[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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@369327 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Transforms/IPO/Attributor.h b/include/llvm/Transforms/IPO/Attributor.h
index 484dd0c31e25f0803a97f4c0be66092a71461346..7e03e54fde5da08650e8719a4312234185b9e21c 100644 (file)
--- a/include/llvm/Transforms/IPO/Attributor.h
+++ b/include/llvm/Transforms/IPO/Attributor.h
@@ -890,10 +890,13 @@ struct IntegerState : public AbstractState {
   /// Inequality for IntegerState.
   bool operator!=(const IntegerState &R) const { return !(*this == R); }
 
-  /// "Clamp" this state with \p R. The result is the maximum of the known
-  /// information but the minimum of the assumed.
+  /// "Clamp" this state with \p R. The result is the minimum of the assumed
+  /// information but not less than what was known before.
+  ///
+  /// TODO: Consider replacing the operator with a call or using it only when
+  ///       we can also take the maximum of the known information, thus when
+  ///       \p R is not dependent on additional assumed state.
   IntegerState operator^=(const IntegerState &R) {
-    takeKnownMaximum(R.Known);
     takeAssumedMinimum(R.Assumed);
     return *this;
   }

diff --git a/lib/Transforms/IPO/Attributor.cpp b/lib/Transforms/IPO/Attributor.cpp
index 5ad9d4cb977a6db8bf1b9d8a833c9f4e4b8cde9f..ee3541b7c1db77f5849ef19cb716839c6574b333 100644 (file)
--- a/lib/Transforms/IPO/Attributor.cpp
+++ b/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);
   }