I'd like to ping my patch for restoring bootstrap using g++ 4.8.5 (the system compiler on RHEL 7 and later systems). https://gcc.gnu.org/pipermail/gcc-patches/2023-October/632008.html
Note the preprocessor #ifs can be removed; they are only there to document why the union u must have an explicit, empty (but not default) constructor. I completely agree with the various opinions that we might consider upgrading the minimum host compiler for many good reasons (Ada, D, newer C++ features etc.). It's inevitable that older compilers and systems can't be supported indefinitely. Having said that I don't think that this unintentional trivial breakage, that has a safe one-line work around is sufficient cause (or non-neglible risk or support burden), to inconvenice a large number of GCC users (the impact/disruption to cfarm has already been mentioned). Interestingly, "scl enable devtoolset-XX" to use a newer host compiler, v10 or v11, results in a significant increase (100+) in unexpected failures I see during mainline regression testing using "make -k check" (on RedHat 7.9). (Older) system compilers, despite their flaws, are selected for their (overall) stability and maturity. If another patch/change hits the compiler next week that reasonably means that 4.8.5 can no longer be supported, so be it, but its an annoying (and unnecessary?) inconvenience in the meantime. Perhaps we should file a Bugzilla PR indicating that the documentation and release notes need updating, if my fix isn't considered acceptable? Why this patch is an trigger issue (that requires significant discussion and deliberation) is somewhat of a mystery. Thanks in advance. Roger > -----Original Message----- > From: Jeff Law <jeffreya...@gmail.com> > Sent: 07 October 2023 17:20 > To: Roger Sayle <ro...@nextmovesoftware.com>; gcc-patches@gcc.gnu.org > Cc: 'Richard Sandiford' <richard.sandif...@arm.com> > Subject: Re: [PATCH] Support g++ 4.8 as a host compiler. > > > > On 10/4/23 16:19, Roger Sayle wrote: > > > > The recent patch to remove poly_int_pod triggers a bug in g++ 4.8.5's > > C++ 11 support which mistakenly believes poly_uint16 has a non-trivial > > constructor. This in turn prohibits it from being used as a member in > > a union (rtxunion) that constructed statically, resulting in a (fatal) > > error during stage 1. A workaround is to add an explicit constructor > > to the problematic union, which allows mainline to be bootstrapped > > with the system compiler on older RedHat 7 systems. > > > > This patch has been tested on x86_64-pc-linux-gnu where it allows a > > bootstrap to complete when using g++ 4.8.5 as the host compiler. > > Ok for mainline? > > > > > > 2023-10-04 Roger Sayle <ro...@nextmovesoftware.com> > > > > gcc/ChangeLog > > * rtl.h (rtx_def::u): Add explicit constructor to workaround > > issue using g++ 4.8 as a host compiler. > I think the bigger question is whether or not we're going to step forward on > the > minimum build requirements. > > My recollection was we settled on gcc-4.8 for the benefit of RHEL 7 and > Centos 7 > which are rapidly approaching EOL (June 2024). > > I would certainly support stepping forward to a more modern compiler for the > build requirements, which might make this patch obsolete. > > Jeff
