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Cache SubstitutedNamedTypeSymbol.GetMembers to avoid unnecessary allocations #69164

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merged 3 commits into from
Aug 14, 2023

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Fixes #69163

@Youssef1313 Youssef1313 requested a review from a team as a code owner July 22, 2023 08:15
@dotnet-issue-labeler dotnet-issue-labeler bot added Area-Compilers untriaged Issues and PRs which have not yet been triaged by a lead labels Jul 22, 2023
@ghost ghost added the Community The pull request was submitted by a contributor who is not a Microsoft employee. label Jul 22, 2023
@Youssef1313 Youssef1313 marked this pull request as draft July 22, 2023 09:04
@Youssef1313 Youssef1313 marked this pull request as ready for review July 22, 2023 14:27
if (!_lazyMembers.IsDefault)
{
// If we already calculated the ordered members, return it directly.
return _lazyMembers;
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@AlekseyTs AlekseyTs Jul 24, 2023

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_lazyMembers

I think we should do ConditionallyDeOrder in this case. #Closed

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Yup makes sense. Thanks!

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Done with review pass (commit 1)

if (!_lazyMembers.IsDefault)
{
// If we already calculated the ordered members, return it directly.
return _lazyMembers.ConditionallyDeOrder();
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I realize the comment for GetMembersUnordered() states the order may change from call to call, but this may be the first implementation where that is the case (the order will be different before and after _lazyMembers is populated). Is that a concern?

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Is that a concern?

We do not expose GetMembersUnordered to external consumers. However, there is still a chance that an internal implementation somewhere took a dependency on getting items in the same order each time. Reviewing existing call sites might help. What do you think?

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Reviewing existing call sites might help.

There are 50 callsites for NamespaceOrTypeSymbol.GetMembersUnordered(), and a few of those are methods that return that value so the number of use-sites may be too many to review easily. That said, I skimmed through the direct callers of GetMembersUnordered() and didn’t see any obvious issues.

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@cston cston Jul 26, 2023

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@Youssef1313, it looks like the perf issue is allocations from GetMembers() and not GetMembersUnordered(). Given that, to avoid the risk of breaking callers of GetMembersUnordered(), let's revert the change to GetMembersUnordered(), and always recalculate that array rather than using _lazyMembers if available. Thanks.

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Done with review pass (commit 2)

@jcouv jcouv added this to the 17.8 milestone Jul 26, 2023
@jcouv jcouv removed the untriaged Issues and PRs which have not yet been triaged by a lead label Jul 26, 2023
cston
cston previously approved these changes Jul 26, 2023
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LGTM (commit 2)

@cston cston self-requested a review July 26, 2023 17:56
@cston cston dismissed their stale review July 26, 2023 17:57

Adding comment.

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@cston Sorry for leaving this one for long. I addressed your comment.

Is this ready to merge now?

@cston cston merged commit b91897c into dotnet:main Aug 14, 2023
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@ghost ghost modified the milestones: 17.8, Next Aug 14, 2023
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cston commented Aug 14, 2023

Thanks @Youssef1313.

@Youssef1313 Youssef1313 deleted the perf-getmembers branch August 15, 2023 02:05
@dibarbet dibarbet removed this from the Next milestone Aug 28, 2023
@dibarbet dibarbet added this to the 17.8 P2 milestone Aug 28, 2023
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SubstitutedNamedTypeSymbol.GetMembers isn't cached causing 4% allocations of SubstitutedMethodSymbol
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