Index: lib/Transforms/Scalar/CallSiteSplitting.cpp
===================================================================
--- lib/Transforms/Scalar/CallSiteSplitting.cpp
+++ lib/Transforms/Scalar/CallSiteSplitting.cpp
@@ -97,8 +97,12 @@
                                   Constant *ConstValue) {
   unsigned ArgNo = 0;
   for (auto &I : CS.args()) {
-    if (&*I == Op)
+    if (&*I == Op) {
+      // It is possible we have already added the non-null attribute to the
+      // parameter by using an earlier constraining condition.
+      CS.removeParamAttr(ArgNo, Attribute::NonNull);
       CS.setArgument(ArgNo, ConstValue);
+    }
     ++ArgNo;
   }
 }
Index: test/Transforms/CallSiteSplitting/callsite-split.ll
===================================================================
--- test/Transforms/CallSiteSplitting/callsite-split.ll
+++ test/Transforms/CallSiteSplitting/callsite-split.ll
@@ -35,6 +35,38 @@
   ret void
 }
 
+; Make sure we remove the non-nullness on constant paramater.
+;
+;CHECK-LABEL: @caller2
+;CHECK-LABEL: Top1.split:
+;CHECK: call void @callee(%struct.bitmap* inttoptr (i64 4643 to %struct.bitmap*), %struct.bitmap* inttoptr (i64 4643 to %struct.bitmap*), %struct.bitmap* %b_elt, i1 false)
+
+define void @caller2(i1 %c, %struct.bitmap* %a_elt, %struct.bitmap* %b_elt) {
+entry:
+  br label %Top0
+
+Top0:
+  %tobool1 = icmp eq %struct.bitmap* %a_elt, inttoptr (i64 4643 to  %struct.bitmap*) 
+  br i1 %tobool1, label %Top1, label %NextCond
+
+Top1:
+  %tobool2 = icmp ne %struct.bitmap* %a_elt, null
+  br i1 %tobool2, label %CallSiteBB, label %NextCond
+
+NextCond:
+  %cmp = icmp ne %struct.bitmap* %b_elt, null
+  br i1 %cmp, label %CallSiteBB, label %End
+
+CallSiteBB:
+  %p = phi i1 [0, %Top1], [%c, %NextCond]
+  call void @callee(%struct.bitmap* %a_elt, %struct.bitmap* %a_elt, %struct.bitmap* %b_elt, i1 %p)
+  br label %End
+
+End:
+  ret void
+}
+
+
 define void @callee(%struct.bitmap* %dst_elt, %struct.bitmap* %a_elt, %struct.bitmap* %b_elt, i1 %c) {
 entry:
   %tobool = icmp ne %struct.bitmap* %a_elt, null
@@ -68,7 +100,7 @@
 declare void @dummy1(%struct.bitmap*, %struct.bitmap*, %struct.bitmap*, %struct.bitmap*, %struct.bitmap*, %struct.bitmap*)
 
 
-;CHECK-LABEL: @caller2
+;CHECK-LABEL: @caller3
 ;CHECK-LABEL: Top.split:
 ;CHECK: call void @dummy4()
 ;CHECK-LABEL: NextCond.split:
@@ -76,7 +108,7 @@
 ;CheCK-LABEL: CallSiteBB:
 ;CHECK: %phi.call = phi i1 [ true, %NextCond.split ], [ false, %Top.split ]
 ;CHECK: call void @foo(i1 %phi.call)
-define void @caller2(i1 %c, %struct.bitmap* %a_elt, %struct.bitmap* %b_elt, %struct.bitmap* %c_elt) {
+define void @caller3(i1 %c, %struct.bitmap* %a_elt, %struct.bitmap* %b_elt, %struct.bitmap* %c_elt) {
 entry:
   br label %Top