[llvm] [LV] Mark functions in legacy cost model const (NFC) (PR #216282)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -2496,8 +2488,8 @@ uint64_t LoopVectorizationCostModel::getPredBlockCostDivisor(
     return 1;
 
   uint64_t HeaderFreq =
-      getBFI().getBlockFreq(TheLoop->getHeader()).getFrequency();
-  uint64_t BBFreq = getBFI().getBlockFreq(BB).getFrequency();
+      GetBFI().getBlockFreq(TheLoop->getHeader()).getFrequency();
----------------
artagnon wrote:

As I predicated, compile-time change is within [noise](https://llvm-compile-time-tracker.com/compare.php?from=93ebddedab9833af230754ab49f5b642a02f36e6&to=d25ef33d7ffdf1c4bffba3d1b89b6aed1b90d2f6&stat=instructions:u). I don't think we need to have micro-optimizations that have no impact, at the cost of trading of const'ness.

https://github.com/llvm/llvm-project/pull/216282