[PowerPC] Fix PR16556 (handle undef ppcf128 in LowerFP_TO_INT).

PPCTargetLowering::LowerFP_TO_INT() expects its source operand to be
either an f32 or f64, but this is not checked.  A long double
(ppcf128) operand will normally be custom-lowered to a conversion to
f64 in this context.  However, this isn't the case for an UNDEF node.

This patch recognizes a ppcf128 as a legal source operand for
FP_TO_INT only if it's an undef, in which case it creates an undef of
the target type.

At some point we might want to do a wholesale custom lowering of
ISD::UNDEF when the type is ppcf128, but it's not really clear that's
a great idea, and probably more work than it's worth for a situation
that only arises in the case of a programming error.  At this point I
think simple is best.

The test case comes from PR16556, and is a crash-test only.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185821 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCISelLowering.cpp

@@ -4685,6 +4685,15 @@ SDValue PPCTargetLowering::LowerFP_TO_INT(SDValue Op, SelectionDAG &DAG,
                                            SDLoc dl) const {
   assert(Op.getOperand(0).getValueType().isFloatingPoint());
   SDValue Src = Op.getOperand(0);
+
+  // If we have a long double here, it must be that we have an undef of
+  // that type.  In this case return an undef of the target type.
+  if (Src.getValueType() == MVT::ppcf128) {
+    assert(Src.getOpcode() == ISD::UNDEF && "Unhandled ppcf128!");
+    return DAG.getNode(ISD::UNDEF, dl,
+                       Op.getValueType().getSimpleVT().SimpleTy);
+  }
+
   if (Src.getValueType() == MVT::f32)
     Src = DAG.getNode(ISD::FP_EXTEND, dl, MVT::f64, Src);