diff --git a/lib/Target/X86/README-UNIMPLEMENTED.txt b/lib/Target/X86/README-UNIMPLEMENTED.txt
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+//===---------------------------------------------------------------------===//
+// Testcases that crash the X86 backend because they aren't implemented
+//===---------------------------------------------------------------------===//
+
+These are cases we know the X86 backend doesn't handle.  Patches are welcome
+and appreciated, because no one has signed up to implemented these yet.
+Implementing these would allow elimination of the corresponding intrinsics,
+which would be great.
+
+1) vector shifts
+2) vector comparisons
+3) vector fp<->int comparisons: PR2683, PR2684, PR2685, PR2686, PR2688
+
+