[PATCH] D110218: [CodeGen][NFC] Add comment to `getCSRFirstUseCost`

[Kai Luo via Phabricator via llvm-commits]

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>From usage in `RAGreedy::initializeCSRCost` and `AArch64RegisterInfo::getCSRFirstUseCost`, this value is set assuming `MachineBlockFrequencyInfo::getEntryFreq()` is 1<<14. Add comment to clarify it so that other target can override it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110218

Files:
  llvm/include/llvm/CodeGen/TargetRegisterInfo.h


Index: llvm/include/llvm/CodeGen/TargetRegisterInfo.h
===================================================================
--- llvm/include/llvm/CodeGen/TargetRegisterInfo.h
+++ llvm/include/llvm/CodeGen/TargetRegisterInfo.h
@@ -875,7 +875,8 @@
 
   /// Allow the target to override the cost of using a callee-saved register for
   /// the first time. Default value of 0 means we will use a callee-saved
-  /// register if it is available.
+  /// register if it is available. This value is set assuming entry block
+  /// frequency is 1<<14.
   virtual unsigned getCSRFirstUseCost() const { return 0; }
 
   /// Returns true if the target requires (and can make use of) the register


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