On 08/23/2016 08:46 AM, Richard Biener wrote: > On Mon, Aug 22, 2016 at 11:54 PM, Pedro Alves <pal...@redhat.com> wrote:
>> I believe that only stage 1 is built with -std=gnu++98 forced, and also >> stage 1 is built without -Werror, so I think you'd need to start with a >> compiler that predates support for that construct, not just one >> that predates the flip of the default. > > Uh, so we don't actually catch these errors during bootstrap with a too > recent host compiler? That's pretty bad. ... > In the end conditionally allowing C++11 code in stage2+ was a mistake > if we can't catch > this kind of issues reliably. Generally speaking, let me state my current view on the theme: The oldest compiler that people are using in practice to bootstrap gcc with is what matters in the end. Forcing -std=foo and -pedantic is useful as a proxy but it can only go so far. Routinely testing bootstrap with the oldest compiler version people are willing to support, is the only reliable check, and better yet if that is left for auto testers / buildbot. Because, even if a feature is in the standard, if compilers that people want to bootstrap gcc with don't implement it, or don't implement it correctly, then we'll find ways to work around it. That happens once in a while. On the same vein, if some code using some newer language feature that is supported as a GNU extension manages to land in the tree, and nobody trips on it for a long while, then that indicates that no one is actually building with ancient compilers anymore. That indicates that we should be able to start using the feature and bump the minimum bootstrapping compiler in the documentation. >From that angle, forcing pedantic errors is a little counter productive, as it may be imposing an artificial barrier, leading to a glacier pace of newer language feature adoption in the compiler itself. E.g., what if all of gcc/clang/foo/bar have been supporting some language/library feature for a decade, as an extension? Why restrict usage of the feature? That said, I don't know when was support for the construct first added, and this patch hasn't landed yet. Support for it probably postdates gcc 4.3 and your autotesters would likely catch it (and you'd probably be annoyed). > So should we change config/warnings.m4:ACX_PROG_CXX_WARNING_ALMOST_PEDANTIC > to use -pedantic-errors? That might well be the best proxy available, but others will know better whether that is likely to cause fallout. Thanks, Pedro Alves
