[Polly][Refactor][NFC] Allow to nicely bail from ScopInfo.

[jdoerfert]

Summary

Each SCoP statement has a flag to indicate if the construction was
successful and if one statement couldn't be constructed the SCoP
is invalidated and removed.

[jdoerfert]

Won't be merged.

include/polly/ScopInfo.h

class ScopStmt {
   /// @brief The loop induction variables surrounding the statement.
   ///
   /// This information is only needed for final code generation.
   std::vector<PHINode *> IVS;
   std::vector<Loop *> NestLoops;
 
   std::string BaseName;
 
+  /// @brief Flag to remember errors during the construction of the statement.
+  bool IsValid;
+
   /// Build the statement.
   //@{
   __isl_give isl_set *buildConditionSet(const Comparison &Cmp);
   __isl_give isl_set *addConditionsToDomain(__isl_take isl_set *Domain,
                                             TempScop &tempScop,
                                             const Region &CurRegion);
   __isl_give isl_set *addLoopBoundsToDomain(__isl_take isl_set *Domain,
                                             TempScop &tempScop);
collectCandiateReductionLoads(MemoryAccess *StoreMA,
                                 llvm::SmallVectorImpl<MemoryAccess *> &Loads);
   //@}
 
   /// Create the ScopStmt from a BasicBlock.
   ScopStmt(Scop &parent, TempScop &tempScop, const Region &CurRegion,
            BasicBlock &bb, SmallVectorImpl<Loop *> &NestLoops,
            SmallVectorImpl<unsigned> &Scatter);
 
+  /// @brief Check if the construction went without an error.
+  bool isValid() const { return IsValid; }
+
   friend class Scop;
 
 public:
   ~ScopStmt();
 
   /// @brief Get an isl_ctx pointer.
   isl_ctx *getIslCtx() const;
 
private:
   void buildContext();
 
   /// @brief Add the bounds of the parameters to the context.
   void addParameterBounds();
 
   /// @brief Simplify the assumed context.
   void simplifyAssumedContext();
 
+  /// @brief Check if all statements are valid or if at least one is not.
+  bool statementsAreValid() const {
+    for (ScopStmt *Stmt : *this)
+      if (!Stmt->isValid())
+        return false;
+    return true;
+  }
+
   /// Build the Scop and Statement with precalculated scop information.
   void buildScop(TempScop &TempScop, const Region &CurRegion,
                  // Loops in Scop containing CurRegion
                  SmallVectorImpl<Loop *> &NestLoops,
                  // The scattering numbers
                  SmallVectorImpl<unsigned> &Scatter, LoopInfo &LI);
 
   /// @name Helper function for printing the Scop.

lib/Analysis/ScopInfo.cpp

__isl_give isl_set *ScopStmt::buildDomain(TempScop &tempScop,
   Domain = isl_set_set_tuple_id(Domain, Id);
 
   return Domain;
 }
 
 ScopStmt::ScopStmt(Scop &parent, TempScop &tempScop, const Region &CurRegion,
                    BasicBlock &bb, SmallVectorImpl<Loop *> &Nest,
                    SmallVectorImpl<unsigned> &Scatter)
-    : Parent(parent), BB(&bb), IVS(Nest.size()), NestLoops(Nest.size()) {
+    : Parent(parent), BB(&bb), IVS(Nest.size()), NestLoops(Nest.size()),
+      IsValid(true) {
   // Setup the induction variables.
   for (unsigned i = 0, e = Nest.size(); i < e; ++i) {
     if (!SCEVCodegen) {
       PHINode *PN = Nest[i]->getCanonicalInductionVariable();
       assert(PN && "Non canonical IV in Scop!");
       IVS[i] = PN;
     }
     NestLoops[i] = Nest[i];
bool ScopInfo::runOnRegion(Region *R, RGPassManager &RGM) {
   TempScop *tempScop = getAnalysis<TempScopInfo>().getTempScop(R);
 
   // This region is no Scop.
   if (!tempScop) {
     scop = 0;
     return false;
   }
 
-  // Statistics.
-  ++ScopFound;
-  if (tempScop->getMaxLoopDepth() > 0)
-    ++RichScopFound;
-
   scop = new Scop(*tempScop, LI, SE, ctx);
 
-  if (!PollyUseRuntimeAliasChecks)
-    return false;
+  // If a problem occurs while building the SCoP statements or the alias groups
+  // we need to delete this SCoP and pretend it wasn't valid in the first place.
+  bool Valid = scop->statementsAreValid();
+  if (PollyUseRuntimeAliasChecks)
+    Valid = Valid && scop->buildAliasGroups(AA);
+
+  if (!Valid) {
+    DEBUG(dbgs() << "There was a problem during the construction of the SCoP. "
+                    "It will not be considered for optimization. Possible "
+                    "reasons include:\n\tRuntime alias checks were to "
+                    "complex/contained to many parameters.\n\t\t Use "
+                    "--polly-rtc-max-parameters=X\n\tto adjust the maximal "
+                    "number of parameters allowed (for the price of compile "
+                    "time).");
 
-  // If a problem occurs while building the alias groups we need to delete
-  // this SCoP and pretend it wasn't valid in the first place.
-  if (scop->buildAliasGroups(AA))
+    delete scop;
+    scop = nullptr;
     return false;
+  }
 
-  --ScopFound;
+  // Statistics after we know the SCoP is valid.
+  ++ScopFound;
   if (tempScop->getMaxLoopDepth() > 0)
-    --RichScopFound;
-
-  DEBUG(dbgs()
-        << "\n\nNOTE: Run time checks for " << scop->getNameStr()
-        << " could not be created as the number of parameters involved is too "
-           "high. The SCoP will be "
-           "dismissed.\nUse:\n\t--polly-rtc-max-parameters=X\nto adjust the "
-           "maximal number of parameters but be advised that the compile time "
-           "might increase exponentially.\n\n");
+    ++RichScopFound;
 
-  delete scop;
-  scop = nullptr;
   return false;
 }
 
 char ScopInfo::ID = 0;
 
 Pass *polly::createScopInfoPass() { return new ScopInfo(); }
 
 INITIALIZE_PASS_BEGIN(ScopInfo, "polly-scops",