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Fix two issues related with emission of differentiability witnesses #80983

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Fix two issues related with emission of differentiability witnesses #80983

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@asl asl commented Apr 22, 2025

  1. When differentiable nested function (closure) is specialized by capture promotion pass ensure we generate a differentiability witness for the specialized function as well. Ensure the original witness is removed if the original function becomes dead.
  2. Differentiability witnesses for a function could originate either from its @differentiable attribute or from explicit @derivative(of:) attribute on the derivative. In the latter case the derivative itself might not be emitted, while original function is (e.g. original function is @inlineable, but derivative is @usableFromInline). Previously both cases were handled only when function body was emitted. As a result we missed witness in the aforementioned case. Ensure the differentiability witness originating from @derivative(of:) is emitted even if we're not going to emit body of the derivative.

Fixes #59135

asl added 4 commits April 22, 2025 09:42
@asl
Ensure we create differentiability witness when the closure is specia…
4f907bc 
…lized.

We can just re-create one with exactly same parameter and result indices
as specialization only touches capture parameters (which are always non-wrt).
@asl
Drop differentiability witnesses for dead functions for which bodies …
7dd0299 
…are erased.

This way we won't need to check if function is dead each time we canonicalize / emit code
for differentiability witnesses later on.
@asl
Emit differentiability witness originating from custom derivative dec…
f3d7f30 
…laration regardless

whether derivative body is emitted or not. This handles the cases when the function
itself if @inlinable, but the derivative is @usableFromInline, so its body it is not
emitted in the module.
@asl
Add tests
8dc69e7
@asl asl requested a review from rxwei April 22, 2025 09:36
@asl asl requested review from eeckstein and jckarter as code owners April 22, 2025 09:36
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asl commented Apr 22, 2025

@swift-ci please test

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asl commented Apr 22, 2025 •
edited
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Linux build seems to be broken due to unrelated issue:

... lib/libFoundationInternationalization.so  lib/libFoundationEssentials.so  lib/lib_FoundationCollections.a  lib/lib_FoundationCShims.a  lib/lib_FoundationICU.so  /home/build-user/build/buildbot_linux/libdispatch-linux-x86_64/libswiftDispatch.so  /home/build-user/build/buildbot_linux/libdispatch-linux-x86_64/libdispatch.so  /home/build-user/build/buildbot_linux/libdispatch-linux-x86_64/libBlocksRuntime.so  -lgcc  -lgcc_s  -lc  -lgcc  -lgcc_s && :
error: link command failed with exit code 1 (use -v to see invocation)
Sources/plutil/CMakeFiles/plutil.dir/PLUContext_KeyPaths.swift.o:main.swift.o:function $sSS6plutilE19escapedKeyPathSplitSaySSGyF: error: undefined reference to '$sSy12RegexBuilderSs11SubSequenceRtzrlE5split9separator9maxSplits25omittingEmptySubsequencesSaySsGSS_SiSbtF'

Windows too:

FAILED: bin/FoundationInternationalization.dll lib/FoundationInternationalization.lib 
C:\Windows\system32\cmd.exe /C "cd . && T:\5\bin\swiftc.exe -target x86_64-unknown-windows-msvc -j 36 -num-threads 36 -emit-library -sdk "T:/Program Files/Swift/Platforms/Windows.platform/Developer/SDKs/Windows.sdk" -gnone -Xlinker /INCREMENTAL:NO -Xlinker /OPT:REF -Xlinker /OPT:ICF -O -libc MD   -Xlinker -implib:lib\FoundationInternationalization.lib   -o bin\FoundationInternationalization.dll @CMakeFiles\FoundationInternationalization.rsp && cd ."
<unknown>:0: warning: using (deprecated) legacy driver, Swift installation does not contain swift-driver at: 'C:\Users\swift-ci\jenkins\workspace\swift-PR-windows\build\5\bin\swift-driver-new.exe'
   Creating library lib\FoundationInternationalization.lib and object lib\FoundationInternationalization.exp
ICUDateFormatter.swift.obj : error LNK2019: unresolved external symbol __imp_$sSy12RegexBuilderSs11SubSequenceRtzrlE5split9separator9maxSplits25omittingEmptySubsequencesSaySsGSS_SiSbtF referenced in function $s20FoundationEssentials4DateV0A20InternationalizationE11FormatStyleV0C15FieldCollectionV14updateScheduleAD16ICUDateFormatterC0cE4InfoV06UpdateJ0Ovg
ICUDateFormatter.swift.obj : error LNK2019: unresolved external symbol __imp_$sSS17_StringProcessing14RegexComponent0C7BuilderMc referenced in function $sS2S17_StringProcessing14RegexComponent0C7BuilderWl
Duration+UnitsFormatStyle.swift.obj : error LNK2001: unresolved external symbol __imp_$sSS17_StringProcessing14RegexComponent0C7BuilderMc

TimeZone_ICU.swift.obj : error LNK2001: unresolved external symbol __imp_$sSS17_StringProcessing14RegexComponent0C7BuilderMc

@asl asl added the AutoDiff label Apr 29, 2025
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asl commented Apr 29, 2025

@swift-ci please test

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asl commented May 2, 2025

@swift-ci please test

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@rxwei rxwei Awaiting requested review from rxwei

@eeckstein eeckstein Awaiting requested review from eeckstein eeckstein is a code owner

@jckarter jckarter Awaiting requested review from jckarter jckarter is a code owner

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[AutoDiff][SILGen] Did not create differentiability witness for function
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