/// Extract call from statepoint, lower it and return pointer to the
/// call node. Also update NodeMap so that getValue(statepoint) will
/// reference lowered call result
static std::pair<SDValue, SDNode *> lowerCallFromStatepointLoweringInfo(
SelectionDAGBuilder::StatepointLoweringInfo &SI,
SelectionDAGBuilder &Builder, SmallVectorImpl<SDValue> &PendingExports) {
SDValue ReturnValue, CallEndVal;
std::tie(ReturnValue, CallEndVal) =
Builder.lowerInvokable(SI.CLI, SI.EHPadBB);
SDNode *CallEnd = CallEndVal.getNode();
// Get a call instruction from the call sequence chain. Tail calls are not
// allowed. The following code is essentially reverse engineering X86's
// LowerCallTo.
//
// We are expecting DAG to have the following form:
//
// ch = eh_label (only in case of invoke statepoint)
// ch, glue = callseq_start ch
// ch, glue = X86::Call ch, glue
// ch, glue = callseq_end ch, glue
// get_return_value ch, glue
//
// get_return_value can either be a sequence of CopyFromReg instructions
// to grab the return value from the return register(s), or it can be a LOAD
// to load a value returned by reference via a stack slot.
bool HasDef = !SI.CLI.RetTy->isVoidTy();
if (HasDef) {
if (CallEnd->getOpcode() == ISD::LOAD)
CallEnd = CallEnd->getOperand(0).getNode();
else
while (CallEnd->getOpcode() == ISD::CopyFromReg)
CallEnd = CallEnd->getOperand(0).getNode();
}
assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!");
return std::make_pair(ReturnValue, CallEnd->getOperand(0).getNode());
}
