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Avoid creating a result temp for is-expressions #68694

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merged 26 commits into from
Aug 11, 2023
Merged

Avoid creating a result temp for is-expressions #68694

merged 26 commits into from
Aug 11, 2023

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alrz
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@alrz alrz commented Jun 20, 2023 •
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Closes #59615
Closes #55334

The idea is that while the expression is still spilled, the expression is no longer spilled by default and the boolean result will be pushed to the stack. The input expression will be evaluated as sequence side effects which will in turn spill if necessary. As a result, codegen is now closer to binary expressions' (but not quite).

The same optimization could be applied to switch expression - looking at conditionals, we will have to merge stack type for that to work. I'll leave it out of this PR for now, I'm new to this so there may be a better way to accomplish the same.

Thanks.

@alrz alrz requested a review from a team as a code owner June 20, 2023 11:37
@dotnet-issue-labeler dotnet-issue-labeler bot added Area-Compilers untriaged Issues and PRs which have not yet been triaged by a lead labels Jun 20, 2023
@ghost ghost added the Community The pull request was submitted by a contributor who is not a Microsoft employee. label Jun 20, 2023
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@alrz It looks like there are legitimate test failures and Correctness leg errors.

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Done with review pass (commit 2), tests are not looked at.

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AlekseyTs commented Jun 21, 2023 •
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I am not feeling comfortable with the taken approach. I suggest to look for an alternatives.

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How could I reproduce the bootstrap build locally?

The build script has a-bootstrap switch. Debugging the failure could be tricky though. If I remember correctly I did something like:

  1. Figure out what project cannot be built
  2. Build it under debugger with the new compiler

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alrz commented Jun 22, 2023 •
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I am not felling comfortable with the taken approach. I suggest to look for an alternatives.

Short-circuiting is probably best to be done as a rewrite to expression (which doesn't always work because we may have a SwitchDispatch that could turn to an expression in emitter for range checks, which makes me wonder if this optimization should be done in a later pass), for any other case I think Optimizer should be taught to inline the temp when possible. Would that need a new node?

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Would that need a new node?

If we are talking about an optimization as a special pass post regular rewrite (BTW, we already have a pass like that), I hope the optimization could be implemented as looking for a pattern in the bound tree and rewriting portion of the tree. That, generally, shouldn't need a new node. But, who knows, complexity could be so high that having a some sort of hint might help.
In general, introducing new nodes that survive regular rewrite has extra cost and risk, the optimizer might start "failing" on them.

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@alrz alrz marked this pull request as draft June 23, 2023 11:00
@alrz alrz force-pushed the dag-lowering branch 2 times, most recently from 5735b22 to 5f13ffe Compare June 26, 2023 16:09
@alrz alrz marked this pull request as ready for review June 28, 2023 22:14
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alrz commented Jun 28, 2023 •
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@AlekseyTs Took a different approach to address avoiding spilling temps and including destinations in the same node.
Please take a look when you had a chance. Thanks.

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Done with review pass (commit 24)

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alrz commented Jul 18, 2023

@AlekseyTs @dotnet/roslyn-compiler for review, thanks.

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LGTM (commit 26)

@jcouv jcouv self-assigned this Jul 18, 2023
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@dotnet/roslyn-compiler For the second review

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alrz commented Jul 24, 2023

Opened follow-up for switch-expressions: #69194

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alrz commented Jul 25, 2023 •
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In #69194, bootstrap build fails where iterator/using are mixed (at least the one cause that I'm aware of). Is there anything special to do to cover this in either PRs?

(Added the details in #69194, but I think it could help to validate this PR as well)

@alrz alrz mentioned this pull request Jul 25, 2023
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@jaredpar jaredpar modified the milestones: 17.8, 17.9 Aug 9, 2023
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LGTM Thanks (iteration 26)

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jcouv commented Aug 11, 2023

/azp run

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@jcouv jcouv enabled auto-merge (squash) August 11, 2023 17:49
@jcouv jcouv merged commit e1031a7 into dotnet:main Aug 11, 2023
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@ghost ghost modified the milestones: 17.9, Next Aug 11, 2023
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Revert "Avoid creating a result temp for is-expressions (#68694)"
794d6be 
This reverts commit e1031a7.
@RikkiGibson RikkiGibson mentioned this pull request Aug 17, 2023
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Revert "Avoid creating a result temp for is-expressions (dotnet#68694)"
4e45384 
This reverts commit e1031a7.
RikkiGibson added a commit that referenced this pull request Aug 18, 2023
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Revert "Avoid creating a result temp for is-expressions (#68694)" (#6…
b4a9c62 
…9582)

This reverts commit e1031a7.
@dibarbet dibarbet modified the milestones: Next, 17.8 P2 Aug 28, 2023
@alrz alrz mentioned this pull request Feb 26, 2024
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Reapply "Avoid creating a result temp for is-expressions (dotnet#68694)…
bb65732 
…" (dotnet#69582)

This reverts commit b4a9c62.
AlekseyTs added a commit that referenced this pull request Mar 7, 2024
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Revert "Revert "Avoid creating a result temp for is-expressions (#68694…
debc738 
…)" (#6…"

This reverts commit b4a9c62.
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