Comment by tialaramex
1 day ago
Certainly compiler developers are only human, and many of them write C++ so they're humans working with a terrible programming language, I wouldn't sign up for that either (I have written small contributions to compilers, but not in C++). I still don't see "any excuses". I see more usual human laziness and incompetence, LLVM for example IMNSHO doesn't work hard enough to ensure their IR has coherent semantics and to deliver on those semantics.
The compiler bug I'm most closely following, and which I suspect you have your eye on too is: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119472 aka https://github.com/rust-lang/rust/issues/107975 https://github.com/llvm/llvm-project/issues/45725
But it seems like it's just that everybody fucked this up in similar ways, that's two different major compiler backends! I wouldn't be surprised if Microsoft (whose code we can't see) find that they don't get this quite right either.
I do not imply bad intentions, but I see the arguments brought forward in WG14. It got better in recent years but we had to push back against some rather absurd interpretations of the standard, e.g. that unspecified values can change after they are selected. Your example shows something else, the standard is simply not seemed to be very important. The standard is perfectly clear how pointer comparison works, and yet this is not alone reason enough to invest resources into fixing this if this is not shown to cause actual problems in real code.
> [... absurd interpretations] unspecified values can change after they are selected
It seems hard to not have this without imputing a freeze semantic which would be expensive on today's systems. Maybe I don't understand what you mean ? Rust considered insisting on the freeze semantic and was brought up short by the cost as I understand it.
I do not see how this adds a substantial cost and it is required for C programs to work correctly and the C standard carefully describes the exact situation where unspecified values are chosen - so the idea that the compiler is then free to break this is clearly in contradiction to the wording. Clang got this wrong and I assume mostly fixed it, because non-frozen values caused a lot inconsistency and other bugs.
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