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Expose function sections option #28088

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Merged
merged 2 commits into from
Jan 13, 2020
Merged

Expose function sections option #28088

merged 2 commits into from
Jan 13, 2020

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asuhan
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@asuhan asuhan commented Nov 5, 2019 •
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Add an option to generate an ELF section for each function, similar to the -ffunction-sections in Clang. In conjunction with the section elimination feature in the linker, this helps reducing the binary size for applications. This is especially helpful when an application only uses a small fraction of the Swift standard library and links it statically (the standard library needs be built with -Xfrontend -function-sections in that case).

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asuhan commented Nov 5, 2019

This is inspired from Alan Dragomirecký's https://github.com/swift-embedded/swift, which is focused on microcontrollers and is a lot more aggressive. I'm aiming for a safe, small subset of that which still results in significant wins and follow-up with additional changes to reap a lot more benefits.

@asuhan asuhan requested a review from beccadax November 5, 2019 20:53
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@asuhan asuhan force-pushed the asuhan/size_reduction branch from d7df7a1 to fcd2c57 Compare November 5, 2019 21:27
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test/LinkerSections/function_sections.swift
@@ -0,0 +1,10 @@
// REQUIRES: OS=linux-gnu || OS=linux-androideabi || OS=linux-android || OS=freebsd
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Can we use %target-object-format and compare it to ELF instead?

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Not in the REQUIRES directive:

ValueError: couldn't parse text: '%target-object-format=elf'
in expression: '%target-object-format=elf'
in REQUIRES: directive on test line 1

If there is another way to limit it to ELF, that'd be cool.

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That is rather unfortunate. Out of curiosity, what happens if you use -function-sections on MachO or PE/COFF? I'm wondering if we should actually prevent that in the driver. Apple's usage of MachO actually uses .subsections_via_symbols which means that everything is atomized and you effectively are doing -function-sections, and PE/COFF's symbol resolution is pretty close to this already.

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I don't have easy access to the other platforms. Also, is the linker / the map file format the same, at this point?

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The linker map is linker dependent unfortunately.

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asuhan commented Nov 6, 2019

@swift-ci please smoke test

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compnerd commented Nov 6, 2019

@swift-ci please test

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swift-ci commented Nov 6, 2019

Build failed
Swift Test Linux Platform
Git Sha - d7df7a1e9f511be18d68a7878ef93be51b16d5cf

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swift-ci commented Nov 6, 2019

Build failed
Swift Test OS X Platform
Git Sha - d7df7a1e9f511be18d68a7878ef93be51b16d5cf

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beccadax commented Nov 8, 2019

I honestly don't know enough to know if this is a good idea, so I'll tag a reviewer who's more likely to.

@beccadax beccadax requested review from aschwaighofer and removed request for beccadax November 8, 2019 02:07
@asuhan asuhan force-pushed the asuhan/size_reduction branch from fcd2c57 to c26e00a Compare November 9, 2019 00:36
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asuhan commented Nov 9, 2019

@swift-ci please smoke test

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compnerd commented Nov 14, 2019 •
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@brentdax - this is a good idea; MachO sorta does this implicitly through .subsections_via_symbols. This brings the same thing to ELF. The only thing is whether we want to spell this -function-sections, or match clang with -ffunction-sections. I'm still somewhat torn on making this a driver option (a frontend option for now is good, and we should promote this to default for ELF).

@compnerd compnerd requested a review from rjmccall November 14, 2019 19:24
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@asuhan asuhan force-pushed the asuhan/size_reduction branch from c26e00a to abd0aa5 Compare November 16, 2019 05:00
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asuhan commented Nov 16, 2019

@swift-ci please smoke test

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The only thing is whether we want to spell this -function-sections, or match clang with -ffunction-sections.

Swift generally doesn't use -f prefixes on options.

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@swift-ci please test windows platform

@asuhan asuhan force-pushed the asuhan/size_reduction branch from abd0aa5 to 10c620d Compare December 16, 2019 23:18
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asuhan commented Dec 16, 2019

@swift-ci please test windows platform

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@swift-ci please test Windows platform

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@swift-ci please test Windows platform

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asuhan commented Dec 18, 2019

@swift-ci please clean test Windows platform

@asuhan asuhan force-pushed the asuhan/size_reduction branch from 10c620d to dbc50fb Compare January 3, 2020 18:19
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asuhan commented Jan 3, 2020

@swift-ci please clean test Windows platform

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compnerd commented Jan 6, 2020

@swift-ci please test

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compnerd commented Jan 6, 2020

@swift-ci please clean test Windows platform

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compnerd commented Jan 6, 2020

@swift-ci please test Windows platform

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swift-ci commented Jan 6, 2020

Build failed
Swift Test OS X Platform
Git Sha - dbc50fb8171666636847387a6aa24169442b3999

@asuhan asuhan force-pushed the asuhan/size_reduction branch 3 times, most recently from daa1a1d to 05815d1 Compare January 7, 2020 00:33
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asuhan commented Jan 7, 2020

@swift-ci please test

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compnerd commented Jan 7, 2020

@swift-ci please test

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compnerd commented Jan 7, 2020

@swift-ci please test Windows platform

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swift-ci commented Jan 7, 2020

Build failed
Swift Test OS X Platform
Git Sha - 05815d13440aecf5ef07c0da70e60dabd73dfb10

@asuhan asuhan force-pushed the asuhan/size_reduction branch from 05815d1 to a210fb7 Compare January 8, 2020 00:55
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asuhan commented Jan 8, 2020

@swift-ci please test

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compnerd commented Jan 8, 2020

@swift-ci please test

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compnerd commented Jan 8, 2020

@swift-ci please test Windows platform

@asuhan asuhan force-pushed the asuhan/size_reduction branch from a210fb7 to f07de92 Compare January 9, 2020 01:27
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asuhan commented Jan 9, 2020

@swift-ci please test Windows platform

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compnerd commented Jan 9, 2020

@swift-ci please test

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compnerd commented Jan 9, 2020

@swift-ci please test Windows platform

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@swift-ci please clean test windows platform

@asuhan asuhan force-pushed the asuhan/size_reduction branch from f07de92 to 1de737f Compare January 10, 2020 01:44
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@swift-ci please test

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@swift-ci please test Windows platform

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@swift-ci please clean test Windows platform

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The test that flaked on Windows is unrelated to this. Going to go ahead and merge this.

@compnerd compnerd merged commit eed6a4e into swiftlang:master Jan 13, 2020
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@asuhan @compnerd @swift-ci @beccadax @rjmccall