return getStmtFor(RN->getNodeAs<Region>());
   return getStmtFor(RN->getNodeAs<BasicBlock>());
 }
 
 ScopStmt *Scop::getStmtFor(Region *R) const {
   ScopStmt *Stmt = getStmtFor(R->getEntry());