4 ms·

Unfortunately, Clang is still a bit shaky at times. In our (C++) project, we get a miscompilation in Clang that we don't get with gcc, the visual studio compile

by mzl 16y ago

Unfortunately, Clang is still a bit shaky at times. In our (C++) project, we get a miscompilation in Clang that we don't get with gcc, the visual studio compiler, nor the intel compiler. It will be great when it is more stable: clang cuts the compile time by half in comparison with gcc (from 18 minutes to 9 minutes on my computer).

X-Istence 16y ago
File a bug report. They are very receptive of them. Especially if you get a miscompilation.
- mzl 16y ago
  I hope to do so, I really like the project and want it to succeed. Unfortunately, I'm not yet sure how to reduce the 100000 lines to something manageable with the problem clear :)
  - sparky 16y ago
    Do you suspect the bug to be in clang (the front-end) itself, or in LLVM's optimizer or back-end? For the latter cases, bugpoint is included in the LLVM source tree and does a good job of narrowing things down, so long as you provide a program whose output should be deterministic (this may involve some work on your part if your program usually depends on data from the outside world). It is described here http://llvm.org/docs/Bugpoint.html http://llvm.org/docs/Bugpoint.html . It may be useful for Clang bugs too, I'm not sure. People may help you by suggesting strategies for finding a small test case that tickles the same problem if you post to the mailing list here http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev . I've posted a couple times and found people surprisingly responsive and helpful.
    - mzl 16y ago
      That looks like an interesting tool, I'll have to try it out. The program is deterministic given a fixed seed. The bug depends on whether or not optimization is on, so it might be in the backend. What I've heard is that the C++ FE in particular still does have some troubles with miscompilations, so that is why I suspect it.
chc 16y ago
Clang is really good at C and Objective-C. C++ is kind of its weak point, most likely because C++ is a couple of orders of magnitude more complex than either of those languages.
- mzl 16y ago
  I was actually surprised that it could compile our stuff at all, and that it runs mostly all right. We do use a lot of the language, and we need at least gcc version 4.2 for example.
wash 16y ago
I do a lot of C++ template metaprogramming, so I end up running into 3-5 Clang internal compiler errors (In my circles, "ICE"s) a week, if not more. With GCC I maybe run into 3-5 a month. The difference is that I can pinpoint the error. Clang dies gracefully, with a stack trace, source file location, and, for parse errors, the tokens that are currently being parsed. The problem might not always be easy to fix, but I never have to waste time trying to find it. If you want a more stable Clang, then build one. ;)

by mzl 16y ago

X-Istence 16y ago

File a bug report. They are very receptive of them. Especially if you get a miscompilation.

mzl 16y ago
I hope to do so, I really like the project and want it to succeed. Unfortunately, I'm not yet sure how to reduce the 100000 lines to something manageable with the problem clear :)
- sparky 16y ago
  Do you suspect the bug to be in clang (the front-end) itself, or in LLVM's optimizer or back-end? For the latter cases, bugpoint is included in the LLVM source tree and does a good job of narrowing things down, so long as you provide a program whose output should be deterministic (this may involve some work on your part if your program usually depends on data from the outside world). It is described here http://llvm.org/docs/Bugpoint.html http://llvm.org/docs/Bugpoint.html . It may be useful for Clang bugs too, I'm not sure. People may help you by suggesting strategies for finding a small test case that tickles the same problem if you post to the mailing list here http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev . I've posted a couple times and found people surprisingly responsive and helpful.
  - mzl 16y ago
    That looks like an interesting tool, I'll have to try it out. The program is deterministic given a fixed seed. The bug depends on whether or not optimization is on, so it might be in the backend. What I've heard is that the C++ FE in particular still does have some troubles with miscompilations, so that is why I suspect it.

chc 16y ago

Clang is really good at C and Objective-C. C++ is kind of its weak point, most likely because C++ is a couple of orders of magnitude more complex than either of those languages.

mzl 16y ago
I was actually surprised that it could compile our stuff at all, and that it runs mostly all right. We do use a lot of the language, and we need at least gcc version 4.2 for example.

wash 16y ago

I do a lot of C++ template metaprogramming, so I end up running into 3-5 Clang internal compiler errors (In my circles, "ICE"s) a week, if not more. With GCC I maybe run into 3-5 a month. The difference is that I can pinpoint the error. Clang dies gracefully, with a stack trace, source file location, and, for parse errors, the tokens that are currently being parsed. The problem might not always be easy to fix, but I never have to waste time trying to find it. If you want a more stable Clang, then build one. ;)