string.EndsWith use SequenceEqual not SequenceCompareTo

[benaadams]

for Ordinal.

CompareOrdinalHelper goes via SequenceCompareTo and is then tested if zero

Is more efficient to just find if they are the same; as CompareTo needs to find where they differ and then if >/==/< at that character.

/cc @jkotas @stephentoub

[benaadams]

It now generates these checks

; Assembly listing for method String:EndsWith(ref,int):bool:this
...
G_M23680_IG10:
       mov      ecx, dword ptr [rsi+8]
       sub      ecx, r8d
       cmp      dword ptr [rsi+8], ecx   ; should eliminate one below?
       jb       SHORT G_M23680_IG15
       cmp      dword ptr [rsi+8], ecx   ; should be eliminated?
       jb       G_M23680_IG22
G_M23680_IG11:

I assume the first should eliminate the second? /cc @AndyAyersMS @mikedn

[benaadams]

Otherwise it calls into SequenceEquals happily

G_M23680_IG10:
       mov      ecx, dword ptr [rsi+8]
       sub      ecx, r8d
       cmp      dword ptr [rsi+8], ecx
       jb       SHORT G_M23680_IG15
       cmp      dword ptr [rsi+8], ecx
       jb       G_M23680_IG22
G_M23680_IG11:
       lea      rdx, bword ptr [rsi+12]
       mov      eax, dword ptr [rsi+8]
       sub      eax, ecx
       movsxd   rcx, ecx
       lea      rcx, bword ptr [rdx+2*rcx]
       lea      rdx, bword ptr [rdi+12]
       cmp      eax, r8d
       jne      SHORT G_M23680_IG12
       movsxd   r8, eax
       shl      r8, 1
       call     [SpanHelpers:SequenceEqual(byref,byref,long):bool]
       movzx    rdx, al
       jmp      SHORT G_M23680_IG13
G_M23680_IG12:
       xor      edx, edx
G_M23680_IG13:
       mov      ebp, edx
       jmp      SHORT G_M23680_IG17

[benaadams]

Two infra? issues on coreclr-ci

Test pri0 Linux arm64 checked Job
Agent: Hosted Ubuntu 1604 6

Send tests to Helix - 1 error

/home/vsts_azpcontainer/.nuget/packages/microsoft.dotnet.helix.sdk/2.0.0-beta.19067.6/tools/Microsoft.DotNet.Helix.Sdk.MultiQueue.targets(87,5): 
 error : RestApiException: An Unexpected error occured when processing the request. [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.WorkItem.ListInternalAsync(String job, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/WorkItem.cs:line 89 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.WorkItem.ListAsync(String job, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/WorkItem.cs:line 47 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.HelixApi.RetryAsync[T](Func`1 function, Action`1 logRetry, Func`2 isRetryable) [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixWait.WaitForHelixJobAsync(String jobName) in /_/src/Microsoft.DotNet.Helix/Sdk/HelixWait.cs:line 70 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixWait.ExecuteCore() in /_/src/Microsoft.DotNet.Helix/Sdk/HelixWait.cs:line 60 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixTask.Execute() in /_/src/Microsoft.DotNet.Helix/Sdk/HelixTask.cs:line 43 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :  [/__w/1/s/tests/helixpublishwitharcade.proj]
  Job be118ae5-6965-407c-8b1d-e2ff6eec0922 is completed with 57 finished work items.

Build FAILED.

Test Pri0 Linux x64 checked Job
Agent: Hosted Ubuntu 1604 2

Send tests to Helix - 1 error

...
  Job 0c0c5f5e-9943-4492-bb31-58f4a8c0ccab is completed with 57 finished work items.
/home/vsts_azpcontainer/.nuget/packages/microsoft.dotnet.helix.sdk/2.0.0-beta.19067.6/tools/Microsoft.DotNet.Helix.Sdk.MultiQueue.targets(87,5):
 error : RestApiException: An Unexpected error occured when processing the request. [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.WorkItem.ListInternalAsync(String job, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/WorkItem.cs:line 89 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.WorkItem.ListAsync(String job, CancellationToken cancellationToken) in /_/src/Microsoft.DotNet.Helix/Client/CSharp/generated-code/WorkItem.cs:line 47 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Client.HelixApi.RetryAsync[T](Func`1 function, Action`1 logRetry, Func`2 isRetryable) [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixWait.WaitForHelixJobAsync(String jobName) in /_/src/Microsoft.DotNet.Helix/Sdk/HelixWait.cs:line 70 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixWait.ExecuteCore() in /_/src/Microsoft.DotNet.Helix/Sdk/HelixWait.cs:line 60 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :    at Microsoft.DotNet.Helix.Sdk.HelixTask.Execute() in /_/src/Microsoft.DotNet.Helix/Sdk/HelixTask.cs:line 43 [/__w/1/s/tests/helixpublishwitharcade.proj]
 error :  [/__w/1/s/tests/helixpublishwitharcade.proj]
  Job 3f5e37d4-3cdd-4fa4-b837-d04fad1dbb04 is completed with 57 finished work items.

Build FAILED.

[benaadams]

Raised issue for the double check https://github.com/dotnet/coreclr/issues/22246

[jkotas]

Thanks @benaadams !