[Index] Only hash Decl once when generating the hash value for a record
#10846
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@swift-ci Please test llvm |
| // declaration. The declaration IDs serialized above is always greater than | ||
| // zero, so there is no ambiguity between newly serialized decls and the | ||
| // serialization of declaration IDs. | ||
| HashBuilder.add(0); |
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Doesn't really matter, but is this actually needed 🤔?
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I couldn’t convince myself that there is no chance that two hashes look the same even though the values that went into them weren’t, ie. if the declaration ID matches the first character of the serialized declaration and things from there … just happen to line up – this just eliminates the possibility. I guess it doesn’t really matter because this is just a hash anyway and we can’t rule out conflicts anyway, but maybe better to be safe here.
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That seems exceedingly unlikely to me as we end up adding the type with a # in first. But 🤷 Happy to keep if you really want it
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I removed it. Saves a little bit of work, it’s unlikely that we get this sort of conflict and since we’re hashing, we technically don’t have a guarantee about conflict-freeness anyway.
| /// process runs. | ||
| /// | ||
| /// See `hashDecl` for its use. | ||
| std::map<const Decl *, size_t> HashedDecls; |
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Any reason not to use a DenseMap here?
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No, nothing particular. Probably just a result of my various iterations of this PR. Changed it to a DenseMap.
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@swift-ci Please test llvm |
…cord Say we are indexing the header file containing `NSArray`. Almost every declaration in here has a relation to `NSArray` (mostly child-of relations). This means that for every of those declarations we hash `NSArray` again by creating a `DeclHashVisitor` that, among others, adds the string `NSArray` to the hash builder. To avoid this, keep track of all the declarations that we have already incorporated into the hash. If we did already hash the declaration, only incorporate an integer into the hash.
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@swift-ci Please test llvm |
Say we are indexing the header file containing
NSArray. Almost every declaration in here has a relation toNSArray(mostly child-of relations). This means that for every of those declarations we hashNSArrayagain by creating aDeclHashVisitorthat, among others, adds the stringNSArrayto the hash builder.To avoid this, keep track of all the declarations that we have already incorporated into the hash. If we did already hash the declaration, only incorporate an integer into the hash.
This reduces the overhead of index-while-building by 16% (3.58% overhead to 3.00% overhead), based on a single test project.