[cfe-dev] [LLVMdev] Instrumenting the run-time sizes of SmallVector et al.

David Blaikie dblaikie at gmail.com
Mon Aug 11 10:35:22 PDT 2014

Any chance of performance data as well? After finding a few bugs in
SmallVector I am rather curious how much perf SmallVector is giving us
& whether it's worth the upkeep/bugs. (it probably is - so it's more
something I've been meaning to play with in my spare time as I doubt
it'll be fruitful, so I don't expect others to work on it either
unless it sounds particularly appealing)

On Sun, Aug 10, 2014 at 7:23 PM, Hans Wennborg <hans at chromium.org> wrote:
> I've always wondered how the in-line sizes of SmallVector,
> SmallString, etc. that we use in LLVM and Clang hold up against the
> actual sizes of the containers at run-time.
> To figure this out, I added a destructor to each such class, that
> would dump the container's final size into a table that got printed at
> exit. I also added a special field, __clang_ObjectLocation, to each
> such class and hacked Clang to populate that field with the source
> location of the object's declarator each time its constructor was
> called.
> I used this instrumented compiler to build vanilla Clang and captured
> the results (attached, along with the patches I used). It looks like
> we mostly get it right, but I have patches for a few size tweaks I'd
> like to do. (The measurements were done on Clang r215325 / LLVM
> r215315).
> Cheers,
> Hans
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