[llvm] r212816 - raw_svector_ostream: grow and reserve atomically
alp at nuanti.com
Fri Jul 11 11:31:42 PDT 2014
On 11/07/2014 19:45, Chandler Carruth wrote:
> On Fri, Jul 11, 2014 at 7:02 AM, Alp Toker <alp at nuanti.com
> <mailto:alp at nuanti.com>> wrote:
> Author: alp
> Date: Fri Jul 11 09:02:04 2014
> New Revision: 212816
> URL: http://llvm.org/viewvc/llvm-project?rev=212816&view=rev
> raw_svector_ostream: grow and reserve atomically
> Including the scratch buffer size in the initial reservation
> eliminates the
> subsequent malloc+move operation and offers a healthier constant
> growth with
> less memory wastage.
> What benchmarks did you run to measure the memory waste, and what were
> the numbers? I think it is really important to provide these kinds of
> details with potentially performance impacting changes like this.
I've been getting some good timings with a synthetic clang syntax-only
diagnostics engine stress test (10 runs, Before: 0m3.317s After:
0m3.094s). I can't be sure this is a win for every workload so I've
boiled the commit down into a cleanup in r212837.
I'll post my thoughts shortly so we can discuss ideas to resolve that
// FIXME: Prevent resizing during this flush().
My secondary interest here is to cook up a seekable raw_svector_ostream
so we can run more of the compilation in memory / via API without file
descriptors, where raw_fd_ostream is currently required. Beware, patches
with even more new ostream subclasses are getting proposed shortly ;-)
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