JIT: Fold null checks for const strings

[EgorBo]

Similar to #37245 but now at the VN level so we can fold more, example:

class Program { public string Name; public void Foo(string name) { Name = name ?? throw new ArgumentNullException(nameof(name)); } public void Test() => Foo("hello"); }

Current codegen for Test:

; Method Program:Test():this G_M36831_IG01:   56 push rsi  4883EC20 sub rsp, 32 G_M36831_IG02:   48BAA85D6DCD69020000 mov rdx, 0x269CD6D5DA8  488B12 mov rdx, gword ptr [rdx]  4885D2 test rdx, rdx  7410 je SHORT G_M36831_IG05 G_M36831_IG03:   488D4908 lea rcx, bword ptr [rcx+8]  E82075515F call CORINFO_HELP_ASSIGN_REF  90 nop  G_M36831_IG04:   4883C420 add rsp, 32  5E pop rsi  C3 ret  G_M36831_IG05:   48B9104AFBE7F97F0000 mov rcx, 0x7FF9E7FB4A10  E84A79515F call CORINFO_HELP_NEWSFAST  488BF0 mov rsi, rax  B901000000 mov ecx, 1  48BAE0E235E8F97F0000 mov rdx, 0x7FF9E835E2E0  E8A3D9225F call CORINFO_HELP_STRCNS  488BD0 mov rdx, rax  488BCE mov rcx, rsi  E85874ADFF call System.ArgumentNullException:.ctor(System.String):this  488BCE mov rcx, rsi  E8B04C235F call CORINFO_HELP_THROW  CC int3 

New codegen:

; Method Program:Test():this G_M36831_IG01:  G_M36831_IG02:   48BAA85D71DA51010000 mov rdx, 0x151DA715DA8  488B12 mov rdx, gword ptr [rdx]  488D4908 lea rcx, bword ptr [rcx+8]  E82A75525F call CORINFO_HELP_ASSIGN_REF  90 nop  G_M36831_IG03:   C3 ret  ; Total bytes of code: 24

jit-diff (--pmi -f):

Summary of Code Size diffs: (Lower is better) Total bytes of base: 53004925 Total bytes of diff: 52999397 Total bytes of delta: -5528 (-0.01% of base) diff is an improvement. Top file improvements (bytes): -2164 : System.Private.Xml.dasm (-0.06% of base) -576 : System.Data.Common.dasm (-0.04% of base) -502 : System.Private.DataContractSerialization.dasm (-0.07% of base) -385 : Microsoft.CodeAnalysis.VisualBasic.dasm (-0.01% of base) -345 : Newtonsoft.Json.dasm (-0.04% of base) -332 : System.Speech.dasm (-0.08% of base) -201 : Microsoft.Extensions.Logging.Console.dasm (-0.44% of base) -192 : System.DirectoryServices.AccountManagement.dasm (-0.05% of base) -178 : System.DirectoryServices.dasm (-0.04% of base) -142 : System.Composition.AttributedModel.dasm (-18.11% of base) -119 : Microsoft.Extensions.Configuration.Xml.dasm (-1.11% of base) -80 : Microsoft.CodeAnalysis.CSharp.dasm (-0.00% of base) -72 : System.Private.CoreLib.dasm (-0.00% of base) -62 : System.DirectoryServices.Protocols.dasm (-0.07% of base) -46 : System.Configuration.ConfigurationManager.dasm (-0.01% of base) -42 : System.Net.Primitives.dasm (-0.07% of base) -18 : System.Private.Uri.dasm (-0.02% of base) -18 : Microsoft.CSharp.dasm (-0.00% of base) -18 : xunit.runner.utility.netcoreapp10.dasm (-0.01% of base) -15 : CommandLine.dasm (-0.00% of base) 23 total files with Code Size differences (23 improved, 0 regressed), 248 unchanged. Top method improvements (bytes): -954 (-21.54% of base) : System.Private.Xml.dasm - TypeScope:AddSoapEncodedTypes(String) -230 (-3.54% of base) : Newtonsoft.Json.dasm - <ExecuteFilter>d__4:MoveNext():bool:this (8 methods) -216 (-10.15% of base) : System.Private.Xml.dasm - DatatypeImplementation:CreateBuiltinTypes() -216 (-11.99% of base) : System.Private.Xml.dasm - Preprocessor:GetBuildInSchema():XmlSchema -144 (-13.30% of base) : System.Private.Xml.dasm - XmlSchemaValidator:BuildXsiAttributes() -144 (-16.29% of base) : System.Speech.dasm - SAPICategories:CompareTokenVersions(ObjectToken,ObjectToken,byref):int -119 (-4.45% of base) : Microsoft.Extensions.Configuration.Xml.dasm - XmlStreamConfigurationProvider:Read(Stream,XmlDocumentDecryptor):IDictionary`2 -115 (-5.94% of base) : Newtonsoft.Json.dasm - <ExecuteFilter>d__12:MoveNext():bool:this -94 (-6.62% of base) : System.Private.Xml.dasm - XmlSchemaObjectComparer:NameOf(XmlSchemaObject):XmlQualifiedName -72 (-7.28% of base) : System.Speech.dasm - VoiceInfo:.ctor(ObjectToken):this -71 (-67.62% of base) : System.Composition.AttributedModel.dasm - SharedAttribute:.ctor():this -71 (-60.68% of base) : System.Composition.AttributedModel.dasm - SharedAttribute:.ctor(String):this -67 (-30.59% of base) : Microsoft.Extensions.Logging.Console.dasm - JsonConsoleFormatter:.ctor(IOptionsMonitor`1):this -67 (-30.59% of base) : Microsoft.Extensions.Logging.Console.dasm - SimpleConsoleFormatter:.ctor(IOptionsMonitor`1):this -67 (-30.59% of base) : Microsoft.Extensions.Logging.Console.dasm - SystemdConsoleFormatter:.ctor(IOptionsMonitor`1):this -62 (-12.53% of base) : System.DirectoryServices.Protocols.dasm - AddRequest:.ctor(String,String):this -60 (-8.16% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Scanner:ScanInterpolatedStringPunctuation():SyntaxToken:this -50 (-1.44% of base) : System.DirectoryServices.AccountManagement.dasm - ADStoreCtx:GetGroupsMemberOf(Principal,StoreCtx):ResultSet:this -46 (-2.54% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Scanner:ScanXmlElementInXmlDoc(int):SyntaxToken:this -44 (-1.07% of base) : System.Private.Xml.dasm - ReflectionXmlSerializationReader:WriteLiteralStructMethod(StructMapping,bool,bool,String):Object:this Top method improvements (percentages): -71 (-67.62% of base) : System.Composition.AttributedModel.dasm - SharedAttribute:.ctor():this -71 (-60.68% of base) : System.Composition.AttributedModel.dasm - SharedAttribute:.ctor(String):this -28 (-50.00% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Scanner:MakeEndOfInterpolatedStringToken():SyntaxToken:this -36 (-32.14% of base) : System.Data.Common.dasm - SqlChars:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlDateTime:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlDecimal:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlDouble:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlGuid:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlInt16:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlInt32:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlInt64:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlMoney:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlSingle:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlString:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlXml:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlBinary:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlBoolean:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlByte:GetXsdType(XmlSchemaSet):XmlQualifiedName -36 (-32.14% of base) : System.Data.Common.dasm - SqlBytes:GetXsdType(XmlSchemaSet):XmlQualifiedName -67 (-30.59% of base) : Microsoft.Extensions.Logging.Console.dasm - JsonConsoleFormatter:.ctor(IOptionsMonitor`1):this 142 total methods with Code Size differences (142 improved, 0 regressed), 268410 unchanged. 

[davidfowl]

Wow this looks great

[ShreyasJejurkar]

Hi @EgorBo, this looks amazing! I always like folding code as much as possible, for faster results!
Some days ago, I pinged you with one of my finding, I tried to implement that but I failed because am quite to JIT stuff! 😅
Hope you will have some thoughts on it like it's better or bad to have this much of folding.
Link to that tweet => https://twitter.com/MCCshreyas/status/1350021589987778566

[EgorBo]

@MCCshreyas feel free to file an issue 🙂

[sandreenko]

LGTM

[benaadams]

🥳