On Fri, Apr 2, 2021 at 4:32 PM Tadeus Prastowo <tadeus.prast...@unitn.it> wrote: > > Hi Arthur, > > On Fri, Apr 2, 2021 at 5:04 PM Arthur Gautier > <gcc.gnu....@superbaloo.net> wrote: > > > > Hi Tadeus, > > > > On Fri, Apr 2, 2021 at 9:07 AM Tadeus Prastowo <tadeus.prast...@unitn.it> > > wrote: [...] > > By "the manual", do you refer to > https://gcc.gnu.org/install/build.html#Building-with-profile-feedback > ? yes > > Quoting the page: > When ‘make profiledbootstrap’ is run, it will first build a stage1 compiler. > This compiler is used to build a stageprofile compiler instrumented > to collect execution counts of instruction and branch probabilities. > Training run is done by building stagetrain compiler. > Finally a stagefeedback compiler is built using the information collected. > End quote. > > Based on the quote, a reproducible build is to expected for the > following compilers: > 1. The stage1 compiler. > 2. The stageprofile compiler, which is built by the stage1 compiler. > 3. The stagetrain compiler, which is built by the stageprofile compiler. > > Then, a reproducible build is expected for the stagefeedback compiler > on the condition that the same information, which was collected by the > stageprofile compiler when building the stagegrain compiler, is used. > > Do you agree with that reasoning? Yes, and as far as I can tell, up to the stageprofile I get the same result. Only the output of the stagetrain compilation changes, which affects the stagefeedback compilation.
> > > And I would expect, given > > the same input provided in the same order, two different architectures > > to take the same branch, and not observe any difference. > > In other words, you expect that branch statistics depends only on the > given source code. Correct? That would be my understanding (although very limited). What I'm trying to understand is: what "local behavior" is injected in my build, and see if I could get rid of that, and only keep branch statistics/execution counts, which I expect to be reproducible. > > > I understand > > that with autoprofiled builds, the local architecture behavior is > > injected in the build, but I don't use that. > > I'm not using any -march in the build either (as far as I can > > understand/tell). So I do not expect the build to change its > > instruction set either. > > > > Is that normal that two different architectures would issue two > > different "execution counts of instruction and branch probabilities"? > > I guess that it would be the case. > > > Or is there something more? > > Perhaps you can have the reproducible build that you want by first > isolating the information that is collected by the stageprofile > compiler when building the stagegrain compiler and then reusing the > same information when building every other stagefeedback compiler. Yeah, but said information is not reproducible itself (that would defeat the purpose of the effort).
