[llvm] [CodeGen] Refactor `determineCalleeSaves`. (PR #166763)

[Mikhail Gudim via llvm-commits]

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@@ -390,9 +390,38 @@ class LLVM_ABI TargetFrameLowering {
   /// This method should not be called by any passes outside of PEI, because
   /// it may change state passed in by \p MF and \p RS. The preferred
   /// interface outside PEI is getCalleeSaves.
+  // LLVM_DEPRECATED("Use determinePrologCalleeSaves instead",
+  //                 "determinePrologCalleeSaves")
   virtual void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                                     RegScavenger *RS = nullptr) const;
 
+  /// Return the list of registers which must be preserved by the function: the
+  /// value on exit must be the same as the value on entry. A register from this
+  /// list does not need to be saved / reloaded if the function did not use it.
+  const MCPhysReg *getMustPreserveRegisters(const MachineFunction &MF) const;
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mgudim wrote:

This function returns the result of `getCalleeSavedRegs()` or `getIPRACSRegs(&MF)` both return just a pointer. It will be  hard to change `getCalleeSavedRegs` because every target implements it. I could of course just copy the result into a vector and return it, but do we want that?

https://github.com/llvm/llvm-project/pull/166763