[Attributor] Fix the "clamp" operator

The clamp operator should not take the known of the given state as the
known is potentially based on assumed information. This also adds TODOs
to guide improvements.

llvm-svn: 369327

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 5ad9d4cb977..ee3541b7c1d 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -526,6 +526,8 @@ struct AAReturnedFromReturnedValues : public AAType {
   ChangeStatus updateImpl(Attributor &A) override {
     StateType S;
     clampReturnedValueStates<AAType, StateType>(A, *this, S);
+    // TODO: If we know we visited all returned values, thus no are assumed
+    // dead, we can take the known information from the state T.
     return clampStateAndIndicateChange<StateType>(this->getState(), S);
   }
 };
@@ -585,6 +587,8 @@ struct AAArgumentFromCallSiteArguments : public AAType {
   ChangeStatus updateImpl(Attributor &A) override {
     StateType S;
     clampCallSiteArgumentStates<AAType, StateType>(A, *this, S);
+    // TODO: If we know we visited all incoming values, thus no are assumed
+    // dead, we can take the known information from the state T.
     return clampStateAndIndicateChange<StateType>(this->getState(), S);
   }
 };
@@ -2265,6 +2269,8 @@ struct AAAlignFloating : AAAlignImpl {
                                                    VisitValueCB))
       indicatePessimisticFixpoint();
 
+    // TODO: If we know we visited all incoming values, thus no are assumed
+    // dead, we can take the known information from the state T.
     return clampStateAndIndicateChange(getState(), T);
   }