[llvm] [PowerPC] Spill non-volatile registers required for traceback table (PR #71115)

[Stefan Pintilie via llvm-commits]

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@@ -2741,6 +2743,66 @@ bool PPCFrameLowering::enableShrinkWrapping(const MachineFunction &MF) const {
   return !MF.getSubtarget<PPCSubtarget>().is32BitELFABI();
 }
 
+static bool isGPR(MCPhysReg Reg) { return Reg >= PPC::R0 && Reg <= PPC::R31; }
+static bool isG8R(MCPhysReg Reg) { return Reg >= PPC::X0 && Reg <= PPC::X31; }
+static bool isFPR(MCPhysReg Reg) { return Reg >= PPC::F0 && Reg <= PPC::F31; }
+static bool isVR(MCPhysReg Reg) { return Reg >= PPC::V0 && Reg <= PPC::V31; }
+
+void PPCFrameLowering::updateCalleeSaves(const MachineFunction &MF,
+                                         BitVector &SavedRegs) const {
+  // The AIX ABI uses traceback tables for EH which require that if callee-saved
+  // register N is used, all registers N-31 must be saved/restored.
+  // NOTE: The check for AIX is not actually what is relevant. Traceback tables
+  // on Linux have the same requirements. It is just that AIX is the only ABI
+  // for which we actually use traceback tables. If another ABI needs to be
+  // supported that also uses them, we can add a check such as
+  // Subtarget.usesTraceBackTables().
+  assert(Subtarget.isAIXABI() && "function only called for AIX");
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stefanp-ibm wrote:

nit:
Complete sentence for the error. 
"Function updateCalleeSaves should only be called for AIX."

https://github.com/llvm/llvm-project/pull/71115