[TTI] Check type legalization of both src and result for fpto{u|s}i.sat. (#147657)

For the cast instructions such ass `fptoui.sat`, `fptosi.sat`, need to
check
both type of the source and the result type can be lowering legally. If
one of them is invalid, return invalid cost.

--
Fixes #142973.

---------

Co-authored-by: Craig Topper <craig.topper@sifive.com>

Author: ElvisWang123

llvm/include/llvm/CodeGen/BasicTTIImpl.h

@@ -2498,11 +2498,18 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
       ISD = ISD::UMULO;
       break;
     case Intrinsic::fptosi_sat:
-      ISD = ISD::FP_TO_SINT_SAT;
-      break;
-    case Intrinsic::fptoui_sat:
-      ISD = ISD::FP_TO_UINT_SAT;
+    case Intrinsic::fptoui_sat: {
+      std::pair<InstructionCost, MVT> SrcLT = getTypeLegalizationCost(Tys[0]);
+      std::pair<InstructionCost, MVT> RetLT = getTypeLegalizationCost(RetTy);
+
+      // For cast instructions, types are different between source and
+      // destination. Also need to check if the source type can be legalize.
+      if (!SrcLT.first.isValid() || !RetLT.first.isValid())
+        return InstructionCost::getInvalid();
+      ISD = IID == Intrinsic::fptosi_sat ? ISD::FP_TO_SINT_SAT
+                                         : ISD::FP_TO_UINT_SAT;
       break;
+    }
     case Intrinsic::ctpop:
       ISD = ISD::CTPOP;
       // In case of legalization use TCC_Expensive. This is cheaper than a