[VPlan] Assign custom opcodes to recipes not mapping to IR opcodes.

We can perform CSE on recipes that do not directly map to Instruction
opcodes. One example is VPVectorPointerRecipe. Currently this is handled
by supporting them in ::canHandle, but currently that means that we
return std::nullopt from getOpcodeOrIntrinsicID() for it. This currently
only works, because the only case we return std::nullopt and perform CSE
is VPVectorPointerRecipe. But that does not work if we support more such
recipes, like VPPredInstPHIRecipe
(#162110).

To fix this, return a custom opcode from getOpcodeOrIntrinsicID for
recipes like VPVectorPointerRecipe, using the VPDefID after all regular
instruction opcodes.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1064,6 +1064,7 @@ class LLVM_ABI_FOR_TEST VPInstruction : public VPRecipeWithIRFlags,
     ResumeForEpilogue,
     /// Returns the value for vscale.
     VScale,
+    OpsEnd = VScale,
   };
 
   /// Returns true if this VPInstruction generates scalar values for all lanes.

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1988,6 +1988,13 @@ struct VPCSEDenseMapInfo : public DenseMapInfo<VPSingleDefRecipe *> {
         .Case<VPWidenIntrinsicRecipe>([](auto *I) {
           return std::make_pair(true, I->getVectorIntrinsicID());
         })
+        .Case<VPVectorPointerRecipe>([](auto *I) {
+          // For recipes that do not directly map to LLVM IR instructions,
+          // assign opcodes after the last VPInstruction opcode (which is also
+          // after the last IR Instruction opcode), based on the VPDefID.
+          return std::make_pair(false,
+                                VPInstruction::OpsEnd + 1 + I->getVPDefID());
+        })
         .Default([](auto *) { return std::nullopt; });
   }
 
@@ -2011,12 +2018,9 @@ struct VPCSEDenseMapInfo : public DenseMapInfo<VPSingleDefRecipe *> {
   static bool canHandle(const VPSingleDefRecipe *Def) {
     // We can extend the list of handled recipes in the future,
     // provided we account for the data embedded in them while checking for
-    // equality or hashing. We assign VPVectorEndPointerRecipe the GEP opcode,
-    // as it is essentially a GEP with different semantics.
-    auto C = isa<VPVectorPointerRecipe>(Def)
-                 ? std::make_pair(false, Instruction::GetElementPtr)
-                 : getOpcodeOrIntrinsicID(Def);
+    // equality or hashing.
 
+    auto C = getOpcodeOrIntrinsicID(Def);
     // The issue with (Insert|Extract)Value is that the index of the
     // insert/extract is not a proper operand in LLVM IR, and hence also not in
     // VPlan.
@@ -2054,6 +2058,8 @@ struct VPCSEDenseMapInfo : public DenseMapInfo<VPSingleDefRecipe *> {
         vputils::isSingleScalar(L) != vputils::isSingleScalar(R) ||
         !equal(L->operands(), R->operands()))
       return false;
+    assert(getOpcodeOrIntrinsicID(L) && getOpcodeOrIntrinsicID(R) &&
+           "must have valid opcode info for both recipes");
     if (auto *LFlags = dyn_cast<VPRecipeWithIRFlags>(L))
       if (LFlags->hasPredicate() &&
           LFlags->getPredicate() !=