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dotnet / runtimelab

This repo is for experimentation and exploring new ideas that may or may not make it into the main dotnet/runtime repo.
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[NativeAOT-LLVM] Work around LLVM issues with null checks #2500

Closed SingleAccretion closed 5 months ago

SingleAccretion commented 5 months ago

It turns out that LLVM's fast lowering, FastISel, produces very bad debug code for most relops, except for one very specific form of x == 0. Use this form in null checking, and enable address mode lowering for a total of 6.4% wins in code size:

Summary of Code Size diffs:
(Lower is better)

Total bytes of base: 15594261
Total bytes of diff: 14596617
Total bytes of delta: -997644 (-6.40% % of base)
Average relative delta: -14.05%
    diff is an improvement
    average relative diff is an improvement

Top method regressions (percentages):
        7678 (79.19% of base) : 2694.dasm - S_P_CoreLib_System_Globalization_OrdinalCasing___cctor
         208 (22.46% of base) : 3459.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_Attributes
         100 (22.42% of base) : 3418.dasm - S_P_CoreLib_System_Reflection_Runtime_General_Helpers___cctor
          77 (19.90% of base) : 4624.dasm - S_P_CoreLib_System_TimeZoneInfo_AdjustmentRule__get_DaylightTransitionEnd
         218 (18.78% of base) : 5012.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_DeclaredPropertyHandles
         218 (18.78% of base) : 3520.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_DeclaredFieldHandles
         218 (18.78% of base) : 1703.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_DeclaredEventHandles
         218 (18.78% of base) : 4157.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_DeclaredMethodAndConstructorHandles
          67 (17.31% of base) : 3996.dasm - S_P_CoreLib_System_TimeZoneInfo_AdjustmentRule__get_DaylightTransitionStart
         178 (14.71% of base) : 2757.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_Name
         195 (13.50% of base) : 2760.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_IsGenericTypeDefinition
         157 (12.89% of base) : 5795.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__get_TrueCustomAttributes
         201 (12.14% of base) : 4060.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeNamedTypeInfo__GetGenericTypeDefinition
         172 (12.13% of base) : 6223.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeGenericParameterTypeInfo__get_Name
          64 (11.39% of base) : 3663.dasm - S_P_CoreLib_System_Reflection_Runtime_ParameterInfos_NativeFormat_NativeFormatMethodParameterInfo__get_Attributes
          64 (10.53% of base) : 6224.dasm - S_P_CoreLib_System_Reflection_Runtime_TypeInfos_NativeFormat_NativeFormatRuntimeGenericParameterTypeInfo__get_GenericParameterAttributes
          64 ( 9.60% of base) : 3662.dasm - S_P_CoreLib_System_Reflection_Runtime_ParameterInfos_NativeFormat_NativeFormatMethodParameterInfo__get_Name
          47 ( 8.82% of base) : 2435.dasm - S_P_CoreLib_System_Reflection_Runtime_FieldInfos_NativeFormat_NativeFormatRuntimeFieldInfo__get_ExplicitLayoutFieldOffsetData
          64 ( 8.64% of base) : 3714.dasm - S_P_CoreLib_System_Reflection_Runtime_ParameterInfos_NativeFormat_NativeFormatMethodParameterInfo__get_TrueCustomAttributes
          47 ( 8.42% of base) : 4236.dasm - S_P_CoreLib_System_Reflection_Runtime_FieldInfos_NativeFormat_NativeFormatRuntimeFieldInfo__get_Attributes

Top method improvements (percentages):
        -915 (-51.17% of base) : 4555.dasm - S_P_CoreLib_System_Globalization_CalendarData___ctor
        -641 (-47.66% of base) : 1879.dasm - S_P_CoreLib_System_Globalization_CultureData___ctor
       -1413 (-42.82% of base) : 1868.dasm - S_P_CoreLib_System_Globalization_NumberFormatInfo___ctor_0
       -1009 (-41.47% of base) : 1048.dasm - S_P_CoreLib_System_Text_StringBuilder__AssertInvariants
        -415 (-41.13% of base) : 1152.dasm - S_P_CoreLib_System_Text_StringBuilder___ctor_6
       -4145 (-41.08% of base) : 1880.dasm - S_P_CoreLib_System_Globalization_CultureData__CreateCultureWithInvariantData
        -333 (-40.56% of base) : 3095.dasm - S_P_CoreLib_System_Collections_Hashtable_HashtableEnumerator___ctor
        -575 (-40.18% of base) : 2316.dasm - S_P_TypeLoader_System_Collections_Generic_LowLevelDictionary_2_LowLevelDictEnumerator<System___Canon__System___Canon>__MoveNext
        -795 (-40.09% of base) : 1304.dasm - S_P_CoreLib_System_Text_EncoderReplacementFallbackBuffer__GetNextChar
        -795 (-40.09% of base) : 2108.dasm - S_P_CoreLib_System_Text_DecoderReplacementFallbackBuffer__GetNextChar
        -172 (-39.91% of base) : 6110.dasm - S_P_CoreLib_System_Text_EncoderReplacementFallbackBuffer__Reset
        -549 (-39.87% of base) : 2042.dasm - S_P_CoreLib_System_Resources_ResourceReader__Dispose_0
        -587 (-39.50% of base) : 3043.dasm - S_P_CoreLib_Internal_Reflection_Extensions_NonPortable_CustomAttributeSearcher_1__GetMatchingCustomAttributesIterator_d__2<System___Canon>__System_Collections_Generic_IEnumerable_System_Reflection_CustomAttributeData__GetEnumerator
        -507 (-39.27% of base) : 5356.dasm - S_P_CoreLib_System_Collections_Generic_LowLevelList_1<IntPtr>__Add
        -499 (-39.23% of base) : 6342.dasm - S_P_TypeLoader_System_Collections_Generic_LowLevelList_1<Bool>__Add
        -117 (-38.87% of base) : 2983.dasm - S_P_CoreLib_System_IO_Strategies_BufferedFileStreamStrategy__Dispose$F1_Finally
        -129 (-38.74% of base) : 1153.dasm - S_P_CoreLib_System_Text_StringBuilder__get_Capacity
       -1156 (-38.70% of base) : 3097.dasm - S_P_CoreLib_System_Collections_Hashtable_HashtableEnumerator__MoveNext
        -517 (-38.70% of base) : 6269.dasm - S_P_CoreLib_System_Collections_Generic_LowLevelList_1<S_P_CoreLib_System_Reflection_Runtime_General_QTypeDefRefOrSpec>__Add
        -951 (-38.69% of base) : 1619.dasm - S_P_CoreLib_System_Version__CompareTo_0

5459 total methods with Code Size differences (5420 improved, 39 regressed)

I looked briefly at the regressions, they look like some other intersection of LLVM issues with our codegen (particularly #2351).

Upstream issue: https://github.com/llvm/llvm-project/issues/80053.

SingleAccretion commented 5 months ago

@dotnet/nativeaot-llvm