+ implemented the logic to handle when we are really running out of memory.
  We need to be resilient to it during a GC. We might need an empty region
  per heap so we try to get it up front and if we can't get it and find out
  that we do need it, we resort to a special sweep mode.
+ also take virtual memory load into consideration
+ fixed the logic to decide whether we should compact based on space.
+ fixed various places when we can't get a region, we need to make sure we
  don't thread 0 into the region list.
+ made allocated_since_last_gc per more_space_lock otherwise we are not doing
  the accounting correctly
+ moved the pinning for STRESS_REGIONS into a blocking GC otherwise we can have
  AV from BGC trying to mark the pinned object while it's being constructed
+ got rid of the places that use the hard coded REGION_SIZE
+ included one perf change in reset_memory

During resolution, an interval should be marked inactive once there is no register assignment to the corresponding refPosition.

Fixes following failures:

https://helixre8s23ayyeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-pull-47307-head-9a04ddee2ee04376ae/System.Linq.Parallel.Tests/console.0e35ac6f.log?sv=2019-07-07&se=2021-03-15T02%3A22%3A01Z&sr=c&sp=rl&sig=zdrZjpHUrBJpYgQAvQb%2B81EHbJ%2FAhhe7BloSTARNazg%3D

Most artifacts produced by the PGO builds should now have 'PGO' prefixes or suffixes to distinguish them.

* Add new MemoryExtensions.SequenceEqual overloads

* Use MemoryExtensions.SequenceEqual in Enumerable.SequenceEqual

* Use MemoryExtensions.SequenceEqual in a few more places

[master] Update dependencies from mono/linker


 - Update linker arguments

 - Remove non needed arguments

Co-authored-by: NStephen Toub <stoub@microsoft.com>
Co-authored-by: NJeremy Barton <jbarton@microsoft.com>

* Support single file in DependencyModel

When used in a single file application, Assembly.CodeBase will throw an exception. Check for this situation by checking if Assembly.Location is empty before trying to probe next to the assembly.

Fix #47527

Co-authored-by: NMitchell Hwang <mitchell.hwang@microsoft.com>

* Update dependencies from https://github.com/dotnet/xharness build 20210226.1

Microsoft.DotNet.XHarness.CLI , Microsoft.DotNet.XHarness.TestRunners.Xunit
 From Version 1.0.0-prerelease.21125.1 -> To Version 1.0.0-prerelease.21126.1

* Update dependencies from https://github.com/dotnet/xharness build 20210226.2

Microsoft.DotNet.XHarness.CLI , Microsoft.DotNet.XHarness.TestRunners.Xunit
 From Version 1.0.0-prerelease.21125.1 -> To Version 1.0.0-prerelease.21126.2

* Update dependencies from https://github.com/dotnet/arcade build 20210225.5

Microsoft.DotNet.XUnitExtensions , Microsoft.DotNet.VersionTools.Tasks , Microsoft.DotNet.Build.Tasks.TargetFramework.Sdk , Microsoft.DotNet.Build.Tasks.Packaging , Microsoft.DotNet.Build.Tasks.Installers , Microsoft.DotNet.Build.Tasks.Feed , Microsoft.DotNet.Build.Tasks.Archives , Microsoft.DotNet.Arcade.Sdk , Microsoft.DotNet.ApiCompat , Microsoft.DotNet.CodeAnalysis , Microsoft.DotNet.XUnitConsoleRunner , Microsoft.DotNet.GenFacades , Microsoft.DotNet.GenAPI , Microsoft.DotNet.RemoteExecutor , Microsoft.DotNet.Helix.Sdk , Microsoft.DotNet.SharedFramework.Sdk
 From Version 6.0.0-beta.21120.1 -> To Version 6.0.0-beta.21125.5
Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Older CMake < 3.11 doesn't include COMPILE_OPTIONS source file property.
This property is needed by clang or it will issue warning when building
files with .c extension under c++ compiler.

Fallback to add_compile_options if CMake is older than 3.11. Even if
that option has wider scope, this is only applied to files in eventpipe
directory or in debug-pal.

Keeping the more precise set_source_files_properties on newer CMake and
when we can upgrade CMake to 3.11 or newer we could get rid of this.

Microsoft.DotNet.XHarness.CLI , Microsoft.DotNet.XHarness.TestRunners.Xunit
 From Version 1.0.0-prerelease.21124.1 -> To Version 1.0.0-prerelease.21125.1
Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Refactor download into a function.

Add newline after download is done.

Allow baseline JIT download to show it is being downloaded
(it was suppressed before).

* Build Threading.Tasks.DataFlow and ComponentModel.Annotations for NetCoreAppCurrent

Fix #48662

* Fix the build to enable FEATURE_TRACING.

Add EXTERNAL_DOTNET_MODIFIABLE_ASSEMBLIES env var for hot reload support

* Disable failing DNS tests on Linux

As there's currently no infrastructure to disable just for SLES,
disabling for its parent, which is Linux.

* Disable failing dns tests for sles only

- Add a document describing the behavior and how it is expected to be used.
- Rework the existing command line handling to implement the proposed create-mibc command. (the merge command is still entirely TBD).

- Don't use gtCloneExpr on trees that have persistent side effects
- Don't call gtCloneTree or fgMorphTree when we have an addrSpill case

* fix assertion merge for degenerate flow

* fix the dupCount condition

* Add comment and jitdump

* Fix memory leak in setVars

Crossgen2 owns the memory passed to it by JIT.

* setBoundaries has the same problem

Fixes #47584

This is support for putting the stress log into a memory mapped file and piping the dprintf calls in the GC codebase to the stress log.

It's much faster than the dprintf implementation we used before and doesn't take a lock for each dprintf call - only when it needs to get a new buffer. It also works for clrgc.dll, which accounts for some complications, because now calls can come from either coreclr.dll or clrgc.dll.

There is logic inside src/coreclr/util/StressLog.cpp to switch to the memory mapped file when the new environment variable COMPLUS_StressLogFilename is set. Here's a set of environment variables I've used:

COMPLUS_StressLogFilename=GCPerfSimStresslog.log
COMPLUS_gcServer=1
COMPLUS_LogLevel=9
COMPlus_StressLog=1
COMPlus_StressLogSize=10000000
COMPlus_TotalStressLogSize=1000000000

So this creates a max of 64 GB of stress log.

There is an analyzer tool to go with this under src/coreclr/tools/StressLogAnalyzer that is also part of this checkin. The tool is expected to become more sophisticated over time. The tool is itself multithreaded and uses a plugin dll for the actual analysis which makes it possible to change the plugin, rebuild and re-run the analysis on the in-memory log datastructure without reloading the log file.

The stresslog mechanism had a limit of 7 arguments so far, which seemed too small, so I've increased that to 12 currently. It can easily be increased up to 63, which is the limit in the format. The higher number of arguments is only supported when putting the stress log into a file, it is not yet supported when building the stress log in memory the traditional way. 

Supporting it would call for changes in SOS that I haven't done yet. However, stress logs containing no calls of more than 7 arguments would be dumped correctly by the current SOS - SOS would crash though with stress logs containing calls with more arguments. To catch this early, the logic in StressLog.cpp does a debug break when a call with more than 7 arguments is attempted without the memory-mapped file.

Note that for the purposes of GC logging, the logging level specified in the dprintf call is also persisted in the stress log. This makes it possible to selectively dump messages from specific subsystems.

Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

* Remove duplicated ILLink PackageReference

The Arcade.SDK already package refrences the ILLink package. The
duplicate reference in illink.targets caused SDK errors as the Arcade
reference has IsImplicitlyDefined set which doesn't allow an additional
reference with the same identity.

Also, as the ILLink package already exposes the path to the assembly via
its props file, using that instead of manually constructing the path to
the assembly.

The SDK target version update is required as the sequencing of the
ILLink.props file was wrong and is required for this change. This isn't
considered a breaking change, as the SDK's minimum required version
isn't changed.

* Update arcade dependencies

* Remove NuGet pack tasks pkgref

* Add mega hack workaround

* Remove KnownFrameworkReference items

* Don't hardcode SDK value in helix submission...

* Update runtimeConfiguration.targets

* Fix double publishing error in mobile tests

* Set DotNetCliVersion to right version for aspnetcoreruntime

* Update sendtohelixhelp.proj

* Update sendtohelixhelp.proj
Co-authored-by: NSantiago Fernandez Madero <safern@microsoft.com>

[master] Update dependencies from dotnet/runtime-assets dotnet/icu