[llvm] [LV][NFC] Remove remaining uses of undef in tests (PR #169357)

[David Sherwood via llvm-commits]

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@@ -13,7 +13,7 @@ bb:
   br label %bb2
 
 bb2:                                              ; preds = %bb2, %bb
-  %tmp4 = icmp slt i32 undef, 0
+  %tmp4 = icmp slt i32 poison, 0
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david-arm wrote:

git blame is completely messed up because many old loop vectoriser tests always point back to this commit cee313d288a4faf0355d76fb6e0e927e211d08a5. However, using the command `git blame a86343512845c9c1fdbac865fea88aa5fce7142a^ ../llvm/test/Transforms/LoopVectorize/X86/pr39160.ll` I can see it was introduced by https://reviews.llvm.org/D52881. I'll see if I can either rewrite it to be more useful or perhaps just delete the test entirely if it's no longer of any value?

https://github.com/llvm/llvm-project/pull/169357