[polly] r224459 - Dead code elimination: Update dependences after eliminating code

[Tobias Grosser]

Author: grosser
Date: Wed Dec 17 15:13:55 2014
New Revision: 224459

URL: http://llvm.org/viewvc/llvm-project?rev=224459&view=rev
Log:
Dead code elimination: Update dependences after eliminating code

Without updating dependences we may lose implicit transitive dependences for
which all explicit dependences have gone through the statement iterations we
have just eliminated.

No test case. We should probably implement a -verify-dependences option.

This fixes llvm.org/PR21227

Modified:
    polly/trunk/include/polly/Dependences.h
    polly/trunk/lib/Analysis/Dependences.cpp
    polly/trunk/lib/Transform/DeadCodeElimination.cpp

Modified: polly/trunk/include/polly/Dependences.h
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/include/polly/Dependences.h?rev=224459&r1=224458&r2=224459&view=diff
==============================================================================
--- polly/trunk/include/polly/Dependences.h (original)
+++ polly/trunk/include/polly/Dependences.h Wed Dec 17 15:13:55 2014
@@ -121,12 +121,17 @@ public:
     return ReductionDependences;
   }
 
+  /// @brief Recompute dependences from schedule and memory accesses.
+  void recomputeDependences();
+
   bool runOnScop(Scop &S);
   void printScop(raw_ostream &OS) const;
   virtual void releaseMemory();
   virtual void getAnalysisUsage(AnalysisUsage &AU) const;
 
 private:
+  Scop *S;
+
   /// @brief The different kinds of dependences we calculate.
   isl_union_map *RAW;
   isl_union_map *WAR;

Modified: polly/trunk/lib/Analysis/Dependences.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/Dependences.cpp?rev=224459&r1=224458&r2=224459&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/Dependences.cpp (original)
+++ polly/trunk/lib/Analysis/Dependences.cpp Wed Dec 17 15:13:55 2014
@@ -432,10 +432,14 @@ void Dependences::calculateDependences(S
   DEBUG(printScop(dbgs()));
 }
 
-bool Dependences::runOnScop(Scop &S) {
+void Dependences::recomputeDependences() {
   releaseMemory();
-  calculateDependences(S);
+  calculateDependences(*S);
+}
 
+bool Dependences::runOnScop(Scop &ScopVar) {
+  S = &ScopVar;
+  recomputeDependences();
   return false;
 }
 

Modified: polly/trunk/lib/Transform/DeadCodeElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Transform/DeadCodeElimination.cpp?rev=224459&r1=224458&r2=224459&view=diff
==============================================================================
--- polly/trunk/lib/Transform/DeadCodeElimination.cpp (original)
+++ polly/trunk/lib/Transform/DeadCodeElimination.cpp Wed Dec 17 15:13:55 2014
@@ -151,7 +151,13 @@ bool DeadCodeElim::eliminateDeadCode(Sco
   isl_union_map_free(Dep);
   isl_union_set_free(OriginalDomain);
 
-  return S.restrictDomains(isl_union_set_coalesce(Live));
+  bool Changed = S.restrictDomains(isl_union_set_coalesce(Live));
+
+  // FIXME: We can probably avoid the recomputation of all dependences by
+  // updating them explicitly.
+  if (Changed)
+    D->recomputeDependences();
+  return Changed;
 }
 
 bool DeadCodeElim::runOnScop(Scop &S) {