On 5/10/20, Eric Gallager <eg...@gwmail.gwu.edu> wrote: > On 1/10/20, Jason Merrill <ja...@redhat.com> wrote: >> Back in 2009 Manuel sent a patch to avoid useless -Wconversion warnings >> on compound assignment of types that get promoted to int: >> >> https://gcc.gnu.org/ml/gcc-patches/2009-08/msg00582.html >> >> Joseph argued that those warnings are sometimes useful, and that they >> should be controlled by a separate flag. So this patch introduces >> -Warith-conversion, which is off by default in this patch. >> >> Joseph, is that default OK with you? If not, can you explain your >> reasoning more about why the warnings are desirable? It seems to me >> that even in cases where you don't know the ranges involved, it's wrong >> for e.g. 'mychar += 1' to warn when 'myint += 1' doesn't. In both >> cases, the addition might overflow the range of the target type, but >> that isn't about the conversion; the result is the same as if the >> operation had been done in the operand/target type rather than the >> promoted type. >> >> The change to cp/typeck.c is a placeholder to use if the default setting >> changes; even if we end up warning by default for mychar = mychar + 1, I >> really don't want to warn about mychar += 1. >> >> sign.diff is a prerequisite tidying that moves the warnings from >> unsafe_conversion_p back into conversion_warning with the others. >> >> rshift.diff restores the short_shift code to the C++ front end so that C >> and C++ give the same warnings with -Warith-conversion. >> >> Tested x86_64-pc-linux-gnu. Comments? >> > > Hi Jason, thanks for this new flag. Now that GCC 10 has been released > I was checking the release notes to review everything new in GCC 10, > and I didn't see any mention of -Warith-conversion on it. Could you > add a quick note about -Warith-conversion to changes.html please? > > Thanks, > Eric >
Something just like "Some warnings that -Wconversion previously issued now also require -Warith-conversion" or something would be fine.
