Improve SequenceEqual for constant lengths unrolling

[EgorBo]

Slightly improve MemoryExtensions.SequenceEqual shape to expose more "constant length" cases for unrolling. It's a JIT phase ordering issue, in theory, if we run VN again after Assert prop we'll do the same in JIT, unfortunately, JIT's logic to run some phases more than once is currently broken.

After this PR, e.g. TryGetFloatingPointConstant is fully unrolled (all three SequenceEqual in it)

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Issue Details

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Slightly improve MemoryExtensions.SequenceEqual shape to expose more "constant length" cases for unrolling. It's a JIT phase ordering issue, in theory, if we run VN again after Assert prop we'll do the same in JIT, unfortunately, JIT's logic to run some phases more than once is currently broken.

After this PR, e.g. TryGetFloatingPointConstant is fully unrolled (all three SequenceEqual in it)

Author:	EgorBo
Assignees:	-
Labels:	area-System.Memory
Milestone:	-

[xtqqczze]

@EgorBo In theory, the length in (nuint)span.Length should be recognized as never negative, and the sign-extension elided, but doesn't appear to be the case (at least in R2R), see https://csharp.godbolt.org/z/14oW68fqz.

[EgorBo]

@xtqqczze thanks for suggestion but in this case I'm interesting in making SequenceEqual more unrolling friendly since some JIT optimizations are a bit too fragile (to be fixed). So the changes you suggested make sense but they brake that shape.

Current diffs:

Total bytes of base: 58409192
Total bytes of diff: 58409396
Total bytes of delta: 204 (0.00 % of base)
Total relative delta: NaN
    diff is a regression.
    relative diff is a regression.


Total byte diff includes -103 bytes from reconciling methods
        Base had    1 unique methods,      103 unique bytes
        Diff had    0 unique methods,        0 unique bytes

Top file regressions (bytes):
         150 : System.Security.Cryptography.Pkcs.dasm (0.03% of base)
         112 : System.Security.Cryptography.dasm (0.01% of base)
          51 : System.Text.Json.dasm (0.00% of base)
          15 : System.Net.Http.dasm (0.00% of base)
           6 : System.Diagnostics.Process.dasm (0.01% of base)
           6 : System.Net.Security.dasm (0.00% of base)
           6 : System.Security.AccessControl.dasm (0.01% of base)
           3 : System.Text.RegularExpressions.dasm (0.00% of base)
           3 : System.Security.Cryptography.Xml.dasm (0.00% of base)
           1 : System.Private.Xml.dasm (0.00% of base)

Top file improvements (bytes):
        -103 : Microsoft.CodeAnalysis.dasm (-0.01% of base)
         -28 : System.Reflection.MetadataLoadContext.dasm (-0.01% of base)
          -7 : Microsoft.Extensions.Primitives.dasm (-0.03% of base)
          -7 : System.Private.CoreLib.dasm (-0.00% of base)
          -4 : System.Formats.Asn1.dasm (-0.00% of base)

15 total files with Code Size differences (5 improved, 10 regressed), 261 unchanged.

Top method regressions (bytes):
          47 ( 3.17% of base) : System.Security.Cryptography.Pkcs.dasm - System.Security.Cryptography.Asn1.PssParamsAsn:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          47 ( 3.16% of base) : System.Security.Cryptography.dasm - System.Security.Cryptography.Asn1.PssParamsAsn:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          28 ( 2.60% of base) : System.Security.Cryptography.Pkcs.dasm - System.Security.Cryptography.Asn1.OaepParamsAsn:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          21 ( 2.03% of base) : System.Security.Cryptography.dasm - Internal.Cryptography.Helpers:AreSamePublicECParameters(System.Security.Cryptography.ECParameters,System.Security.Cryptography.ECParameters):bool
          16 ( 0.64% of base) : System.Security.Cryptography.dasm - System.Security.Cryptography.X509Certificates.Asn1.TbsCertificateAsn:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          16 ( 1.64% of base) : System.Security.Cryptography.dasm - System.Security.Cryptography.X509Certificates.DSACertificateExtensions:CopyWithPrivateKey(System.Security.Cryptography.X509Certificates.X509Certificate2,System.Security.Cryptography.DSA):System.Security.Cryptography.X509Certificates.X509Certificate2
          15 ( 1.94% of base) : System.Net.Http.dasm - System.Net.Http.Http2Connection+Http2Stream:OnHeader(System.ReadOnlySpan`1[ubyte],System.ReadOnlySpan`1[ubyte]):this
          12 ( 3.50% of base) : System.Security.Cryptography.Pkcs.dasm - System.Security.Cryptography.Asn1.Pbkdf2Params:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          12 ( 2.32% of base) : System.Security.Cryptography.Pkcs.dasm - System.Security.Cryptography.Pkcs.Asn1.EssCertIdV2:Encode(System.Formats.Asn1.AsnWriter,System.Formats.Asn1.Asn1Tag):this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[double]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[int]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[long]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[short]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[System.__Canon]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this
          12 ( 0.48% of base) : System.Text.Json.dasm - System.Text.Json.Serialization.Converters.ObjectWithParameterizedConstructorConverter`1[System.Nullable`1[int]]:TryLookupConstructorParameter(byref,byref,System.Text.Json.JsonSerializerOptions,byref):bool:this

Top method improvements (bytes):
        -103 (-100.00% of base) : Microsoft.CodeAnalysis.dasm - Microsoft.CodeAnalysis.SmallDictionary`2[System.__Canon,int]:RightComplex(Microsoft.CodeAnalysis.SmallDictionary`2+AvlNode[System.__Canon,int]):Microsoft.CodeAnalysis.SmallDictionary`2+AvlNode[System.__Canon,int] (1 base, 0 diff methods)
         -40 (-2.95% of base) : System.Text.Json.dasm - System.Text.Json.JsonDocument:TryGetNamedPropertyValue(int,int,System.ReadOnlySpan`1[ubyte],byref):bool:this
         -22 (-0.72% of base) : System.Reflection.MetadataLoadContext.dasm - System.Reflection.TypeLoading.Ecma.EcmaModule:GetTypeCoreNoCache(System.ReadOnlySpan`1[ubyte],System.ReadOnlySpan`1[ubyte],byref):System.Reflection.TypeLoading.RoDefinitionType:this
         -14 (-3.47% of base) : System.Text.Json.dasm - System.Text.Json.JsonReaderHelper:TryGetFloatingPointConstant(System.ReadOnlySpan`1[ubyte],byref):bool (2 methods)
          -8 (-0.58% of base) : System.Private.CoreLib.dasm - System.IO.Path:GetFullPath(System.String,System.String):System.String
          -7 (-3.95% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:Equals(System.String):bool:this
          -7 (-4.35% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:op_Equality(Microsoft.Extensions.Primitives.StringSegment,Microsoft.Extensions.Primitives.StringSegment):bool
          -7 (-4.05% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:op_Inequality(Microsoft.Extensions.Primitives.StringSegment,Microsoft.Extensions.Primitives.StringSegment):bool
          -7 (-2.11% of base) : System.Private.CoreLib.dasm - System.String:MakeSeparatorListAny(System.ReadOnlySpan`1[ushort],System.ReadOnlySpan`1[System.String],byref,byref)
          -6 (-0.32% of base) : System.Reflection.MetadataLoadContext.dasm - System.Reflection.TypeLoading.Ecma.EcmaCustomAttributeHelpers:TypeMatchesNameAndNamespace(System.Reflection.Metadata.EntityHandle,System.ReadOnlySpan`1[ubyte],System.ReadOnlySpan`1[ubyte],System.Reflection.Metadata.MetadataReader):bool
          -6 (-4.51% of base) : System.Security.Cryptography.dasm - System.Security.Cryptography.CngProperty:Equals(System.Security.Cryptography.CngProperty):bool:this
          -4 (-0.38% of base) : System.Private.CoreLib.dasm - System.Enum:TryParseByName[double](System.RuntimeType,System.ReadOnlySpan`1[ushort],bool,bool,byref):bool
          -4 (-0.38% of base) : System.Private.CoreLib.dasm - System.Enum:TryParseByName[int](System.RuntimeType,System.ReadOnlySpan`1[ushort],bool,bool,byref):bool
          -4 (-0.38% of base) : System.Private.CoreLib.dasm - System.Enum:TryParseByName[long](System.RuntimeType,System.ReadOnlySpan`1[ushort],bool,bool,byref):bool
          -4 (-0.37% of base) : System.Private.CoreLib.dasm - System.Enum:TryParseByName[short](System.RuntimeType,System.ReadOnlySpan`1[ushort],bool,bool,byref):bool

Top method regressions (percentages):
           5 ( 7.81% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:EqualsOrdinal(System.ReadOnlySpan`1[ushort],System.ReadOnlySpan`1[ushort]):bool
           2 ( 5.13% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[double](System.ReadOnlySpan`1[double],System.ReadOnlySpan`1[double]):bool
           2 ( 5.13% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[double](System.Span`1[double],System.ReadOnlySpan`1[double]):bool
           2 ( 5.13% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[System.Numerics.Vector`1[float]](System.ReadOnlySpan`1[System.Numerics.Vector`1[float]],System.ReadOnlySpan`1[System.Numerics.Vector`1[float]]):bool
           2 ( 5.13% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[System.Numerics.Vector`1[float]](System.Span`1[System.Numerics.Vector`1[float]],System.ReadOnlySpan`1[System.Numerics.Vector`1[float]]):bool
           2 ( 4.76% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[ubyte](System.ReadOnlySpan`1[ubyte],System.ReadOnlySpan`1[ubyte]):bool
           2 ( 4.76% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[ubyte](System.Span`1[ubyte],System.ReadOnlySpan`1[ubyte]):bool
           7 ( 4.55% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:Equals(Microsoft.Extensions.Primitives.StringSegment):bool:this
           2 ( 4.44% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[short](System.ReadOnlySpan`1[short],System.ReadOnlySpan`1[short]):bool
           2 ( 4.44% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[short](System.Span`1[short],System.ReadOnlySpan`1[short]):bool
           2 ( 4.35% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[int](System.ReadOnlySpan`1[int],System.ReadOnlySpan`1[int]):bool
           2 ( 4.35% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[int](System.Span`1[int],System.ReadOnlySpan`1[int]):bool
           2 ( 4.35% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[long](System.ReadOnlySpan`1[long],System.ReadOnlySpan`1[long]):bool
           2 ( 4.35% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:SequenceEqual[long](System.Span`1[long],System.ReadOnlySpan`1[long]):bool
           3 ( 3.95% of base) : System.Security.AccessControl.dasm - System.Security.AccessControl.CommonAcl:AceOpaquesMatch(System.Security.AccessControl.QualifiedAce,System.Security.AccessControl.QualifiedAce):bool

Top method improvements (percentages):
        -103 (-100.00% of base) : Microsoft.CodeAnalysis.dasm - Microsoft.CodeAnalysis.SmallDictionary`2[System.__Canon,int]:RightComplex(Microsoft.CodeAnalysis.SmallDictionary`2+AvlNode[System.__Canon,int]):Microsoft.CodeAnalysis.SmallDictionary`2+AvlNode[System.__Canon,int] (1 base, 0 diff methods)
          -4 (-5.88% of base) : System.Formats.Asn1.dasm - System.Formats.Asn1.AsnWriter:EncodedValueEquals(System.ReadOnlySpan`1[ubyte]):bool:this
          -6 (-4.51% of base) : System.Security.Cryptography.dasm - System.Security.Cryptography.CngProperty:Equals(System.Security.Cryptography.CngProperty):bool:this
          -7 (-4.35% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:op_Equality(Microsoft.Extensions.Primitives.StringSegment,Microsoft.Extensions.Primitives.StringSegment):bool
          -7 (-4.05% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:op_Inequality(Microsoft.Extensions.Primitives.StringSegment,Microsoft.Extensions.Primitives.StringSegment):bool
          -7 (-3.95% of base) : Microsoft.Extensions.Primitives.dasm - Microsoft.Extensions.Primitives.StringSegment:Equals(System.String):bool:this
         -14 (-3.47% of base) : System.Text.Json.dasm - System.Text.Json.JsonReaderHelper:TryGetFloatingPointConstant(System.ReadOnlySpan`1[ubyte],byref):bool (2 methods)
         -40 (-2.95% of base) : System.Text.Json.dasm - System.Text.Json.JsonDocument:TryGetNamedPropertyValue(int,int,System.ReadOnlySpan`1[ubyte],byref):bool:this
          -7 (-2.11% of base) : System.Private.CoreLib.dasm - System.String:MakeSeparatorListAny(System.ReadOnlySpan`1[ushort],System.ReadOnlySpan`1[System.String],byref,byref)
         -22 (-0.72% of base) : System.Reflection.MetadataLoadContext.dasm - System.Reflection.TypeLoading.Ecma.EcmaModule:GetTypeCoreNoCache(System.ReadOnlySpan`1[ubyte],System.ReadOnlySpan`1[ubyte],byref):System.Reflection.TypeLoading.RoDefinitionType:this
          -3 (-0.69% of base) : System.Text.Json.dasm - System.Text.Json.JsonSerializer:GetMetadataPropertyName(System.ReadOnlySpan`1[ubyte],System.Text.Json.Serialization.Metadata.PolymorphicTypeResolver):ubyte
          -8 (-0.58% of base) : System.Private.CoreLib.dasm - System.IO.Path:GetFullPath(System.String,System.String):System.String
          -3 (-0.56% of base) : System.Net.Security.dasm - System.Net.Security.TlsFrameHelper:TryGetApplicationProtocolsFromExtension(System.ReadOnlySpan`1[ubyte],byref):bool
          -3 (-0.55% of base) : System.Private.CoreLib.dasm - System.Text.EncodingTable:InternalGetCodePageFromName(System.String):int
          -3 (-0.47% of base) : System.Text.Json.dasm - System.Text.Json.Utf8JsonReader:ValueTextEquals(System.ReadOnlySpan`1[ushort]):bool:this

82 total methods with Code Size differences (26 improved, 56 regressed), 374821 unchanged

This PR triggered 23 new unrollings.

Example: https://www.diffchecker.com/525Bokla/

[EgorBo]

@stephentoub any thoughts on this? it triggered 23 new unrollings but in theory jit should be able to handle both patterns, but that will need quite some extra efforts

[stephentoub]

I'm fine with it if it doesn't regress anything meaningfully.

[EgorBo]

I'm fine with it if it doesn't regress anything meaningfully.

@stephentoub It should not (on all runtimes) and number of new unrollings prove it's better to speculate that "other.Length" is likely to be constant. Can you apporve it? 🙂 I needed it for #84525