[embedded] Support _findStringSwitchCaseWithCache in Embedded Swift #78915
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kubamracek
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MaxDesiatov,
phausler,
rauhul,
zoecarver and
eeckstein
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@swift-ci please test |
eeckstein
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Jan 27, 2025
| @@ -1929,7 +1929,11 @@ OptionalBridgedFunction BridgedPassContext::lookupStdlibFunction(BridgedStringRe | |||
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| SILDeclRef declRef(decl, SILDeclRef::Kind::Func); | |||
| SILOptFunctionBuilder funcBuilder(*invocation->getTransform()); | |||
| return {funcBuilder.getOrCreateFunction(SILLocation(decl), declRef, NotForDefinition)}; | |||
| SILFunction *function = funcBuilder.getOrCreateFunction(SILLocation(decl), declRef, NotForDefinition); | |||
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It's not good to hide such kind of logic in a bridging function.
Instead it's better to explicitly call Context.loadFunction at the call site (in the optimize function in this case).
| let f = context.lookupStdlibFunction(name: "_findStringSwitchCaseWithCache") { | ||
| worklist.pushIfNotVisited(f) | ||
| } | ||
| } |
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This is a reasonable approach
…CaseWithCache in MPO instead
…y DFE, let late DFE collect it if unused
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ObjectOutliner has an optimization that replaces calls to findStringSwitchCase with _findStringSwitchCaseWithCache. This currently causes a "missing symbol" linker error in Embedded Swift, because this replacement happens without loading the body of the function from the stdlib. See the attached testcase that shows the problem (only happens under -O).
This PR fixes that with two changes:
(1) Calling lookupStdlibFunction under Embedded Swift now triggers loading the body (deserialization) + its dependencies.
(2) The above alone is not a full fix, because ObjectOutliner is a late SIL optimization, and so deserializing stdlib code causes un-specialized code to get added to the module, causing later problems (we don't expect any unspecialized code to be used in Embedded Swift after MandatoryPerformanceOptimizations are run). To fix that, we eagerly link in _findStringSwitchCaseWithCache whenever findStringSwitchCase is present as part of MandatoryPerformanceOptimizations.
Suggestions for a better approach are welcome :)
rdar://143587257