adding edge case test

Author: joaosaffran

llvm/test/CodeGen/DirectX/rootsignature-validation-appending-limits.ll

@@ -0,0 +1,16 @@
+; RUN: opt -S -passes='dxil-post-optimization-validation' -mtriple=dxil-pc-shadermodel6.6-compute %s 2>&1 | FileCheck %s
+; This is correct according to DXC: https://hlsl.godbolt.org/z/KPG5o74KE
+; CHECK-NOT: error:
+
+define void @CSMain() "hlsl.shader"="compute" {
+entry:
+  ret void
+}
+
+!dx.rootsignatures = !{!0}
+
+!0 = !{ptr @CSMain, !1, i32 2}
+!1 = !{!3}
+!3 = !{!"DescriptorTable", i32 0, !4, !5}
+!4 = !{!"UAV", i32 1, i32 1, i32 0, i32 4294967294, i32 0}
+!5 = !{!"UAV", i32 1, i32 0, i32 0, i32 -1, i32 0}