[llvm] [clang] [SPARC] Support reserving arbitrary general purpose registers (PR #74927)

[Sergei Barannikov via cfe-commits]

================
@@ -98,9 +96,34 @@ BitVector SparcRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   for (unsigned n = 0; n < 31; n++)
     Reserved.set(SP::ASR1 + n);
 
+  for (size_t i = 0; i < SP::IntRegsRegClass.getNumRegs() / 4; ++i) {
+    // Mark both single register and register pairs.
+    if (MF.getSubtarget<SparcSubtarget>().isGRegisterReserved(i)) {
+      Reserved.set(SP::G0 + i);
+      Reserved.set(SP::G0_G1 + i / 2);
+    }
----------------
s-barannikov wrote:

```suggestion
    if (MF.getSubtarget<SparcSubtarget>().isGRegisterReserved(i))
      markSuperRegs(Reserved, SP::G0 + i);
```

https://github.com/llvm/llvm-project/pull/74927