[llvm] [X86][BreakFalseDeps] Using reverse order for undef register selection (PR #137569)

[Simon Pilgrim via llvm-commits]

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@@ -88,7 +90,8 @@ class RegisterClassInfo {
 
   /// runOnFunction - Prepare to answer questions about MF. This must be called
   /// before any other methods are used.
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RKSimon wrote:

Update description to explain Rev

https://github.com/llvm/llvm-project/pull/137569