Factor out some of the code for updating old SCEVUnknown values, and

extend it to handle the case where multiple RAUWs affect a single
SCEVUnknown.

Add a ScalarEvolution unittest to test for this situation.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109705 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 45 insertions, 29 deletions

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 7612f43f71..964093b069 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3660,29 +3660,59 @@ void ScalarEvolution::forgetLoop(const Loop *L) {
   }
 }
 
-/// forgetValue - This method should be called by the client when it has
-/// changed a value in a way that may effect its value, or which may
-/// disconnect it from a def-use chain linking it to a loop.
-void ScalarEvolution::forgetValue(Value *V) {
-  // If there's a SCEVUnknown tying this value into the SCEV
-  // space, remove it from the folding set map. The SCEVUnknown
-  // object and any other SCEV objects which reference it
-  // (transitively) remain allocated, effectively leaked until
-  // the underlying BumpPtrAllocator is freed.
-  //
+/// forgetSCEVUnknown - V is being deleted or RAUW'd; remove the
+/// SCEVUnknown for it from the uniquing map, and optionally
+/// clear its contents to point to a replacement value.
+void ScalarEvolution::forgetSCEVUnknown(Value *V, Value *NewV) {
   // This permits SCEV pointers to be used as keys in maps
   // such as the ValuesAtScopes map.
+
+  // Check for an exisitng SCEVUnknown for V in the uniquing map.
   FoldingSetNodeID ID;
   ID.AddInteger(scUnknown);
   ID.AddPointer(V);
   void *IP;
   if (SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) {
+    // Remove the old SCEVUnknown from the uniquing map, effectively
+    // leaking it from subsequent use by ScalarEvolution. There
+    // may be existing SCEVs live which still point to it though.
     UniqueSCEVs.RemoveNode(S);
 
-    // This isn't necessary, but we might as well remove the
-    // value from the ValuesAtScopes map too.
-    ValuesAtScopes.erase(S);
+    // If there's a replacement value, update the old SCEVUnknowns
+    // so that SCEVs which still point to it see the new value.
+    if (NewV) {
+      // Update the old SCEVUnknown and all SCEVUnknowns on its update list
+      // to point to NewV instead of V.
+      for (SCEVUnknown *U = cast<SCEVUnknown>(S); U; U = U->UpdateList) {
+        assert(U->V == V && "SCEVUnknown update list is inconsistent!");
+        U->V = NewV;
+      }
+
+      // Check for an existing SCEVUnknown for NewV in the uniquing map.
+      ID.clear();
+      ID.AddInteger(scUnknown);
+      ID.AddPointer(NewV);
+      if (SCEV *NewS = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) {
+        // The uniquing map already had an entry for the new
+        // value. Append the old SCEVUnknown (and its update list) to the
+        // new SCEVUnknown's update list.
+        cast<SCEVUnknown>(NewS)->getUpdateListBack()->UpdateList =
+          cast<SCEVUnknown>(S);
+      } else {
+        // The uniquing map did not have an entry for the new
+        // value yet. Set the old SCEVUnknown, which has now been
+        // updated, to be the SCEVUnknown in the uniquing map.
+        UniqueSCEVs.InsertNode(S, IP);
+      }
+    }
   }
+}
+
+/// forgetValue - This method should be called by the client when it has
+/// changed a value in a way that may effect its value, or which may
+/// disconnect it from a def-use chain linking it to a loop.
+void ScalarEvolution::forgetValue(Value *V) {
+  forgetSCEVUnknown(V, 0);
 
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return;
@@ -5692,24 +5722,10 @@ void ScalarEvolution::SCEVCallbackVH::deleted() {
 
 void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *V) {
   assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!");
-
   Value *Old = getValPtr();
 
-  // If there's a SCEVUnknown tying this value into the SCEV
-  // space, replace the SCEVUnknown's value with the new value
-  // for the benefit of any SCEVs still referencing it, and
-  // and remove it from the folding set map so that new scevs
-  // don't reference it.
-  FoldingSetNodeID ID;
-  ID.AddInteger(scUnknown);
-  ID.AddPointer(Old);
-  void *IP;
-  if (SCEVUnknown *S = cast_or_null<SCEVUnknown>(
-        SE->UniqueSCEVs.FindNodeOrInsertPos(ID, IP))) {
-    S->V = V;
-    SE->UniqueSCEVs.RemoveNode(S);
-    SE->ValuesAtScopes.erase(S);
-  }
+  // First, update existing SCEVUnknowns.
+  SE->forgetSCEVUnknown(Old, V);
 
   // Forget all the expressions associated with users of the old value,
   // so that future queries will recompute the expressions using the new