5 ms·

I'm not saying add any runtime checking, but if undefined behavior can be proven at compile time, then it should flag that instead of doing something weird.

mehrdadn 9y ago
Are you imagining Clang actually did detect it and merely didn't tell you? That seems possible but it seems more likely that it didn't.
adrianN 9y ago
That's what clang's static analyzer is for. The analysis is pretty difficult and would slow down compilation unnecessarily.
- rurban 9y ago
  No, that is what -Wall is for. Nobody runs the static analyzer, there are more people using ubsan fwiw.
  - jhasse 9y ago
    > The analysis is pretty difficult and would slow down compilation unnecessarily.
  - 2trill2spill 9y ago
    > No, that is what -Wall is for. Nobody runs the static analyzer, there are more people using ubsan fwiw. How do you know what other people are using? I personally use the clang static analyzer all the time. Also it seems like you think these options are mutually exclusive they are not.
    - rurban 9y ago
      Because I know a lot of software. Everybody uses -Wall, some -Wextra and even -pedantic, a few asan or ubsan, nobody uses clang specific analyze.
      - 2trill2spill 9y ago
        > nobody uses clang specific analyze. That's a pretty bold claim. I use it for all my C projects, FreeBSD use's it[1], Chromium uses it[2]. It seems your basing this whole claim on personal anecdotes which by definition is unreliable. [1]: https://chromium.googlesource.com/chromium/src/+/lkcr/docs/clang_static_analyzer.md https://chromium.googlesource.com/chromium/src/+/lkcr/docs/c... [2]: https://github.com/freebsd/freebsd-ci/tree/master/scan-build https://github.com/freebsd/freebsd-ci/tree/master/scan-build
        rurban 9y ago
        Which other software probes for a static analyzer? Is there a autoconf or cmake probe? FreeBSD and chromium are islands unfortunately.
  - mikeash 9y ago
    The static analyzer is extremely useful. Why aren’t people running it?
    - pjmlp 9y ago
      Because reasons. See Herb Sutter's talk at CppCon 2015. At a given moment he asks the audience if they use any kind of static analysis tools. About 1% of the audience said they were using one. Which is why everything that requires external tooling, instead of being part of the language is easily ignored.
      - mikeash 9y ago
        Would it help if the static analyzer were folded into clang itself and enabled with a flag (-Wanalyze?) rather than using a separate tool? That way it could just be a slight tweaking of build flags, and left enabled if it performs well on a given code base, rather than requiring extra work and thought.
        pjmlp 9y ago
        Well it helped when XCode came out with integrated clang static analysis, vs with the largely ignored lint.
    - cwzwarich 9y ago
      The main reason people avoid static analysis is excessive false positives.
Joky 9y ago
So to take an example, signed integer arithmetic can't overflow (or it is UB), would you like a compiler that flag for every single arithmetic operation on int when it can't prove it won't overflow? So we couldn't compile `int foo(int a, int b) { return a + b; }` right?

mehrdadn 9y ago

Are you imagining Clang actually did detect it and merely didn't tell you? That seems possible but it seems more likely that it didn't.

adrianN 9y ago

That's what clang's static analyzer is for. The analysis is pretty difficult and would slow down compilation unnecessarily.

rurban 9y ago
No, that is what -Wall is for. Nobody runs the static analyzer, there are more people using ubsan fwiw.
- jhasse 9y ago
  > The analysis is pretty difficult and would slow down compilation unnecessarily.
- 2trill2spill 9y ago
  > No, that is what -Wall is for. Nobody runs the static analyzer, there are more people using ubsan fwiw. How do you know what other people are using? I personally use the clang static analyzer all the time. Also it seems like you think these options are mutually exclusive they are not.
  - rurban 9y ago
    Because I know a lot of software. Everybody uses -Wall, some -Wextra and even -pedantic, a few asan or ubsan, nobody uses clang specific analyze.
    - 2trill2spill 9y ago
      > nobody uses clang specific analyze. That's a pretty bold claim. I use it for all my C projects, FreeBSD use's it[1], Chromium uses it[2]. It seems your basing this whole claim on personal anecdotes which by definition is unreliable. [1]: https://chromium.googlesource.com/chromium/src/+/lkcr/docs/clang_static_analyzer.md https://chromium.googlesource.com/chromium/src/+/lkcr/docs/c... [2]: https://github.com/freebsd/freebsd-ci/tree/master/scan-build https://github.com/freebsd/freebsd-ci/tree/master/scan-build
      - rurban 9y ago
        Which other software probes for a static analyzer? Is there a autoconf or cmake probe? FreeBSD and chromium are islands unfortunately.
- mikeash 9y ago
  The static analyzer is extremely useful. Why aren’t people running it?
  - pjmlp 9y ago
    Because reasons. See Herb Sutter's talk at CppCon 2015. At a given moment he asks the audience if they use any kind of static analysis tools. About 1% of the audience said they were using one. Which is why everything that requires external tooling, instead of being part of the language is easily ignored.
    - mikeash 9y ago
      Would it help if the static analyzer were folded into clang itself and enabled with a flag (-Wanalyze?) rather than using a separate tool? That way it could just be a slight tweaking of build flags, and left enabled if it performs well on a given code base, rather than requiring extra work and thought.
      - pjmlp 9y ago
        Well it helped when XCode came out with integrated clang static analysis, vs with the largely ignored lint.
  - cwzwarich 9y ago
    The main reason people avoid static analysis is excessive false positives.

Joky 9y ago

So to take an example, signed integer arithmetic can't overflow (or it is UB), would you like a compiler that flag for every single arithmetic operation on int when it can't prove it won't overflow? So we couldn't compile `int foo(int a, int b) { return a + b; }` right?