On Fri, Jun 11, 2010 at 9:41 PM, Manuel López-Ibáñez <lopeziba...@gmail.com> wrote: > On 11 June 2010 20:48, Cary Coutant <ccout...@google.com> wrote: >>> But if I understand correctly, mixed LTO/non-LTO + whole-program is >>> almost never correct. So we should really emit a warning for this >>> specific combination. I think making this mistake would be quite easy >>> but hard to debug. >> >> It's not only correct, it's essential. "Whole Program" doesn't mean >> that the compiler has to see all the IR for the whole program. >> Instead, the compiler has visibility over the whole program in the >> sense that it knows what variables and functions are referenced and >> defined by the non-LTO code. Linking your program with non-LTO code is >> inescapable unless we start shipping language and system libraries as >> archives of objects compiled with -flto (and remove all assembly code >> from such libraries). >> >> The plugin interface was designed to provide this essential >> information to the compiler about all the non-LTO code; until Gnu ld >> implements this or the collect2 interface provides something similar, >> you're simply working with an incomplete implementation, and you'll >> have to live with the limitations. > > This also means that linking your program with non-LTO+whole-program > code may lead to miscompilations without any warning, which is really > bad. I don't think it is a reasonable limitation and we will get bad > press when programs start breaking for users. They won't care (and > they won't even listen) about the reasons. The conclusion will be: LTO > is broken in GCC, and just use another compiler.
Thank you for this piece of FUD. Richard.
