[llvm] [NFC][AMDGPU] Compute always reserved registers once (PR #132006)

[Jay Foad via llvm-commits]

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@@ -680,6 +684,12 @@ BitVector SIRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   // Reserve null register - it shall never be allocated
   reserveRegisterTuples(Reserved, AMDGPU::SGPR_NULL64);
 
+  return this->AlwaysReservedRegs = Reserved;
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jayfoad wrote:

This copies the bitvector, right? Could avoid that with std::move or by making Reserved a reference to AlwaysReservedRegs in the first place.

https://github.com/llvm/llvm-project/pull/132006