mboehme added a comment. In D126061#3585681 <https://reviews.llvm.org/D126061#3585681>, @nikic wrote:
> FYI this change had a measurable effect on compile-time > (http://llvm-compile-time-tracker.com/compare.php?from=7acc88be0312c721bc082ed9934e381d297f4707&to=8c7b64b5ae2a09027c38db969a04fc9ddd0cd6bb&stat=instructions), > about 0.5% regression for `O0` builds. Not sure if that's expected. I've found the reason for this slowdown, and a fix. In a number of places, this patch adds additional local variables of type `ParsedAttributes`, typically because we need to keep track of declaration and decl-specifier-seq attributes in two separate `ParsedAttribute` lists where previously we were putting them in the same list. Note that in the vast majority of cases, these `ParsedAttributes` lists are empty. I would have assumed that creating an empty `ParsedAttributes`, potentially iterating over it, then destroying it, is cheap. However, this is not true for `ParsedAttributes` because it uses a `TinyPtrVector` as the underlying container. The same is true for the `AttributePool` that `ParsedAttributes` contains. `TinyPtrVector` is amazingly memory-frugal in that it consumes only a single pointer worth of memory if the vector contains zero or one elements. However, this comes at a cost: `begin()` and `end()` on this container are relatively expensive. As a result, iterating over an empty `TinyPtrVector` Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D126061/new/ https://reviews.llvm.org/D126061 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
