No, you really don't need undefined behavior in the standard in order to enable bug-finding. The standard could've (and still could...) make signed integer overflow "implementation-defined" rather than "undefined". Compilers would thus be required to have *some documented meaning* for it (e.g. wrap 2's-complement, wrap 1's-complement, saturate to min/max, trap, or whatever...), but must not have the current "Anything goes! I can set your cat on fire if the optimizer feels like it today!" behavior. Such a change to the standard would not reduce any ability to do error checking, as compilers that want to be helpful could perfectly-well define it to trap at runtime when given certain compiler flags, and perfectly well warn you of your dependence upon unportable implementation-defined behavior (or, that your program is going to trap), at build-time. [Sending again as a plain-text email, since a bunch of mailing lists apparently hate on multipart messages that even contain a text/html part...] On Mon, Feb 29, 2016 at 2:38 PM, Lawrence Crowl via llvm-dev <llvm-dev@xxxxxxxxxxxxxx> wrote: > On 2/28/16, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> The fact is, undefined compiler behavior is never a good idea. Not for >> serious projects. > > Actually, undefined behavior is essential for serious projects, but > not for the reasons mentioned. > > If the language has no undefined behavior, then from the compiler's view, > there is no such thing as a bad program. All programs will compile and > enter functional debug (possibly after shipping to customer). On the > other hand, a language with undefined behavior makes it possible for > compilers (and their run-time support) to identify a program as wrong. > > The problem with the latest spate of compiler optimizations was not the > optimization, but the lack of warnings about exploiting undefined behavior. > > -- > Lawrence Crowl > _______________________________________________ > LLVM Developers mailing list > llvm-dev@xxxxxxxxxxxxxx > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
