[llvm] Do not use R12 for indirect tail calls with PACBTI (PR #82661)

[via llvm-commits]

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@@ -228,6 +228,10 @@ def DontGenExecuteOnly : Predicate<"!Subtarget->genExecuteOnly()">;
 def GenT1ExecuteOnly : Predicate<"Subtarget->genExecuteOnly() && "
                                  "Subtarget->isThumb1Only() && "
                                  "!Subtarget->hasV8MBaselineOps()">;
+let RecomputePerFunction = 1 in {
+  def TailCallNotR12 : Predicate<[{ MF->getInfo<ARMFunctionInfo>()->shouldSignReturnAddress(true) }]>;
+  def TailCall : Predicate<[{ !MF->getInfo<ARMFunctionInfo>()->shouldSignReturnAddress(true) }]>;
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ostannard wrote:

This name isn't very descriptive, it doesn't affect the presence of tail-calls, just one detail of them. How about `TailCallAnyReg`, or describe the condition instead of the effect, like `SignRetAddr` and `NoSignRetAddr`?

https://github.com/llvm/llvm-project/pull/82661