[PATCH] D79834: Speed up preamble building by replacing the slow translateFile call by a new, faster isMainFile check

[Alex Lorenz via Phabricator via cfe-commits]

arphaman added a comment.

In D79834#2034666 <https://reviews.llvm.org/D79834#2034666>, @jkorous wrote:

> IIUC the issue is that `SourceManager::translateFile()` basically consists of two blocks of code:
>
>   // First, check the main file ID, since it is common to look for a
>   // location in the main file.
>   if (MainFileID.isValid()) {
>     bool Invalid = false;
>     const SLocEntry &MainSLoc = getSLocEntry(MainFileID, &Invalid);
>     if (Invalid)
>       return FileID();
>   
>     if (MainSLoc.isFile()) {
>       const ContentCache *MainContentCache =
>           MainSLoc.getFile().getContentCache();
>       if (MainContentCache && MainContentCache->OrigEntry == SourceFile)
>         return MainFileID;
>     }
>   }
>   
>
> and
>
>     // The location we're looking for isn't in the main file; look
>     // through all of the local source locations.
>   ...
>
>
> The comments suggest that the first block is a heuristic related to our case and the second block I would assume being the expensive part. `SourceManager::getFileEntryRefForID` implementation seems similar to the first block.
>
> It makes sense to me to avoid the expensive search. I'm just wondering - how much speedup do we get with caching the value?


Good question, let me check if caching can be avoided.


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https://reviews.llvm.org/D79834