Regression in System.Memory.Constructors<String>.ReadOnlyMemoryFromArray for Windows x86

[DrewScoggins]

System.Memory.Constructors.ReadOnlyMemoryFromArray has regressed by 34% from 3.0->31.

[DrewScoggins]

This test has shown a regression from the first run of our tests on this branch on 9/20 two days after the baseline 3.0 was run.

The builds you can use for comparison are in core-sdk and:

baseline: 04339c3a262a2e313f9431edd3805ce71e08b92e
compare: abd1e70d5fb3f8ef82f41d308f089c68e072ff4d

[danmoseley]

This is hard to explain, as there were very few changes in coreclr between 3.0 and 3.1. Certainly no changes to ReadOnlyMemory, but no other changes in corelib or vm that seem relevant. Only one change in JIT, that is not obviously x86 only. The test is very simple.

[GrabYourPitchforks]

We should have a unit test that makes sure we don't regress codegen from release to release.

[adamsitnik]

I was not able to reproduce it as of today while using lates versions of 2.1, 3.1 and 5.0:

py .\scripts\benchmarks_ci.py -f netcoreapp2.1 netcoreapp3.1 netcoreapp5.0 --filter 'System.Memory.Constructors<String>.ReadOnlyMemoryFromArray' --architecture x86 --bdn-arguments "--disasm true"

BenchmarkDotNet=v0.12.1.1405-nightly, OS=Windows 10.0.18363.959 (1909/November2019Update/19H2)
Intel Xeon CPU E5-1650 v4 3.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=5.0.100-rc.1.20413.9
  [Host]     : .NET Core 2.1.11 (CoreCLR 4.6.27617.04, CoreFX 4.6.27617.02), X86 RyuJIT
  Job-WNUJRF : .NET Core 2.1.11 (CoreCLR 4.6.27617.04, CoreFX 4.6.27617.02), X86 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Runtime=.NET Core 2.1  Arguments=/p:DebugType=portable  
Toolchain=netcoreapp2.1  IterationTime=250.0000 ms  MaxIterationCount=20  
MinIterationCount=15  WarmupCount=1  

Method	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated	Code Size
ReadOnlyMemoryFromArray	1.893 ns	0.0101 ns	0.0095 ns	1.893 ns	1.880 ns	1.916 ns	-	-	-	-	46 B

.NET Core 2.1.11 (CoreCLR 4.6.27617.04, CoreFX 4.6.27617.02), X86 RyuJIT

; System.Memory.Constructors`1[[System.__Canon, System.Private.CoreLib]].ReadOnlyMemoryFromArray()
       push      ebp
       mov       ebp,esp
       push      edi
       push      esi
       mov       eax,edx
       mov       edx,[ecx+4]
       test      edx,edx
       jne       short M00_L00
       xor       ecx,ecx
       xor       esi,esi
       xor       edi,edi
       jmp       short M00_L01
M00_L00:
       mov       ecx,edx
       xor       esi,esi
       mov       edi,[ecx+4]
M00_L01:
       lea       edx,[eax]
       call      CORINFO_HELP_CHECKED_ASSIGN_REF_ECX
       mov       [eax+4],esi
       mov       [eax+8],edi
       pop       esi
       pop       edi
       pop       ebp
       ret
; Total bytes of code 46

BenchmarkDotNet=v0.12.1.1405-nightly, OS=Windows 10.0.18363.959 (1909/November2019Update/19H2)
Intel Xeon CPU E5-1650 v4 3.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=5.0.100-rc.1.20413.9
  [Host]     : .NET Core 3.1.6 (CoreCLR 4.700.20.26901, CoreFX 4.700.20.31603), X86 RyuJIT
  Job-XZZIMO : .NET Core 3.1.6 (CoreCLR 4.700.20.26901, CoreFX 4.700.20.31603), X86 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Runtime=.NET Core 3.1  Arguments=/p:DebugType=portable  
Toolchain=netcoreapp3.1  IterationTime=250.0000 ms  MaxIterationCount=20  
MinIterationCount=15  WarmupCount=1  

Method	Mean	Error	StdDev	Median	Min	Max	Code Size	Gen 0	Gen 1	Gen 2	Allocated
ReadOnlyMemoryFromArray	1.299 ns	0.0077 ns	0.0064 ns	1.297 ns	1.290 ns	1.309 ns	44 B	-	-	-	-

.NET Core 3.1.6 (CoreCLR 4.700.20.26901, CoreFX 4.700.20.31603), X86 RyuJIT

; System.Memory.Constructors`1[[System.__Canon, System.Private.CoreLib]].ReadOnlyMemoryFromArray()
       push      ebp
       mov       ebp,esp
       push      edi
       push      esi
       mov       eax,edx
       mov       ecx,[ecx+4]
       test      ecx,ecx
       jne       short M00_L00
       xor       esi,esi
       xor       edi,edi
       jmp       short M00_L01
M00_L00:
       mov       esi,ecx
       mov       edi,[esi+4]
M00_L01:
       mov       edx,eax
       call      CORINFO_HELP_CHECKED_ASSIGN_REF_ESI
       xor       edx,edx
       mov       [eax+4],edx
       mov       [eax+8],edi
       pop       esi
       pop       edi
       pop       ebp
       ret
; Total bytes of code 44

BenchmarkDotNet=v0.12.1.1405-nightly, OS=Windows 10.0.18363.959 (1909/November2019Update/19H2)
Intel Xeon CPU E5-1650 v4 3.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=5.0.100-rc.1.20413.9
  [Host]     : .NET Core 5.0.0 (CoreCLR 5.0.20.40416, CoreFX 5.0.20.40416), X86 RyuJIT
  Job-HPWFEK : .NET Core 5.0.0 (CoreCLR 5.0.20.40416, CoreFX 5.0.20.40416), X86 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Runtime=.NET Core 5.0  Arguments=/p:DebugType=portable  
Toolchain=netcoreapp5.0  IterationTime=250.0000 ms  MaxIterationCount=20  
MinIterationCount=15  WarmupCount=1  

Method	Mean	Error	StdDev	Median	Min	Max	Code Size	Gen 0	Gen 1	Gen 2	Allocated
ReadOnlyMemoryFromArray	1.358 ns	0.0082 ns	0.0077 ns	1.357 ns	1.345 ns	1.370 ns	46 B	-	-	-	-

.NET Core 5.0.0 (CoreCLR 5.0.20.40416, CoreFX 5.0.20.40416), X86 RyuJIT

; System.Memory.Constructors`1[[System.__Canon, System.Private.CoreLib]].ReadOnlyMemoryFromArray()
       push      ebp
       mov       ebp,esp
       push      edi
       push      esi
       push      ebx
       mov       eax,edx
       mov       esi,[ecx+4]
       test      esi,esi
       jne       short M00_L00
       xor       edi,edi
       xor       ebx,ebx
       jmp       short M00_L01
M00_L00:
       mov       edi,esi
       mov       ebx,[edi+4]
M00_L01:
       mov       edx,eax
       call      CORINFO_HELP_CHECKED_ASSIGN_REF_EDI
       xor       edx,edx
       mov       [eax+4],edx
       mov       [eax+8],ebx
       pop       ebx
       pop       esi
       pop       edi
       pop       ebp
       ret
; Total bytes of code 46