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cmd/compile: devirtualization of interface calls with type assertions #64824

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mateusz834 opened this issue Dec 20, 2023 · 5 comments
Open

cmd/compile: devirtualization of interface calls with type assertions #64824

mateusz834 opened this issue Dec 20, 2023 · 5 comments
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@mdempsky
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compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
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Backlog

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@mateusz834
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Consider:

h := sha256.New() // escapes to heap
h.(encoding.BinaryUnmarshaler).UnmarshalBinary(d) // not devirtualized
h.Write(d) // devirtualized

https://go.dev/play/p/JYPsrebi5Z5

h escapes to heap, because the compiler does not take the opportunity to devirtualize the UnmarshalBinary call.

Same thing happens with even a simpler case (hash.Hash always implements io.Writer)

h := sha256.New()
h.Write(d) // devirtualized
h.(io.Writer).Write(d) // not devirtualized
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Dec 20, 2023
@mateusz834 mateusz834 added Performance NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Dec 20, 2023
@mateusz834 mateusz834 added this to the Backlog milestone Dec 20, 2023
@thanm
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thanm commented Dec 20, 2023

@mdempsky

@smiletrl
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h.(encoding.BinaryUnmarshaler).UnmarshalBinary(d) // not devirtualized
h.(io.Writer).Write(d) // not devirtualized

It seems to me that encoding.BinaryUnmarshaler and io.Writer are not concrete types, which is why they are not devirtualized ^

@mateusz834
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It seems to me that encoding.BinaryUnmarshaler and io.Writer are not concrete types

This is the whole point of of devirtualization. Same h := sha256.New() is also an interface and h.Write() call is devirtualized.

@mdempsky mdempsky self-assigned this Dec 24, 2023
@mdempsky
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This seems doable for Go 1.23. Did this come up in real world code though? For example, h.(io.Writer).Write seems unrealistic when you can just write h.Write.

@mateusz834
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mateusz834 commented Dec 24, 2023 •
edited

Did this come up in real world code though?

Only the first example, but this is not performance related in my case, I just was curious why the hash escaped and it turned out to this.

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@mdempsky mdempsky

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compiler/runtime Issues related to the Go compiler and/or runtime. FeatureRequest NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. Performance
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Go Compiler / Runtime
Status: Todo
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Backlog
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@mdempsky @mknyszek @smiletrl @gopherbot @thanm @mateusz834