diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3194,7 +3194,8 @@
                                            ->getType()
                                            ->getPointerAddressSpace()))) {
         Value *V = CS->getArgOperand(Idx);
-
+        if (isa<UndefValue>(*V))
+          continue;
         Builder.SetInsertPoint(I->getParent(), I->getIterator());
         Builder.CreateAssumption(Builder.CreateIsNotNull(V));
       }
diff --git a/llvm/test/Transforms/InstCombine/assume-replacing-call.ll b/llvm/test/Transforms/InstCombine/assume-replacing-call.ll
--- a/llvm/test/Transforms/InstCombine/assume-replacing-call.ll
+++ b/llvm/test/Transforms/InstCombine/assume-replacing-call.ll
@@ -183,6 +183,30 @@
   ret i32 %retval.0
 }
 
+define i64 @test_sink_undef(i1 %c, i64 %x) {
+; Check that we don't insert a nonnull assumption for undef.
+; CHECK-LABEL: @test_sink_undef(
+; CHECK-NEXT: entry:
+; CHECK-NOT:    @llvm.assume(
+; CHECK:        br i1 %c, label %ctrue, label %cend
+; CHECK:      ctrue:
+; CHECK-NEXT:   %foo = call i64 @func_test_nonnull(i8* undef)
+; CHECK-NEXT:   br label %cend
+; CHECK:      cend:
+; CHECK-NEXT:   %retval = phi i64 [ %x, %entry ], [ %foo, %ctrue ]
+; CHECK-NEXT:   ret i64 %retval
+entry:
+  %foo = call i64 @func_test_nonnull(i8* undef) #2
+  br i1 %c, label %ctrue, label %cend
+
+ctrue:
+  br label %cend
+
+cend:
+  %retval = phi i64 [%x, %entry], [%foo, %ctrue]
+  ret i64 %retval
+}
+
 declare i64 @func_test(i8* %0) #1
 
 declare i64 @func_test_nonnull(i8* nonnull %0) #3