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Patch Out a Source of Iterator Invalidation

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Synthesized file units were designed for autodiff to emit synthesized declarations, and also to sidestep the design implications of doing so late in the compiler pipeline.

A call to materialize synthesized file units was added to the GetImplicitSendable request. This introduced a source of iterator invalidation into forEachFileToTypeCheck in whole-module builds. Any call to insert a new file into the module has the potential to cause the underlying SmallVector to reallocate.

This patch provides a narrow workaround that stops using iterators altogether in forEachFileToTypeCheck. However, this bug reveals a severe architectural flaw in the concept of a synthesized file unit. Iterating over the files in a module is an extremely common operation, and there now are myriad ways we could wind up calling a function that mutates the module's list of files in the process. This also means the number and kind of files being visited by compiler analyses is dependent upon whether a request that inserts these files has or has not been called.

This suggests the call to ModuleDecl::addFile in FileUnit::getOrCreateSynthesizedFile is deleterious and should be removed. Doing so will come as part of a larger refactoring.

rdar://94043340
This commit is contained in:
Robert Widmann
2022-05-28 12:06:42 -07:00
parent e9fb9091b8
commit bbe4608fa4
3 changed files with 22 additions and 2 deletions
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9
lib/AST/Module.cpp
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@@ -3064,6 +3064,15 @@ SynthesizedFileUnit &FileUnit::getOrCreateSynthesizedFile() {
return *thisSynth;
SynthesizedFile = new (getASTContext()) SynthesizedFileUnit(*this);
SynthesizedFileAndKind.setPointer(SynthesizedFile);
// FIXME: Mutating the module in-flight is not a good idea. Any
// callers above us in the stack that are iterating over
// the module's files will have their iterators invalidated. There's
// a strong chance that whatever analysis led to this function being
// called is doing just that!
//
// Instead we ought to just call ModuleDecl::clearLookupCache() here
// and patch out the places looking for synthesized files hanging off of
// source files.
getParentModule()->addFile(*SynthesizedFile);
}
return *SynthesizedFile;