JIT: simple redundant compare optimization

[AndyAyersMS]

For a relop, walk up the dominator tree to see if any dominating
block has a similar compare. If so, and there's just one path from
that block to the relop, the relop's value is known.

Closes #11909.

[AndyAyersMS]

@briansull PTAL.
cc @dotnet/jit-contrib

This will eventually feed into optimizing redundant class checks we'll see in dynamic PGO.

PMI CodeSize Diffs for System.Private.CoreLib.dll, framework assemblies for x64 default jit Summary of Code Size diffs: (Lower is better) Total bytes of base: 50312241 Total bytes of diff: 50302279 Total bytes of delta: -9962 (-0.02% of base) diff is an improvement. Top file improvements (bytes): -4129 : System.Data.Common.dasm (-0.28% of base) -3542 : FSharp.Core.dasm (-0.11% of base) -637 : System.Private.CoreLib.dasm (-0.01% of base) -274 : Microsoft.CodeAnalysis.CSharp.dasm (-0.01% of base) -258 : Microsoft.CodeAnalysis.VisualBasic.dasm (-0.00% of base) -154 : System.Text.Json.dasm (-0.03% of base) -104 : System.Security.Cryptography.Pkcs.dasm (-0.03% of base) -89 : Microsoft.Extensions.DependencyModel.dasm (-0.19% of base) -75 : System.Formats.Asn1.dasm (-0.08% of base) -63 : System.Net.Http.dasm (-0.01% of base) -61 : System.DirectoryServices.AccountManagement.dasm (-0.02% of base) -59 : System.Linq.Expressions.dasm (-0.01% of base) -38 : Microsoft.Extensions.Logging.Console.dasm (-0.09% of base) -36 : System.Diagnostics.Process.dasm (-0.04% of base) -35 : Microsoft.Diagnostics.Tracing.TraceEvent.dasm (-0.00% of base) -33 : System.Private.Xml.dasm (-0.00% of base) -30 : System.Memory.dasm (-0.01% of base) -28 : System.Text.Encodings.Web.dasm (-0.09% of base) -27 : System.Security.Cryptography.Algorithms.dasm (-0.01% of base) -27 : System.Security.Cryptography.Cng.dasm (-0.02% of base) 42 total files with Code Size differences (42 improved, 0 regressed), 226 unchanged. Top method improvements (bytes): -529 (-14.86% of base) : System.Data.Common.dasm - SqlDoubleStorage:Aggregate(ref,int):Object:this -449 (-12.49% of base) : System.Data.Common.dasm - SqlSingleStorage:Aggregate(ref,int):Object:this -446 (-13.78% of base) : System.Data.Common.dasm - SqlInt16Storage:Aggregate(ref,int):Object:this -446 (-13.79% of base) : System.Data.Common.dasm - SqlInt32Storage:Aggregate(ref,int):Object:this -446 (-12.31% of base) : System.Data.Common.dasm - SqlInt64Storage:Aggregate(ref,int):Object:this -446 (-11.65% of base) : System.Data.Common.dasm - SqlMoneyStorage:Aggregate(ref,int):Object:this -446 (-13.72% of base) : System.Data.Common.dasm - SqlByteStorage:Aggregate(ref,int):Object:this -440 (-11.14% of base) : System.Data.Common.dasm - SqlDecimalStorage:Aggregate(ref,int):Object:this -203 (-5.40% of base) : System.Private.CoreLib.dasm - TextInfo:ChangeCaseCommon(String):String:this (7 methods) -151 (-44.41% of base) : System.Data.Common.dasm - DataTable:FindByIndex(Index,ref):DataRow:this -139 (-20.20% of base) : System.Data.Common.dasm - DataView:System.ComponentModel.IBindingList.Find(PropertyDescriptor,Object):int:this -134 (-9.48% of base) : System.Data.Common.dasm - DataTable:LoadRow(ref,int,Index):DataRow:this -130 (-20.57% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkEqualsQmark(Nullable`1,Nullable`1):bool (6 methods) -127 (-12.99% of base) : System.Private.CoreLib.dasm - Vector128`1:<Equals>g__SoftwareFallback|12_0(byref,Vector128`1):bool (6 methods) -95 (-21.16% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreaterEqualsQmark(Nullable`1,Nullable`1):bool (6 methods) -95 (-21.16% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreaterQmark(Nullable`1,Nullable`1):bool (6 methods) -95 (-21.16% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLessEqualsQmark(Nullable`1,Nullable`1):bool (6 methods) -95 (-21.16% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLessQmark(Nullable`1,Nullable`1):bool (6 methods) -87 (-10.48% of base) : System.Private.CoreLib.dasm - Vector256`1:<Equals>g__SoftwareFallback|14_0(byref,Vector256`1):bool (6 methods) -82 (-3.63% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - CodeGenerator:EmitTryCastExpression(BoundTryCast,bool):this Top method improvements (percentages): -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreaterEquals(Nullable`1,long):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreater(Nullable`1,long):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLessEquals(Nullable`1,long):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLess(Nullable`1,long):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkEquals(Nullable`1,long):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_GreaterEqualsQmark(long,Nullable`1):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_GreaterQmark(long,Nullable`1):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_LessEqualsQmark(long,Nullable`1):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_LessQmark(long,Nullable`1):bool -22 (-50.00% of base) : FSharp.Core.dasm - NullableOperators:op_EqualsQmark(long,Nullable`1):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreaterEquals(Nullable`1,double):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkGreater(Nullable`1,double):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLessEquals(Nullable`1,double):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkLess(Nullable`1,double):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkEquals(Nullable`1,int):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_QmarkEquals(Nullable`1,double):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_GreaterEqualsQmark(double,Nullable`1):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_GreaterQmark(double,Nullable`1):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_LessEqualsQmark(double,Nullable`1):bool -22 (-45.83% of base) : FSharp.Core.dasm - NullableOperators:op_LessQmark(double,Nullable`1):bool 257 total methods with Code Size differences (257 improved, 0 regressed), 258511 unchanged. 

Diff from #11909

; Assembly listing for method String:EndsWith(String,int):bool:this ;; BEFORE G_M26632_IG11:  mov ebx, dword ptr [rdi+8]  mov r8d, ebx  sub r8d, r9d  cmp ebx, r8d  jb SHORT G_M26632_IG16  cmp ebx, r8d  jb G_M26632_IG22 G_M26632_IG12:  add rdi, 12 ;; AFTER G_M26632_IG11:  mov ebx, dword ptr [rdi+8]  mov r8d, ebx  sub r8d, r9d  cmp ebx, r8d  jb SHORT G_M26632_IG15  add rdi, 12

[AndyAyersMS]

Note it feels a bit odd to be doing this opt here, as it's not strictly related to assertion prop, but it doesn't seem to warrant its own phase. Feel free to suggest a better home.

[AndyAyersMS]

@dotnet/jit-contrib anyone able to take a look?

[briansull]

Approved with doc suggestion

[briansull]

You should update the method header to the standard header and under Note: add comment saying that we also do this special case optimization.

[AndyAyersMS]

One test failure on x64 osx: profiler/elt/slowpatheltleave/slowpatheltleave.sh

This test seems to fail sporadically once a day or so. It looks like the test "passes" but then perhaps the runtime crashes on exit?

@davmason is this on your radar?

[davmason]

@davmason is this on your radar?

No, I haven't seen that before. I'll take a look

[AndyAyersMS]

I'm going to merge as the one failure above does not seem related.

[benaadams]

@AndyAyersMS should have also fixed #35348