What's new in .NET 6 Preview 6 [WIP]

[leecow]

What's new in .NET 6 Preview 6

This issue is for teams to highlight work for the community that will release .NET 6 Preview 6.

To add content, use a new conversation entry. The entry should include the team name and feature title as the first line as shown in the template below.

## Team Name: Feature title

[link to the tracking issue or epic item for the work]

Tell the story of the feature and anything the community should pay particular attention 
to be successful using the feature.

Preview 1: #5853
Preview 2: #5889
Preview 3: #5890
Preview 4: #6098
Preview 5: #6099
Preview 7: #6444

[joperezr]

Added TLS support for System.DirectoryServices.Protocols in Unix, which was one of the biggest gaps between the Windows and new Unix implementation. PR: dotnet/runtime#52904

Provided by community member @iinuwa

[mangod9]

crossgen2 is the only option for PublishReadyToRun starting preview6

As we continue the journey of enabling crossgen2, we have now removed crossgen from the Microsoft.NETCore.App package. As part of this change the SDK doesnt support using crossgen for PublishReadyToRun. You still have the ability to choose composite or non-composite.

      <PublishReadyToRun>true</PublishReadyToRun> 
      <PublishReadyToRunComposite>false</PublishReadyToRunComposite> <!-- swtich to true to generate a composite R2R image -->
      <PublishReadyToRunUseCrossgen2>true</PublishReadyToRunUseCrossgen2> <!-- This is a NOP -->

[JulieLeeMSFT]

CodeGen

Dynamic PGO dotnet/runtime#43618

• Add option to choose guarded devirt class randomly JIT: add option to choose guarded devirt class randomly runtime#53399
• pgo/devirt diagnostic improvements JIT: pgo/devirt diagnostic improvements runtime#53247

(Modified LSRA content in #6325 (comment))
### LSRA dotnet/runtime#43318
- Refactor LSRA's heuristics selection dotnet/runtime#52832
-- Now, DEBUG mode includes a COMPlus variable that LsraOrdering will let the user set the heuristics ordering.

W^X

• Generate JITted code into a scratch buffer in preparation of the W^X work. JIT into scratch buffer runtime#53173

[kouvel]

Threading

Improved the rate of thread injection for blocking due to sync-over-async (dotnet/runtime#53471)

• Sync-over-async is a common type of blocking work. When it happens on thread pool worker threads it can lead to starvation, and the slow thread injection may delay other queued work from running, also delaying the starvation from being resolved.
• This change improved the rate of thread injection by default when sync-over-async is the only type of blocking work happening on thread pool worker threads. There are some new AppContext config values that can be used to configure the rate of thread injection in response to sync-over-async.

[JulieLeeMSFT]

CodeGen

LSRA

• Refactor LSRA's heuristics selection Refactor LSRA's heuristics selection runtime#52832
  • Now, DEBUG mode includes a COMPlus variable that LsraOrdering will let the user set the heuristics ordering.
• Tune the heuristics for register to select optimal register candidate to spill. Consider reloadWeight while evaluating spill cost runtime#53853

More details: windows x86 improvements, windows x64 improvements and here.

Code quality

• Eliminate redundant “test” instruction if previous instruction updates the zero-flag “ZF”. Eliminate redundant test instruction runtime#53214

[marcpopMSFT]

.NET SDK Optional Workload improvements

Building on the work that released in preview 4 for optional workloads and the new features of list and update that we added for preview 5, we have added three new commands for preview 6
dotnet workload search will show the list of workloads available to install
dotnet workload repair will re-install all workloads you've previously installed. This is useful if your install fails in the middle because of a dropped internet connection. Optional workloads are made up of multiple workload packs and you may have gotten into a state where some installed successfully but others didn't.
dotnet workload uninstall will remove the specified workload from your system to free up space if you no longer require a workload.