On Thu, May 11, 2017 at 12:43 PM, Jakub Jelinek <ja...@redhat.com> wrote: > On Thu, May 11, 2017 at 11:06:13AM +0100, Jonathan Wakely wrote: >> It's absolutely a supported feature. Why else do you think the manual >> would discuss so many options for preprocessing, and options for >> compiling preprocessed code? >> https://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html seems quite >> explicit. >> >> > Also, has anyone seen/heard of any real-world issues with compiling >> > preprocessed source code? >> >> There are very occasional bugs where compiling the original source >> code behaves slightly differently, e.g. regarding what is considered a >> system header, but it usually only affects warnings or errors, not >> code generation. And nothing that would mean separate preprocessing >> and compilation shouldn't be relied on. > > Especially in recent GCC versions the amount of differences for warnings and > errors keeps dramatically increasing, with separate preprocessing simply > too much information is lost (macro contexts, lint style comments, exact > locations, system header issues, ...). > > So it is far better to not use -E, but instead -E -fdirectives-only > for the preprocessing step, which will get you also single file with all the > includes in it, but macros, comments etc. are still in there. > > Tried to explain that to the ccache people, but they aren't listening.
For the very same reason -g3 debuginfo is also not what you expect (all macros are gone). Richard. > Jakub
