Eliminate target hook IsEligibleForTailCallOptimization.

Target independent isel should always pass along the "tail call" property. Change
target hook LowerCall's parameter "isTailCall" into a refernce. If the target
decides it's impossible to honor the tail call request, it should set isTailCall
to false to make target independent isel happy.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94626 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -4651,9 +4651,6 @@ SelectionDAGBuilder::visitIntrinsicCall(CallInst &I, unsigned Intrinsic) {
 /// between it and the return.
 ///
 /// This function only tests target-independent requirements.
-/// For target-dependent requirements, a target should override
-/// TargetLowering::IsEligibleForTailCallOptimization.
-///
 static bool
 isInTailCallPosition(const Instruction *I, Attributes CalleeRetAttr,
                      const TargetLowering &TLI) {
@@ -6204,12 +6201,6 @@ TargetLowering::LowerCallTo(SDValue Chain, const Type *RetTy,
     }
   }
 
-  // Check if target-dependent constraints permit a tail call here.
-  // Target-independent constraints should be checked by the caller.
-  if (isTailCall &&
-      !IsEligibleForTailCallOptimization(Callee, CallConv, isVarArg, Ins, DAG))
-    isTailCall = false;
-
   SmallVector<SDValue, 4> InVals;
   Chain = LowerCall(Chain, Callee, CallConv, isVarArg, isTailCall,
                     Outs, Ins, dl, DAG, InVals);