[RISCV] Use uint64_t operations instead of APInt operations. NFC

We already know the type is i64 here. Just extract the uint64_t.

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -15515,7 +15515,7 @@ static SDValue performSRACombine(SDNode *N, SelectionDAG &DAG,
       return SDValue();
 
     // AddC needs to have at least 32 trailing zeros.
-    if (AddC->getAPIntValue().countr_zero() < 32)
+    if (llvm::countr_zero(AddC->getZExtValue()) < 32)
       return SDValue();
 
     // All users should be a shift by constant less than or equal to 32. This
@@ -15553,7 +15553,7 @@ static SDValue performSRACombine(SDNode *N, SelectionDAG &DAG,
   // constant.
   if (AddC) {
     SDValue ShiftedAddC =
-        DAG.getConstant(AddC->getAPIntValue().lshr(32), DL, MVT::i64);
+        DAG.getConstant(AddC->getZExtValue() >> 32, DL, MVT::i64);
     if (IsAdd)
       In = DAG.getNode(ISD::ADD, DL, MVT::i64, In, ShiftedAddC);
     else