[llvm] [AMDGPU] More accurately account for AVGPR pressure (PR #150711)

[Lucas Ramirez via llvm-commits]

================
@@ -99,20 +99,22 @@ void GCNRegPressure::inc(unsigned Reg,
 bool GCNRegPressure::less(const MachineFunction &MF, const GCNRegPressure &O,
                           unsigned MaxOccupancy) const {
   const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
+  unsigned ArchVGPRThreshold = ST.getMaxNumVectorRegs(MF.getFunction()).first;
----------------
lucas-rami wrote:

Would it make sense to make this a class member to avoid passing it every time we call `getVGPRNum`/`getAGPRNum`? It seems to always have the value `ST.getMaxNumVectorRegs(MF.getFunction()).first` which should not change throughout the `MF`'s lifetime.

https://github.com/llvm/llvm-project/pull/150711