On Mon, Aug 1, 2011 at 8:43 PM, Oleg Smolsky <oleg.smol...@riverbed.com> wrote: > On 2011/7/29 14:07, Xinliang David Li wrote: >> >> Profiling tools are your best friend here. If you don't have access to >> any, the least you can do is to build the program with -pg option and >> use gprof tool to find out differences. > > The test suite has a bunch of very basic C++ tests that are executed an > enormous number of times. I've built one with the obvious performance > degradation and attached the source, output and reports. > > Here are some highlights: > v4.1: Total absolute time for int8_t constant folding: 30.42 sec > v4.6: Total absolute time for int8_t constant folding: 43.32 sec > > Every one of the tests in this section had degraded... the first half more > than the second. I am not sure how much further I can take this - the > benchmarked code is very short and plain. I can post disassembly for one > (some?) of them if anyone is willing to take a look...
I have a hard time actually seeing what expressions they try to fold (argh, templates everywhere ...). One thing that changed between 4.1 and 4.6 is that we can no longer re-associate freely signed integers because of undefined overflow concerns - which is a correctness issue. Depending on the way the tests are written the folding in 4.1 was probably a bug. Richard. > Thanks, > Oleg. >
