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gcc4.8 outperforming gcc5, gcc6, gcc7
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Dann Corbit



Joined: 08 Mar 2006
Posts: 8052
Location: Redmond, WA USA

PostPost subject: Re: gcc4.8 outperforming gcc5, gcc6, gcc7    Posted: Tue Nov 28, 2017 6:15 pm Reply to topic Reply with quote

AndrewGrant wrote:
Final question. GCC or G++?

Both.
Quote:


I tried doing a PGO build, and actually got a different bench... which really confuses me.


I guess that you have undefined behavior in your code.
My recommendation is to use both GCC and CLANG with warnings turned up to crazy maximum and examine each and every one. (Expect thousands).

Now, I assume by bench you mean something that should be reproducible like perft or perhaps a single threaded search. I would not expect a multi-threaded search to give the same result even on the same machine and binary when repeated. It is possible for a somewhat different single threaded bench on a search to be correct. What I mean is that the code is slightly different with things like inlining instead of function calls. Most of the time these changes make no difference. If you have floating point anywhere in your program, that can do all kinds of whacky things. For instance, the total of a long column of floating point numbers which vary greatly in size will be different if you sum them forward or backwards and different again if you sort them first. Even using Kahan's adder won't completely fix that sort of thing. It only reduces the effect.


What exactly does your bench do?
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Subject Author Date/Time
gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Sun Nov 26, 2017 7:08 am
      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Lucas Braesch Sun Nov 26, 2017 7:32 am
      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Richard Delorme Sun Nov 26, 2017 8:52 am
            Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Sun Nov 26, 2017 7:02 pm
      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Sven Schüle Sun Nov 26, 2017 10:13 am
            Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Martin Sedlak Sun Nov 26, 2017 12:27 pm
            Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Sun Nov 26, 2017 6:28 pm
                  Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Sun Nov 26, 2017 6:31 pm
                        Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Sun Nov 26, 2017 7:15 pm
      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Mehdi Amini Sun Nov 26, 2017 3:10 pm
            Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Sun Nov 26, 2017 3:19 pm
                  Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Dennis Sceviour Sun Nov 26, 2017 6:13 pm
                        Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Sun Nov 26, 2017 6:36 pm
                  Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Rasmus Althoff Sun Nov 26, 2017 9:16 pm
      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Dann Corbit Tue Nov 28, 2017 3:08 am
            Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 3:55 pm
                  Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Dann Corbit Tue Nov 28, 2017 4:39 pm
                        Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 5:14 pm
                              Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Dann Corbit Tue Nov 28, 2017 6:15 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 6:28 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Rasmus Althoff Tue Nov 28, 2017 6:40 pm
                              Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Richard Delorme Tue Nov 28, 2017 6:48 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 6:52 pm
                                          Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Richard Delorme Tue Nov 28, 2017 6:58 pm
                                                Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 7:01 pm
                                                      Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 7:25 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Rasmus Althoff Tue Nov 28, 2017 6:58 pm
                                          Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Richard Delorme Tue Nov 28, 2017 7:03 pm
                                                Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Tue Nov 28, 2017 7:21 pm
                              Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Tue Nov 28, 2017 7:29 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 7:32 pm
                                          Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Rasmus Althoff Tue Nov 28, 2017 7:36 pm
                                          Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Dann Corbit Wed Nov 29, 2017 3:55 pm
                                    Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Andrew Grant Tue Nov 28, 2017 11:21 pm
                                          Re: gcc4.8 outperforming gcc5, gcc6, gcc7 Ronald de Man Wed Nov 29, 2017 12:09 am
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