[llvm] [NFC ]Add a helper function isTailCall for getting libcall in SelectionDAG (PR #155256)

[zhijian lin via llvm-commits]

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@@ -9012,6 +9012,14 @@ static void checkAddrSpaceIsValidForLibcall(const TargetLowering *TLI,
   }
 }
 
+static bool isTailCall(const CallInst *CI, const SelectionDAG *SelDAG,
+                       bool IsLowerToLibCall) {
+  bool ReturnsFirstArg = CI && funcReturnsFirstArgOfCall(*CI);
+  return CI && CI->isTailCall() &&
+         isInTailCallPosition(*CI, SelDAG->getTarget(),
+                              ReturnsFirstArg && IsLowerToLibCall);
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diggerlin wrote:

thanks for explain to me in person, I add TODO comment as your suggestion.

https://github.com/llvm/llvm-project/pull/155256