Improve JIT loop optimizations (.NET 8)

[BruceForstall]

As we did for .NET 6 and .NET 7, we plan to continue improving JIT optimization capabilities for loop code. An overview of many JIT optimization possibilities is here; this issue will focus on issues we choose to address in .NET 8.

Planned for .NET 8

Multi-dimensional array improvements

• Remove old multi-dimensional array code #71678

Loop recognition and canonicalization

• Loop canonicalization should always create loop pre-headers #77033 Always create pre-headers
• Change loop cloning to work with pre-header blocks #62665 Change loop cloning to work with pre-header blocks

Cut for .NET 8

Loop cloning

• Loops aren't cloned for Spans #82946 Support loop cloning for Span

Multi-dimensional array improvements

• RyuJIT: support cloning loop nests with multi-dimensional array accesses #71674
• Improve hoisting, CSE, LSRA for MD array accesses #71676

Loop recognition and canonicalization

• Certain loops do not get recorded in optLoopTable #43713 Describes two cases where loops are missed due to various issues.
  • [JIT] Asm difference for F# and C# methods #58941 F# loops not recognized

Loop cloning

• Support loop cloning of class member arrays #77071 Clone arrays with class member arrays.
• Consider rebuilding loop table after loop cloning #62615

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Issue Details

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As we did for .NET 6 and .NET 7, we plan to continue improving JIT optimization capabilities for loop code. An overview of many JIT optimization possibilities is here; this issue will focus on issues we choose to address in .NET 8.

Planned for .NET 8

• RyuJIT: support cloning loop nests with multi-dimensional array accesses #71674
• Certain loops do not get recorded in optLoopTable #43713 Describes two cases where loops are missed due to various issues.
  • [JIT] Asm difference for F# and C# methods #58941 F# loops not recognized

Author:	BruceForstall
Assignees:	-
Labels:	area-CodeGen-coreclr, User Story
Milestone:	8.0.0

[jakobbotsch]

@BruceForstall #9977 is a benchmark for the span loop cloning, so it might be appropriate to put it in .NET 8 milestone too as part of #82946.

[BruceForstall]

No more work is planned here for .NET 8. A new issue will be created for .NET 9 as appropriate.