commit 3a5e25278a632dd9c123595e714aa9ce081b1f0e
author Sanjoy Das <sanjoy@playingwithpointers.com> Tue Oct 17 01:03:56 2017 +0000
committer Sanjoy Das <sanjoy@playingwithpointers.com> Tue Oct 17 01:03:56 2017 +0000
tree 4a602e7f1e39eb616ad99c02bca4f912fc1dfe91
parent 57b7d4fad7111a2479d624eae6f0c8af684d0b99

Revert "[SCEV] Maintain and use a loop->loop invalidation dependency"

This reverts commit r315713.  It causes PR34968.

I think I know what the problem is, but I don't think I'll have time to fix it
this week.

llvm-svn: 315962

llvm/lib/Analysis/ScalarEvolution.cpp

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 6ef11cb..c69bd60 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6293,7 +6293,6 @@
   BackedgeTakenInfo Result =
       computeBackedgeTakenCount(L, /*AllowPredicates=*/true);
 
-  addToLoopUseLists(Result, L);
   return PredicatedBackedgeTakenCounts.find(L)->second = std::move(Result);
 }
 
@@ -6369,7 +6368,6 @@
   // recusive call to getBackedgeTakenInfo (on a different
   // loop), which would invalidate the iterator computed
   // earlier.
-  addToLoopUseLists(Result, L);
   return BackedgeTakenCounts.find(L)->second = std::move(Result);
 }
 
@@ -6407,14 +6405,8 @@
 
     auto LoopUsersItr = LoopUsers.find(CurrL);
     if (LoopUsersItr != LoopUsers.end()) {
-      for (auto LoopOrSCEV : LoopUsersItr->second) {
-        if (auto *S = LoopOrSCEV.dyn_cast<const SCEV *>())
-          forgetMemoizedResults(S);
-        else {
-          BackedgeTakenCounts.erase(LoopOrSCEV.get<const Loop *>());
-          PredicatedBackedgeTakenCounts.erase(LoopOrSCEV.get<const Loop *>());
-        }
-      }
+      for (auto *S : LoopUsersItr->second)
+        forgetMemoizedResults(S);
       LoopUsers.erase(LoopUsersItr);
     }
 
@@ -6559,34 +6551,6 @@
   return false;
 }
 
-static void findUsedLoopsInSCEVExpr(const SCEV *S,
-                                    SmallPtrSetImpl<const Loop *> &Result) {
-  struct FindUsedLoops {
-    SmallPtrSetImpl<const Loop *> &LoopsUsed;
-    FindUsedLoops(SmallPtrSetImpl<const Loop *> &LoopsUsed)
-        : LoopsUsed(LoopsUsed) {}
-    bool follow(const SCEV *S) {
-      if (auto *AR = dyn_cast<SCEVAddRecExpr>(S))
-        LoopsUsed.insert(AR->getLoop());
-      return true;
-    }
-
-    bool isDone() const { return false; }
-  };
-  FindUsedLoops F(Result);
-  SCEVTraversal<FindUsedLoops>(F).visitAll(S);
-}
-
-void ScalarEvolution::BackedgeTakenInfo::findUsedLoops(
-    ScalarEvolution &SE, SmallPtrSetImpl<const Loop *> &Result) const {
-  if (auto *S = getMax())
-    if (S != SE.getCouldNotCompute())
-      findUsedLoopsInSCEVExpr(S, Result);
-  for (auto &ENT : ExitNotTaken)
-    if (ENT.ExactNotTaken != SE.getCouldNotCompute())
-      findUsedLoopsInSCEVExpr(ENT.ExactNotTaken, Result);
-}
-
 ScalarEvolution::ExitLimit::ExitLimit(const SCEV *E)
     : ExactNotTaken(E), MaxNotTaken(E) {
   assert((isa<SCEVCouldNotCompute>(MaxNotTaken) ||
@@ -11070,6 +11034,21 @@
       ++I;
   }
 
+  auto RemoveSCEVFromBackedgeMap =
+      [S, this](DenseMap<const Loop *, BackedgeTakenInfo> &Map) {
+        for (auto I = Map.begin(), E = Map.end(); I != E;) {
+          BackedgeTakenInfo &BEInfo = I->second;
+          if (BEInfo.hasOperand(S, this)) {
+            BEInfo.clear();
+            Map.erase(I++);
+          } else
+            ++I;
+        }
+      };
+
+  RemoveSCEVFromBackedgeMap(BackedgeTakenCounts);
+  RemoveSCEVFromBackedgeMap(PredicatedBackedgeTakenCounts);
+
   // TODO: There is a suspicion that we only need to do it when there is a
   // SCEVUnknown somewhere inside S. Need to check this.
   if (EraseExitLimit)
@@ -11079,19 +11058,22 @@
 }
 
 void ScalarEvolution::addToLoopUseLists(const SCEV *S) {
-  SmallPtrSet<const Loop *, 8> LoopsUsed;
-  findUsedLoopsInSCEVExpr(S, LoopsUsed);
-  for (auto *L : LoopsUsed)
-    LoopUsers[L].push_back({S});
-}
+  struct FindUsedLoops {
+    SmallPtrSet<const Loop *, 8> LoopsUsed;
+    bool follow(const SCEV *S) {
+      if (auto *AR = dyn_cast<SCEVAddRecExpr>(S))
+        LoopsUsed.insert(AR->getLoop());
+      return true;
+    }
 
-void ScalarEvolution::addToLoopUseLists(
-    const ScalarEvolution::BackedgeTakenInfo &BTI, const Loop *L) {
-  SmallPtrSet<const Loop *, 8> LoopsUsed;
-  BTI.findUsedLoops(*this, LoopsUsed);
+    bool isDone() const { return false; }
+  };
 
-  for (auto *UsedL : LoopsUsed)
-    LoopUsers[UsedL].push_back({L});
+  FindUsedLoops F;
+  SCEVTraversal<FindUsedLoops>(F).visitAll(S);
+
+  for (auto *L : F.LoopsUsed)
+    LoopUsers[L].push_back(S);
 }
 
 void ScalarEvolution::verify() const {