[NativeAOT-LLVM] Create throw helper blocks on-demand in codegen

There are a number of advantages: 1) Simpler code - throw helper blocks are very special w.r.t. flowgraph handling 2) Less coupling with upstream code (SCK_NULLREF_EXCPN and related deleted). 3) Smaller LLVM.

Unfortunately, LLVM, as it turns out, is quite sensitive to block order, so we get the following diffs:

Summary of Code Size diffs:
(Lower is better)

Total bytes of base: 3286670
Total bytes of diff: 3288259
Total bytes of delta: 1589 (0.05% % of base)
Average relative delta: 5.19%
    diff is a regression
    average relative diff is a regression

Top method regressions (percentages):
         127 (153.01% of base) : 1150.dasm - S_P_TypeLoader_Internal_TypeSystem_CanonType__GetHashCode
         127 (153.01% of base) : 1148.dasm - S_P_TypeLoader_Internal_TypeSystem_UniversalCanonType__GetHashCode
         127 (138.04% of base) : 1149.dasm - S_P_TypeLoader_Internal_TypeSystem_CanonType__get_BaseType
         144 (91.14% of base) : 1005.dasm - HelloWasm_Program__ldindTest
         218 (85.49% of base) : 1116.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_EETypeCreator__GetInstanceGCDescSize
         272 (85.27% of base) : 1004.dasm - HelloWasm_Program_MixedArgFuncClass__MixedArgFunc
         144 (79.56% of base) : 1042.dasm - HelloWasm_Program___TestVirtualUnwindStackNoPopOnThrow_g__TestVirtualUnwindStackNoPopOnThrow_NotInTryCatch_229_0
         124 (79.49% of base) : 1035.dasm - HelloWasm_Program___TestVirtualUnwindStackPopSelfOnNestedUnwindingFault_g__TestVirtualUnwindStackPopSelfOnNestedUnwindingFault_Faults_237_0
         120 (68.57% of base) : 1175.dasm - S_P_CoreLib_Internal_Metadata_NativeFormat_MdBinaryReader__Read_18
          41 (50.00% of base) : 1061.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_GenericDictionaryCell_InterfaceCallCell__Create
         126 (43.45% of base) : 1126.dasm - S_P_TypeLoader_Internal_NativeFormat_NativeParser__GetParserForBagElementKind
          86 (43.43% of base) : 1098.dasm - S_P_TypeLoader_Internal_Runtime_MethodTable__get_GenericVariance
          58 (42.65% of base) : 1044.dasm - HelloWasm_Program___TestVirtualUnwindStackPopOnThrow_g__TestVirtualUnwindStackPopOnThrow_NotInTry_228_0
         104 (38.38% of base) : 1028.dasm - S_P_Reflection_Execution_Internal_Reflection_Execution_FieldAccessors_PointerTypeFieldAccessorForStaticFields__GetFieldBypassCctor
         141 (29.81% of base) : 1117.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_EETypeCreator__CreateInstanceGCDesc
         135 (26.01% of base) : 1141.dasm - S_P_TypeLoader_Internal_TypeSystem_NoMetadata_NoMetadataType__get_BaseType
          40 (24.84% of base) : 1059.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_GenericDictionaryCell_ThreadStaticIndexCell__Create
          37 (21.89% of base) : 1060.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_GenericDictionaryCell_FieldLdTokenCell__Create
         201 (19.76% of base) : 1128.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_TypeBuilderState__get_InstanceGCLayout
          30 (18.18% of base) : 1157.dasm - HelloWasm_Program__TestUnsignedLongAddOvf

Top method improvements (percentages):
         -55 (-67.90% of base) : 1124.dasm - S_P_TypeLoader_Internal_TypeSystem_TypeSystemContext_ArrayTypeKey_ArrayTypeKeyHashtable__GetKeyHashCode
         -93 (-61.18% of base) : 1026.dasm - HelloWasm_Program__TestLclVarAddr
        -120 (-40.13% of base) : 1201.dasm - S_P_CoreLib_Internal_Metadata_NativeFormat_MdBinaryReader__Read_24
         -88 (-36.36% of base) : 1027.dasm - HelloWasm_Program__TestJitUseStruct
        -110 (-35.95% of base) : 1114.dasm - S_P_CoreLib_Internal_Reflection_Core_Execution_ExecutionDomain__GetNamedTypeForHandle
         -45 (-32.37% of base) : 1123.dasm - S_P_TypeLoader_Internal_TypeSystem_TypeSystemContext_ArrayTypeKey_ArrayTypeKeyHashtable__GetValueHashCode
         -81 (-25.00% of base) : 1078.dasm - S_P_CoreLib_System_Globalization_DateTimeFormatInfo__PMDesignatorTChar<Char>
        -422 (-23.90% of base) : 1125.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_NativeLayoutInterfacesAlgorithm__ComputeRuntimeInterfaces
         -54 (-22.31% of base) : 1089.dasm - S_P_CoreLib_System_IO_RandomAccess__ValidateInput
        -135 (-20.96% of base) : 1127.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_NoMetadataRuntimeInterfacesAlgorithm__ComputeRuntimeInterfaces
        -126 (-17.12% of base) : 1093.dasm - S_P_CoreLib_Internal_Metadata_NativeFormat_MetadataReader__GetNamespaceDefinition
        -116 (-16.67% of base) : 1112.dasm - S_P_CoreLib_Internal_TypeSystem_LockFreeReaderHashtable_2<System___Canon__System___Canon>__TryGetValue
        -115 (-14.82% of base) : 1118.dasm - S_P_CoreLib_Internal_TypeSystem_LockFreeReaderHashtable_2<System___Canon__System___Canon>__Expand
         -31 (-13.48% of base) : 1023.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_TypeBuilder__FinishBaseTypeAndDictionaries
        -207 (-11.35% of base) : 1074.dasm - S_P_TypeLoader_Internal_Runtime_TypeLoader_TypeLoaderEnvironment__GVMLookupForSlotWorker
        -114 (-9.28% of base) : 1119.dasm - S_P_CoreLib_Internal_TypeSystem_LockFreeReaderHashtable_2<System___Canon__System___Canon>__TryAddOrGetExisting
         -70 (-6.42% of base) : 1122.dasm - S_P_TypeLoader_Internal_TypeSystem_TypeSystemContext___ctor_0
         -15 (-2.79% of base) : 1121.dasm - S_P_TypeLoader_Internal_TypeSystem_TypeSystemContext__get_LoadFactor
         -10 (-2.58% of base) : 1172.dasm - HelloWasm_Program___TestDeepContainedNestedDispatchIntraFrame_g__TestDeepContainedNestedDispatchSingleFrame_TrySix_243_6
          -1 (-2.56% of base) : 1030.dasm - HelloWasm_Program__DoNotThrowException

204 total methods with Code Size differences (101 improved, 103 regressed)

Most are inlining noise, but in some cases we get worse/better codegen due to the new order. Replicating the old older would be complex, so I opted for simpler code.

dotnet / runtimelab

[NativeAOT-LLVM] Create throw helper blocks on-demand in codegen #2446