[VP] Add method for looking up functional intrinsic ID for VP. NFC (#66190)

This adds a helper method to get the ID of the functionally equivalent
intrinsic, similar to the existing getFunctionalOpcodeForVP and
getConstrainedIntrinsicIDForVP methods.

Not sure if it's notable or not, but I can't find any existing uses of
VP_PROPERTY_FUNCTIONAL_INTRINSIC?

It could potentially be used in #65706 to scalarize VP intrinsics.

Author: lukel97

llvm/include/llvm/IR/IntrinsicInst.h

@@ -596,6 +596,11 @@ class VPIntrinsic : public IntrinsicInst {
     return getFunctionalOpcodeForVP(getIntrinsicID());
   }
 
+  // Equivalent non-predicated intrinsic ID
+  std::optional<unsigned> getFunctionalIntrinsicID() const {
+    return getFunctionalIntrinsicIDForVP(getIntrinsicID());
+  }
+
   // Equivalent non-predicated constrained ID
   std::optional<unsigned> getConstrainedIntrinsicID() const {
     return getConstrainedIntrinsicIDForVP(getIntrinsicID());
@@ -604,8 +609,12 @@ class VPIntrinsic : public IntrinsicInst {
   // Equivalent non-predicated opcode
   static std::optional<unsigned> getFunctionalOpcodeForVP(Intrinsic::ID ID);
 
+  // Equivalent non-predicated intrinsic ID
+  static std::optional<Intrinsic::ID>
+  getFunctionalIntrinsicIDForVP(Intrinsic::ID ID);
+
   // Equivalent non-predicated constrained ID
-  static std::optional<unsigned>
+  static std::optional<Intrinsic::ID>
   getConstrainedIntrinsicIDForVP(Intrinsic::ID ID);
 };
 

llvm/lib/IR/IntrinsicInst.cpp

@@ -529,8 +529,22 @@ VPIntrinsic::getFunctionalOpcodeForVP(Intrinsic::ID ID) {
   return std::nullopt;
 }
 
+// Equivalent non-predicated intrinsic
+std::optional<Intrinsic::ID>
+VPIntrinsic::getFunctionalIntrinsicIDForVP(Intrinsic::ID ID) {
+  switch (ID) {
+  default:
+    break;
+#define BEGIN_REGISTER_VP_INTRINSIC(VPID, ...) case Intrinsic::VPID:
+#define VP_PROPERTY_FUNCTIONAL_INTRINSIC(INTRIN) return Intrinsic::INTRIN;
+#define END_REGISTER_VP_INTRINSIC(VPID) break;
+#include "llvm/IR/VPIntrinsics.def"
+  }
+  return std::nullopt;
+}
+
 // Equivalent non-predicated constrained intrinsic
-std::optional<unsigned>
+std::optional<Intrinsic::ID>
 VPIntrinsic::getConstrainedIntrinsicIDForVP(Intrinsic::ID ID) {
   switch (ID) {
   default: