[llvm] [RISCV][TTI] Add instruction cost for vp.select. (PR #109381)

[Elvis Wang via llvm-commits]

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@@ -1065,6 +1065,13 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
         *FOp, ICA.getArgTypes()[0], UI->getPointerAlignment(),
         UI->getOperand(1)->getType()->getPointerAddressSpace(), CostKind);
   }
+  case Intrinsic::vp_select: {
+    Intrinsic::ID IID = ICA.getID();
+    std::optional<unsigned> FOp = VPIntrinsic::getFunctionalOpcodeForVP(IID);
+    assert(FOp.has_value());
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ElvisWang123 wrote:

The `VPIntrinsic::getFunctionalOpcodeForVP()` will return an optional with value when the VPIntrinsic has corresponding instruction opcode.
We can find the mapping table in the `llvm/include/llvm/IR/VPIntrinsics.def` which contains a macro called `VP_PROPERTY_FUNCTIONAL_OPC`. 
Any query of the opcode for VPIntrinsics with `VP_PROPERTY_FUNCTIONAL_OPC` will not return  `std::nullopt`.  [Source](https://llvm.org/doxygen/IntrinsicInst_8cpp_source.html#l00519)


In this case, the vp_select contains the `VP_PROPERTY_FUNCTIONAL_OPC(Select)` attribute so we can assert that the `FOp` has value. [Source](https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/IR/VPIntrinsics.def#L720C1-L720C27)

https://github.com/llvm/llvm-project/pull/109381