Scalar replacement of aggregates

[DemiMarie]

This is a feature request for scalar replacement of aggregates in RyuJIT. RyuJIT currently does not optimize value types very well, and this will hopefully fix this.

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[pgavlin]

cc @CarolEidt @dotnet/jit-contrib

RyuJIT does perform some limited SROA, but the terminology is different: RyuJIT refers to this optimization as "struct promotion".

[DemiMarie]

I was thinking of full SROA, at least where that would be beneficial.

On Aug 15, 2016 3:16 PM, "Pat Gavlin" notifications@github.com wrote:

cc @CarolEidt https://github.com/CarolEidt @dotnet/jit-contrib
https://github.com/orgs/dotnet/teams/jit-contrib

RyuJIT does perform some limited SROA, but the terminology is different:
RyuJIT refers to this optimization as "struct promotion".

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[CarolEidt]

@DemiMarie - as @pgavlin mentions, this is called "struct promotion" in RyuJIT, and it is limited in what it will do. Some of the fundamental constraints are:

• The struct must not be address-taken (and it is currently somewhat conservative about what it considers to be address-taking, which could be improved).
• It must have no overlapping fields.

Some of the heuristic or implementation-limited constraints are:

• It must have only primitive fields.
• It must not be an argument or a return value that is passed in registers.
• It can't be larger than 32 bytes.
• It can't have more than 4 fields.

We expect to make improvements in this area relatively soon, but if there are specific scenarios you're interested (especially if you have some code, ideally in the form of a benchmark, that demonstrates it) we'd love to hear about it.

If you're interested in the work that I'm currently doing to improve code generation for structs (aka value types), see https://github.com/dotnet/coreclr/blob/master/Documentation/design-docs/first-class-structs.md

[BruceForstall]

Given that we already have struct promotion, and various documents and issues discussing improvements, I'm going to close this.