[PowerPC] Add guard in LowerSELECT_CC for ppcf128

[tingwang]

Summary

LowerSELECT_CC can be used to lower intrinsics for example __builtin_max. In the long double case, we need to add this check so that ppcf128 does not wrongly pickup PPCISD::XSMAXC.

[lkail]

Please also add tests.

[tingwang]

In D122462#3407313, @lkail wrote:

Please also add tests.

This does not affect existing tests. The case to show is __builtin_max which I'm still working on, and will coming out shortly. I'm not sure if we can forge a test case to show its effectiveness in current code base.

[tingwang]

Not required

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

SDValue PPCTargetLowering::LowerSELECT_CC(SDValue Op, SelectionDAG &DAG) const {
   if (!CmpVT.isFloatingPoint() || !TV.getValueType().isFloatingPoint() ||
       Subtarget.hasSPE())
     return Op;
 
   SDNodeFlags Flags = Op.getNode()->getFlags();
 
   // We have xsmaxc[dq]p/xsminc[dq]p which are OK to emit even in the
   // presence of infinities.
-  if (Subtarget.hasP9Vector() && LHS == TV && RHS == FV) {
+  if (Subtarget.hasP9Vector() && LHS == TV && RHS == FV &&
+      CmpVT != MVT::ppcf128) {
     switch (CC) {
     default:
       break;
     case ISD::SETOGT:
     case ISD::SETGT:
       return DAG.getNode(PPCISD::XSMAXC, dl, Op.getValueType(), LHS, RHS);
     case ISD::SETOLT:
     case ISD::SETLT: