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-or-phi.ll
===================================================================
--- test/Transforms/CallSiteSplitting/callsite-split-or-phi.ll
+++ test/Transforms/CallSiteSplitting/callsite-split-or-phi.ll
@@ -532,3 +532,64 @@
 
 declare void @dummy(i32*, i32)
 declare void @dummy2(i32, i32)
+declare void @dummy3(i32*, i32*, i32*, i32*, i32*, i32*)
+declare void @dummy4(i32*)
+
+define void @callee2(i32* %dst_elt, i32* %a_elt, i32* %b_elt, i1 %c) {
+entry:
+  %tobool = icmp ne i32* %a_elt, null
+  %tobool1 = icmp ne i32* %b_elt, null
+  %or.cond = and i1 %tobool, %tobool1
+  br i1 %or.cond, label %Cond, label %Big
+
+Cond:
+  %cmp = icmp eq i32*  %dst_elt, %a_elt
+  br i1 %cmp, label %Small, label %Big
+
+Small:
+  call void @dummy4(i32* %a_elt)
+  br label %End
+
+Big:
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  call void @dummy3(i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt, i32* %a_elt)
+  br label %End
+
+End:
+  ret void
+}
+
+; Make sure we remove the non-nullness on constant paramater.
+;
+;CHECK-LABEL: @caller2
+;CHECK-LABEL: Top1.split:
+;CHECK: call void @callee2(i32* inttoptr (i64 4643 to i32*), i32* inttoptr (i64 4643 to i32*), i32* %b_elt, i1 false)
+define void @caller2(i1 %c, i32* %a_elt, i32* %b_elt) {
+entry:
+  br label %Top0
+
+Top0:
+  %tobool1 = icmp eq i32* %a_elt, inttoptr (i64 4643 to  i32*) 
+  br i1 %tobool1, label %Top1, label %NextCond
+
+Top1:
+  %tobool2 = icmp ne i32* %a_elt, null
+  br i1 %tobool2, label %CallSiteBB, label %NextCond
+
+NextCond:
+  %cmp = icmp ne i32* %b_elt, null
+  br i1 %cmp, label %CallSiteBB, label %End
+
+CallSiteBB:
+  %p = phi i1 [0, %Top1], [%c, %NextCond]
+  call void @callee2(i32* %a_elt, i32* %a_elt, i32* %b_elt, i1 %p)
+  br label %End
+
+End:
+  ret void
+}