[llvm] [AArch64][SVE] Implement demanded bits for @llvm.aarch64.sve.cntp (PR #168714)

[Matthew Devereau via llvm-commits]

================
@@ -19443,20 +19443,38 @@ AArch64TargetLowering::BuildSREMPow2(SDNode *N, const APInt &Divisor,
   return CSNeg;
 }
 
-static std::optional<unsigned> IsSVECntIntrinsic(SDValue S) {
+static bool IsSVECntIntrinsic(SDValue S) {
   switch(getIntrinsicID(S.getNode())) {
   default:
     break;
   case Intrinsic::aarch64_sve_cntb:
-    return 8;
   case Intrinsic::aarch64_sve_cnth:
-    return 16;
   case Intrinsic::aarch64_sve_cntw:
-    return 32;
   case Intrinsic::aarch64_sve_cntd:
-    return 64;
+  case Intrinsic::aarch64_sve_cntp:
+    return true;
+  }
+  return false;
+}
+
+// Returns the maximum (scalable) value that can be returned by an SVE count
+// intrinsic. The supported intrinsics are covered by IsSVECntIntrinsic.
+static ElementCount getMaxValueForSVECntIntrinsic(SDValue Op) {
+  Intrinsic::ID IID = getIntrinsicID(Op.getNode());
+  if (IID == Intrinsic::aarch64_sve_cntp)
+    return Op.getOperand(1).getValueType().getVectorElementCount();
+  switch (IID) {
+  case Intrinsic::aarch64_sve_cntd:
+    return ElementCount::getScalable(2);
+  case Intrinsic::aarch64_sve_cntw:
+    return ElementCount::getScalable(4);
+  case Intrinsic::aarch64_sve_cnth:
+    return ElementCount::getScalable(8);
+  case Intrinsic::aarch64_sve_cntb:
+    return ElementCount::getScalable(16);
+  default:
+    llvm_unreachable("unexpected intrininc");
----------------
MDevereau wrote:

```suggestion
    llvm_unreachable("Unexpected intrinsic");
```


https://github.com/llvm/llvm-project/pull/168714