[llvm] [VP] Refactor VectorBuilder to avoid layering violation. NFC (PR #99276)

[Mel Chen via llvm-commits]

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@@ -367,6 +367,59 @@ TEST_F(VPIntrinsicTest, IntrinsicIDRoundTrip) {
   ASSERT_NE(FullTripCounts, 0u);
 }
 
+/// Check that going from intrinsic to VP intrinsic and back results in the same
+/// intrinsic.
+TEST_F(VPIntrinsicTest, IntrinsicToVPRoundTrip) {
+  unsigned FullTripCounts = 0;
+  Intrinsic::ID IntrinsicID = Intrinsic::not_intrinsic + 1;
+  for (; IntrinsicID < Intrinsic::num_intrinsics; IntrinsicID++) {
+    Intrinsic::ID VPID = VPIntrinsic::getForIntrinsic(IntrinsicID);
+    // No equivalent VP intrinsic available.
+    if (VPID == Intrinsic::not_intrinsic)
+      continue;
+
+    // Return itself if passed intrinsic ID is VP intrinsic.
+    if (VPIntrinsic::isVPIntrinsic(IntrinsicID)) {
+      ASSERT_EQ(IntrinsicID, VPID);
+      continue;
+    }
+
+    std::optional<Intrinsic::ID> RoundTripIntrinsicID =
+        VPIntrinsic::getFunctionalIntrinsicIDForVP(VPID);
+    // No equivalent non-predicated intrinsic available.
+    if (!RoundTripIntrinsicID)
+      continue;
+
+    ASSERT_EQ(*RoundTripIntrinsicID, IntrinsicID);
+    ++FullTripCounts;
+  }
+  ASSERT_NE(FullTripCounts, 0u);
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Mel-Chen wrote:

9f8748efca1708183f06bc469c03b6661f22c93e
There are two ways to improve this:
1. If we only need to check whether at least one full trip is completed, boolean is good enough.
2. Perform a detailed check of the number of full trips executed. Currently, there will be a total of 54 full trips.

For now, I will adopt the first way. 
If it needs to be changed to the second way, I have a question: Is there a simple way, besides using
```#define VP_PROPERTY_FUNCTIONAL_INTRINSIC(INTRIN) FullTripCountsAns++;```, to obtain the total number of corresponding equivalent non-VP intrinsics in VPIntrinsic?

https://github.com/llvm/llvm-project/pull/99276