On Mon, Jun 4, 2012 at 7:20 PM, Eric Botcazou <ebotca...@adacore.com> wrote: >> The code for the case in Ada is this: >> >> /* Ada doesn't feature Fortran-like COMMON variables so we shouldn't >> try to fiddle with DECL_COMMON. However, on platforms that don't >> support global BSS sections, uninitialized global variables would >> go in DATA instead, thus increasing the size of the executable. */ >> if (!flag_no_common >> && TREE_CODE (var_decl) == VAR_DECL >> && TREE_PUBLIC (var_decl) >> && !have_global_bss_p ()) >> DECL_COMMON (var_decl) = 1; >> >> That does look like premature optimization to me, but I don't really >> understand the comment, or the effect of this code. Eric, could you >> please have a look at this and help me out? > > Sure, but I don't understand what you don't understand... the comment seems > clear enough to me: DECL_COMMON is needed on some platforms if you don't want > uninitialized variables to go in DATA.
What I don't understand, is whether this is still something GNAT has to support, or whether this code can be deprecated/removed. And I ask for your help because you are one of the people who worked on this so-many-years ago (http://gcc.gnu.org/ml/gcc-patches/2004-12/msg00550.html) and because you obviously have much better understanding of GNAT and of how this kind of low-level thing works in GCC than I do. If this should continue to be supported: For the corresponding option for G++ (-fconserve-space) the documentation says that the flag isn't very useful anymore because: "This option is no longer useful on most targets, now that support has been added for putting variables into BSS without making them common." What I don't understand, is what this means for GNAT. (Remember, I help build aircraft for a living, not compilers! I can barely distinguish .bss from .data, and don't understand at all where/how GCC decides to put variables in one section or another :-D) I was hoping maybe you know how to rewrite that piece of code such that you get that uninitialized variable into BSS without DECL_COMMON. Or maybe you can tell if this code is no longer needed, so I can prepare a patch to remove it. Hope you can help, Ciao! Steven
