jkorous marked 5 inline comments as done.
jkorous added inline comments.
================
Comment at: clang/lib/AST/ASTContext.cpp:494
+ // Explicitly not calling ExternalSource->ReadComments() as we're not
+ // interested in those.
+ ArrayRef<RawComment *> RawComments = Comments.getComments();
----------------
gribozavr wrote:
> Would be great to explain why (because we assume that the decls and their
> comments were parsed just now). Otherwise the comment could enumerate a lot
> of other things that we are not calling here either...
Haha, you're absolutely right! Thanks.
================
Comment at: clang/lib/AST/ASTContext.cpp:584
+ // terminating early.
+ for (auto CIt = RawComments.begin(); CIt != RawComments.end(); ++CIt) {
+ RawComment *C = *CIt;
----------------
gribozavr wrote:
> Scanning all comments for every decl? Isn't that O(n^2)?
>
> Also logic duplication below. I was expecting a call to
> `getRawCommentForDeclNoCache`, with an appropriate flag to disable loading
> external comments (it is a low-level API, users generally don't call it).
The important thing is that the expensive operation is source location
decomposition. That's why I cache everything - `GetCachedCommentBegin` etc.
So while you're right that iteration-wise it's O(iteration*c*d) it`s actually
O(decompose*c + decompose*d) because of the caching. The current code (which is
sorting all the comments) is at least O(decompose*c*ln(c)) once you have more
comments than `sqrt(300)` (==`MagicCacheSize` in
`SourceManager::getInBeforeInTUCache()`).
That being said - you're right that just not-loading external comments in
`getRawCommentForDeclNoCache` definitely has it's appeal. I'm running a test
now get some idea about performance of both approaches.
BTW in theory we could also do one of these:
1. Allow clients to transparently set `MagicCacheSize` in
`SourceManager::getInBeforeInTUCache()` which is used for SourceLocation
sorting (`BeforeThanCompare<RawComment>`) is currently hard-coded to 300 while
we are comparing ~100k x ~100k locations.
2. Change caching strategies in `SourceManager::getFileID` and
`SourceManager::getLineNumber`.
Repository:
rC Clang
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D61103/new/
https://reviews.llvm.org/D61103
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