[llvm] [DAG] Support saturated truncate (PR #99418)

[Simon Pilgrim via llvm-commits]

================
@@ -1908,6 +1909,8 @@ SDValue DAGCombiner::visit(SDNode *N) {
   case ISD::ZERO_EXTEND_VECTOR_INREG:
   case ISD::ANY_EXTEND_VECTOR_INREG: return visitEXTEND_VECTOR_INREG(N);
   case ISD::TRUNCATE:           return visitTRUNCATE(N);
+  case ISD::TRUNCATE_SSAT_U:
+  case ISD::TRUNCATE_USAT_U:    return visitTRUNCATE_USAT(N);
----------------
RKSimon wrote:

No, we can generalize it later if the need arises - but we need to confirm if we should be handling the TRUNCATE_SSAT_U  case or not (do we have test coverage?)

https://github.com/llvm/llvm-project/pull/99418