Add forward-mode AD support for std::thread. - #1891
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Add custom pushforwards in STLBuiltins.h and forward-mode tests.
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clang-tidy review says "All clean, LGTM! 👍" |
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Pull request overview
Adds forward-mode (pushforward) custom-derivative coverage needed for std::thread-based code paths to compile under Clad, and introduces/extends forward-mode tests around concurrency patterns using std::reference_wrapper and std::thread. Also tightens copyability detection and updates forward-mode constructor handling to move out non-copyable ValueAndPushforward results.
Changes:
- Add forward-mode custom derivatives for
std::threadconstruction and basic member ops (join,joinable) inSTLBuiltins.h. - Generalize copyability detection (
isCopyable) to treat deleted/inaccessible copy ctors as non-copyable. - Update forward-mode constructor handling to
std::movenon-copyablevalue/pushforwardmembers out of custom-derivative constructor returns. - Add/extend
ForwardMode/Concurrency.Ctests coveringreference_wrapperandstd::threadusage.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| test/ForwardMode/Concurrency.C | Adds forward-mode tests exercising reference_wrapper and std::thread constructs. |
| lib/Differentiator/CladUtils.cpp | Expands isCopyable to detect inaccessible/deleted copy constructors. |
| lib/Differentiator/BaseForwardModeVisitor.cpp | Moves non-copyable constructor pushforward results to avoid copy attempts. |
| include/clad/Differentiator/STLBuiltins.h | Introduces std::thread pushforwards and additional reference_wrapper pushforwards. |
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clang-tidy review says "All clean, LGTM! 👍" |
| if (!clonedArgs.empty() && !derivedArgs.empty()) { | ||
| QualType recTy = CE->getType().getNonReferenceType().getCanonicalType(); | ||
| if (const auto* RD = recTy->getAsCXXRecordDecl()) { | ||
| if (RD->getName() == "thread" && RD->isInStdNamespace() && |
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Why do we have to special case here?
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Constructing std::thread doesn’t call the callable, so VisitCallExpr never nest-diffs it. The callable’s tangent is just {}/nullptr, not F_pushforward, which the custom derivative needs to run AD through the worker. We can generalize this later if you prefer.
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Generalize isCopyable to detect deleted copy constructors so non-copyable return values from custom constructor pushforwards use std::move.
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clang-tidy review says "All clean, LGTM! 👍" |
Adds forward-mode custom derivatives for
std::thread(constructors, join, joinable, detach) and extendsForwardMode/Concurrency.C. The worker runs the callable’s pushforward so mutations throughstd::refupdate derivatives (free functions and named functors; lambdas not yet supported). Also generalizesisCopyableand usesstd::movefor non-copyable custom constructor pushforward returns so differentiated code compiles.