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joining a lazy map of Strings is super-slow #62258

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dabrahams opened this issue Nov 26, 2022 · 1 comment
Open

joining a lazy map of Strings is super-slow #62258

dabrahams opened this issue Nov 26, 2022 · 1 comment
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. performance standard library Area: Standard library umbrella

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@dabrahams
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Description
This godbolt shows that performance goes off a cliff when we join a lazy map of Strings.

Environment

  • Swift 5.7
@dabrahams dabrahams added bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. performance standard library Area: Standard library umbrella SILOptimizer Area → compiler: SIL optimization passes labels Nov 26, 2022
@dabrahams
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dabrahams commented Nov 26, 2022 •
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And this godbolt demonstrates that most of the slowdown is due to the supposed optimization the library makes of assuming all the strings to be joined have length 1. Perhaps what is chosen for benchmarking could use some attention.

@dabrahams dabrahams mentioned this issue Nov 26, 2022
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@AnthonyLatsis AnthonyLatsis added compiler The Swift compiler itself and removed compiler The Swift compiler itself labels Nov 26, 2022
@dabrahams dabrahams removed the SILOptimizer Area → compiler: SIL optimization passes label Nov 26, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. performance standard library Area: Standard library umbrella
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@dabrahams @AnthonyLatsis