[llvm] [LV][NFC] Use APFloat class when printing out costs per lane (PR #201824)

[David Sherwood via llvm-commits]

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@@ -47,6 +47,14 @@ using VectorParts = SmallVector<Value *, 2>;
 #define LV_NAME "loop-vectorize"
 #define DEBUG_TYPE LV_NAME
 
+#if !defined(NDEBUG)
+// It is sometimes necessary to disable printing of metadata in tests in order
+// to avoid non-deterministic behaviour.
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david-arm wrote:

Even without any metadata on the input IR, vplan generates metadata in some cases and prints with what looks a pointer/hex value that changes every time you run the test. That makes it impossible to write CHECK lines in tests.

https://github.com/llvm/llvm-project/pull/201824