[llvm] [PPC][AIX] Save/restore r31 when using base pointer (PR #100182)

[Chen Zheng via llvm-commits]

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@@ -2025,8 +2025,18 @@ void PPCFrameLowering::determineCalleeSaves(MachineFunction &MF,
   // code. Same goes for the base pointer and the PIC base register.
   if (needsFP(MF))
     SavedRegs.reset(isPPC64 ? PPC::X31 : PPC::R31);
-  if (RegInfo->hasBasePointer(MF))
+  if (RegInfo->hasBasePointer(MF)) {
     SavedRegs.reset(RegInfo->getBaseRegister(MF));
+    // On AIX, when BaseRegister(R30) is used, need to spill r31 too to match
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chenzheng1030 wrote:

nit: maybe it's good to make R30 and r31 be consistent, my bad : )

https://github.com/llvm/llvm-project/pull/100182