[ScopInfo] Introduce tryGetValueStored

[grosser]

Summary

This makes code more readable and allows to reuse this functionality in
the future at other places.

Suggested-by Michael Kruse in post-commit review of r307660.

[Meinersbur]

include/polly/ScopInfo.h

899

[Serious] Must be isAnyPHIKind(). AccessValue of ExitPHIs are also only the PHINode itself, not the value written.

include/polly/ScopInfo.h

public:
   static const std::string getReductionOperatorStr(ReductionType RT);
 
   /// Return the element type of the accessed array wrt. this access.
   Type *getElementType() const { return ElementType; }
 
   /// Return the access value of this memory access.
   Value *getAccessValue() const { return AccessValue; }
 
+  /// Return llvm::Value that is stored by this access, if available.
+  ///
+  /// PHI nodes may not have a unique value available that is stored, as in
+  /// case of region statements one out of possibly several llvm::Values
+  /// might be stored. In this case nullptr is returned.
+  Value *tryGetValueStored() {
+    assert(isWrite() && "Only write statement store values");
+    if (isPHIKind()) {
+      if (Incoming.size() == 1)
+        return Incoming[0].second;
+      return nullptr;
+    }
+    return AccessValue;
+  }
+
   /// Return the access instruction of this memory access.
   Instruction *getAccessInstruction() const { return AccessInstruction; }
 
   /// Return the number of access function subscript.
   unsigned getNumSubscripts() const { return Subscripts.size(); }
 
   /// Return the access function subscript in the dimension @p Dim.
   const SCEV *getSubscript(unsigned Dim) const { return Subscripts[Dim]; }

lib/Transform/Simplify.cpp

for (auto &Stmt : *S) {
       for (auto *WA : Stmt) {
         if (!WA->isMustWrite())
           continue;
         if (!WA->isLatestArrayKind())
           continue;
         if (!isa<StoreInst>(WA->getAccessInstruction()) && !WA->isPHIKind())
           continue;
 
-        auto ReadingValue = WA->getAccessValue();
-
-        if (WA->isPHIKind()) {
-          PHINode *PHI = cast<PHINode>(WA->getAccessValue());
-          BasicBlock *BB = Stmt.getBasicBlock();
-          ReadingValue = PHI->getIncomingValueForBlock(BB);
-        }
+        llvm::Value *ReadingValue = WA->tryGetValueStored();
 
         if (!ReadingValue)
           continue;
 
         auto RA = getReadAccessForValue(&Stmt, ReadingValue);
         if (!RA)
           continue;
         if (!RA->isLatestArrayKind())