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Honest question: on OS X, Apple has embraced clang and not gcc anymore. When I use linux clang is also available. Can anyone chime in about how a developer wou

Honest question: on OS X, Apple has embraced clang and not gcc anymore. When I use linux clang is also available. Can anyone chime in about how a developer would choose gcc over clang (and vice versa). I have to admit that even though I write in c++, I seldom pay attention to which compiler I would use for x vs y feature, etc. Compilers feel like a black-box to me. I don't go inside it. Edit: I don't know about Windows, I know gcc is available. I haven't looked if clang is. Edit 2: Intel also makes compilers, to which I own, but never use. I guess I feel like I am not doing anything specific to Intel

jcranmer 11y ago
gcc generally provides somewhat better code than clang, both in runtime and in object size. Clang has traditionally done better at warnings and diagnostics, although gcc has definitely closed that space in the past few years (since 4.9 or so).
- jason_slack 11y ago
  are there circumstances where a developer should compile their products with more than one compiler to flush out issues, potentially fine tune/optimize code, etc? I've never thought about doing this.
  - lallysingh 11y ago
    Yes, at least make sure that your code compiles and the tests pass on more than one. That way you're sure that you're not depending on peculiars of one compiler (their specific behaviors that are undefined in the standard, optimizer actions, etc).
    - bschwindHN 11y ago
      And a nice way to run multiple compilers easily is by using a tool like Travis CI with their compiler matrix support. https://docs.travis-ci.com/user/languages/c https://docs.travis-ci.com/user/languages/c
  - corysama 11y ago
    When I was working on multi-platform console engines, I had no choice but to compile with several highly varying compilers. It teaches you very quickly how quietly compiler-specific extensions and quirks work their way into your code. Also, different dev environments offer different tools. A nice benefit of running in lots of environments was that I often could pick between the best tools of any platform whenever I had a problem they could help solve.
  - gaius 11y ago
    At a previous job we ensured we got clean compiles with Visual C++, SPARCworks and xlc, even tho' all our customers were only actually interested in the Solaris version.
  - EliRivers 11y ago
    Yes; whenever they want to produce a higher quality product. Which I'd anticipate being "whenever possible", limited only by compiler extensions one has to use, and dev/target hardware.
  - danieltillett 11y ago
    From experience make sure you compile 32bit and 64bit versions too - this flushed out a surpring number of bugs.
  - blue11 11y ago
    I've worked at places where we maintained a dual build, VisualC++ and Linux gcc, because we wanted to be able to develop and run in multiple environments. That forces you to write clean standard-compliant code, although in some cases it could be a pain.
gravypod 11y ago
GCC, from my experience, generates much faster binaries. Clang is much faster at compiling though. It's a trade off.
- octoploid 11y ago
  Correction. Clang used to compile much faster years ago. But nowadays GCC-6 actually compiles faster than clang-3.8.0. See e.g.: http://hubicka.blogspot.com/2016/03/building-libreoffice-with-gcc-6-and-lto.html http://hubicka.blogspot.com/2016/03/building-libreoffice-wit...
- PeCaN 11y ago
  That was the case circa 2012 with Clang 3.1 and GCC 4.7, but both have closed the gaps. Clang generates code roughly as fast as GCC and GCC compiles about as fast as Clang.
  - agumonkey 11y ago
    funny how this opposite spectrum leads to https://upload.wikimedia.org/wikipedia/commons/7/7c/Vector_Addition.png https://upload.wikimedia.org/wikipedia/commons/7/7c/Vector_A... risc / cisc gathered around each other, clang / gcc... progress by antagonism
jordigh 11y ago
Different set of bugs (I know of more annoying bugs in clang and libc++ than I do of their GNU counterparts, perhaps only because I know gcc better), different performance in the generated code. Try them both and benchmark, see which you like best. I believe you can get gcc from homebrew, but beware of linking gcc-built code with libstdc++ and not libc++. http://stackoverflow.com/questions/18976922/how-to-use-the-gcc-compiler-in-the-mac-terminal-instead-of-clang http://stackoverflow.com/questions/18976922/how-to-use-the-g...
pjmlp 11y ago
There are quite a few other compilers available, if you look into commercial UNIXes, embedded and real time OSes, game consoles, HPC.
kkylin 11y ago
It also depends a little bit on your style of programming. For example, in C code, I personally like using gcc extensions like nested functions. As far as I know this is not supported by clang (but perhaps someone more knowledgeble can chime in).
- Kristine1975 11y ago
  >nested functions They are not supported. In C++11 you can use lambdas: auto const local_func = [&](...) { ... }; And then later: local_func(...);
  - CyberDildonics 11y ago
    Not only that but you can even create a struct inside a function and overload operator(). I don't know if this is possible in C++03 or not.
    - Kristine1975 11y ago
      >I don't know if this is possible in C++03 or not. It is/was. It could be used to manually create a lambda function.
      - lultimouomo 11y ago
        But note that you cannot use such class as a template parameter, as it has no linkage. Which makes it mostly useless, since you usually want to use lambdas with templates. This restriction has been lifted in C++11.
      - CyberDildonics 11y ago
        Inside of a function too?
  - kkylin 11y ago
    Cool, thanks!
brandmeyer 11y ago
Right now, clang is missing several features that I care about, but most of the industry doesn't[1]. Clang is a 90% or maybe 95% solution, and my use cases aren't covered. So I don't use it. That said, I am grateful for the competition: GCC has definitely been getting better thanks to clang. [1] Namely, -Wdouble-promotion, big-endian ARM interrupt handlers, -fstack-usage, -Og, -fno-delete-null-pointer-checks, -falign-functions
- beeforpork 11y ago
  +1 for -fno-delete-null-pointer-checks But actually, what I'd rather like is -fno-optimise-based-on-undefined-behaviour.
  - brandmeyer 11y ago
    -fno-delete-null-pointer-checks In my particular case, I'm programming in a microcontroller environment where there is ordinary RAM at the NULL address. Dereferencing NULL therefore doesn't halt the program at all.
    - teddyh 11y ago
      Your compiler, or rather your architecture definition supplied to the compiler, is broken. NULL should be an invalid pointer value — it need not actually be memory address 0. (The explicit constant 0 in a pointer context should be automatically translated by the compiler into this special invalid pointer value.) There have been several such architectures already, so this should not present an insurmountable problem.
    - yrro 11y ago
      AIUI, this code is not affected: X *foo = ...; if (foo) foo->bar(); But this code will be: X *foo = ...; foo->bar(); if (foo) { ... } Since foo is dereferenced unconditionally, the compiler is allowed to assume that it will not be null in the above code, and therefore the test on the third line to determine whether foo is null or not is useless and can be omitted.
Esau 11y ago
The one thing I hear mentioned is that GCC supports more processors than Clang does. I believe this is the reason that NetBSD and OpenBSD still use GCC.
- maaku 11y ago
  What do you mean by support more processors?
  - jlg23 11y ago
    The comment was referring to CPU architectures.
    - maaku 11y ago
      I understand that. Still, what was meant? C/C++ don't have mechanisms for automatic parallelization, or if there are obscure extensions they are not commonly used. Compilation is usually a single-processor task, with linear speedup obtained by doing multiple compilation units in parallel (make -jN). So in what way can a compiler be "better" for multi-processor / multi-core CPU architectures?
      - MereInterest 11y ago
        I believe that in this context, "more processors" meant "more different models of processors". That is, there exist processors for which gcc can produce binaries and clang cannot produce binaries.
        maaku 11y ago
        Ah ok. More backends.
        groovy2shoes 11y ago
        Well, support for more target architectures, really. I can easily imagine cases where a compiler could have multiple backends for the same target arch, so the number of backends could be misleading in that regard. For a summary from the OpenBSD perspective, see here: http://marc.info/?l=openbsd-misc&m=137530560232232&w=2 http://marc.info/?l=openbsd-misc&m=137530560232232&w=2
Kristine1975 11y ago
IIRC gcc generates somewhat faster machine code. clang is available for Windows as clang-cl from here: http://llvm.org/releases/download.html http://llvm.org/releases/download.html Here's the status page for compatibility with MSVC (clang 3.9, i.e. current development version): http://clang.llvm.org/docs/MSVCCompatibility.html http://clang.llvm.org/docs/MSVCCompatibility.html
jeffdavis 11y ago
1. License. If you are worried about GPL (especially v3), then you are better off with clang. 2. GCC is generally considered to produce better binaries. 3. Smart projects will support both and test with both. Before, even though projects tried to be portable, GCC was the only compiler most developers had available. Now they have two (although clang does try to support almost everything GCC does, so it doesn't say a huge amount about portability). 4. If you want to quickly see whether an optimization was applied (like inlining or loop unrolling), looking at LLVM is more approachable, so clang is nice for that.
- illivah 11y ago
  why would the GPL matter for using gcc? It's not like you're modifying, distributing, and selling forks of gcc, it's just a compiler.
  - sqeaky 11y ago
    You are using logic, not all decision makers do. Some hear "GPL" and react, "oh that's the viral license can't use anything with that".
    - jeffdavis 11y ago
      See sibling comment.
  - jeffdavis 11y ago
    Runtime code generation / JIT.
ajdecon 11y ago
gcc also supports OpenMP 4.x and OpenACC, both of which are used extensively in the HPC world to support automated parallelization and offloading to accelerators like GPUs. clang only recently added support for OpenMP 3.1, and my understanding is that there are no plans for OpenACC support.
Keyframe 11y ago
Out of inertia, I use gcc on all three platforms and it has been good towards me. Sometimes I need to compile a specific library on OSX with clang, but it works just fine with gcc ones as well (using ar provided with XCode CLI Tools). Mind you that I use C, not C++ and I tend to grab a GCC snapshot now and then and compile it and use it like that.
Camillo 11y ago
> Edit 2: Intel also makes compilers, to which I own, but never use. I see this more and more often on Reddit, from posters I assume are millennials, and I am interested in the psychology of this error. Why do you put a "to" before "which"? You would not say "I own to an Intel compiler". I never see people make this mistake with other pronouns, either: for instance, they will correct turn "I saw pg yesterday" into "pg, whom I saw yesterday". What is it about "which" specifically that makes it hard for kids to use?
- loeg 11y ago
  This person made at least four other grammar errors. I don't think they are a native English speaker.
  - Camillo 11y ago
    Neither am I. I would be curious to know if this particular error is associated with a particular mother tongue.
    - loeg 11y ago
      If their Github is anything to go by, they appear to work for a Chinese company.
J_Darnley 11y ago
Well I see your edit mentions Windows and that was the problem when I last tried clang. It failed to compile FFmpeg. I don't know whether that is because it doesn't work, or didn't work, or my package was just outdated. GCC works. And once you force gcc to have colored messages there seems to be little advantage to using clang over it.

jcranmer 11y ago

gcc generally provides somewhat better code than clang, both in runtime and in object size. Clang has traditionally done better at warnings and diagnostics, although gcc has definitely closed that space in the past few years (since 4.9 or so).

jason_slack 11y ago
are there circumstances where a developer should compile their products with more than one compiler to flush out issues, potentially fine tune/optimize code, etc? I've never thought about doing this.
- lallysingh 11y ago
  Yes, at least make sure that your code compiles and the tests pass on more than one. That way you're sure that you're not depending on peculiars of one compiler (their specific behaviors that are undefined in the standard, optimizer actions, etc).
  - bschwindHN 11y ago
    And a nice way to run multiple compilers easily is by using a tool like Travis CI with their compiler matrix support. https://docs.travis-ci.com/user/languages/c https://docs.travis-ci.com/user/languages/c
- corysama 11y ago
  When I was working on multi-platform console engines, I had no choice but to compile with several highly varying compilers. It teaches you very quickly how quietly compiler-specific extensions and quirks work their way into your code. Also, different dev environments offer different tools. A nice benefit of running in lots of environments was that I often could pick between the best tools of any platform whenever I had a problem they could help solve.
- gaius 11y ago
  At a previous job we ensured we got clean compiles with Visual C++, SPARCworks and xlc, even tho' all our customers were only actually interested in the Solaris version.
- EliRivers 11y ago
  Yes; whenever they want to produce a higher quality product. Which I'd anticipate being "whenever possible", limited only by compiler extensions one has to use, and dev/target hardware.
- danieltillett 11y ago
  From experience make sure you compile 32bit and 64bit versions too - this flushed out a surpring number of bugs.
- blue11 11y ago
  I've worked at places where we maintained a dual build, VisualC++ and Linux gcc, because we wanted to be able to develop and run in multiple environments. That forces you to write clean standard-compliant code, although in some cases it could be a pain.

gravypod 11y ago

GCC, from my experience, generates much faster binaries. Clang is much faster at compiling though. It's a trade off.

octoploid 11y ago
Correction. Clang used to compile much faster years ago. But nowadays GCC-6 actually compiles faster than clang-3.8.0. See e.g.: http://hubicka.blogspot.com/2016/03/building-libreoffice-with-gcc-6-and-lto.html http://hubicka.blogspot.com/2016/03/building-libreoffice-wit...
PeCaN 11y ago
That was the case circa 2012 with Clang 3.1 and GCC 4.7, but both have closed the gaps. Clang generates code roughly as fast as GCC and GCC compiles about as fast as Clang.
- agumonkey 11y ago
  funny how this opposite spectrum leads to https://upload.wikimedia.org/wikipedia/commons/7/7c/Vector_Addition.png https://upload.wikimedia.org/wikipedia/commons/7/7c/Vector_A... risc / cisc gathered around each other, clang / gcc... progress by antagonism

jordigh 11y ago

Different set of bugs (I know of more annoying bugs in clang and libc++ than I do of their GNU counterparts, perhaps only because I know gcc better), different performance in the generated code. Try them both and benchmark, see which you like best. I believe you can get gcc from homebrew, but beware of linking gcc-built code with libstdc++ and not libc++. http://stackoverflow.com/questions/18976922/how-to-use-the-gcc-compiler-in-the-mac-terminal-instead-of-clang http://stackoverflow.com/questions/18976922/how-to-use-the-g...

pjmlp 11y ago

There are quite a few other compilers available, if you look into commercial UNIXes, embedded and real time OSes, game consoles, HPC.

kkylin 11y ago

It also depends a little bit on your style of programming. For example, in C code, I personally like using gcc extensions like nested functions. As far as I know this is not supported by clang (but perhaps someone more knowledgeble can chime in).

Kristine1975 11y ago
>nested functions They are not supported. In C++11 you can use lambdas: auto const local_func = [&](...) { ... }; And then later: local_func(...);
- CyberDildonics 11y ago
  Not only that but you can even create a struct inside a function and overload operator(). I don't know if this is possible in C++03 or not.
  - Kristine1975 11y ago
    >I don't know if this is possible in C++03 or not. It is/was. It could be used to manually create a lambda function.
    - lultimouomo 11y ago
      But note that you cannot use such class as a template parameter, as it has no linkage. Which makes it mostly useless, since you usually want to use lambdas with templates. This restriction has been lifted in C++11.
    - CyberDildonics 11y ago
      Inside of a function too?
- kkylin 11y ago
  Cool, thanks!

brandmeyer 11y ago

Right now, clang is missing several features that I care about, but most of the industry doesn't[1]. Clang is a 90% or maybe 95% solution, and my use cases aren't covered. So I don't use it. That said, I am grateful for the competition: GCC has definitely been getting better thanks to clang. [1] Namely, -Wdouble-promotion, big-endian ARM interrupt handlers, -fstack-usage, -Og, -fno-delete-null-pointer-checks, -falign-functions

beeforpork 11y ago
+1 for -fno-delete-null-pointer-checks But actually, what I'd rather like is -fno-optimise-based-on-undefined-behaviour.
- brandmeyer 11y ago
  -fno-delete-null-pointer-checks In my particular case, I'm programming in a microcontroller environment where there is ordinary RAM at the NULL address. Dereferencing NULL therefore doesn't halt the program at all.
  - teddyh 11y ago
    Your compiler, or rather your architecture definition supplied to the compiler, is broken. NULL should be an invalid pointer value — it need not actually be memory address 0. (The explicit constant 0 in a pointer context should be automatically translated by the compiler into this special invalid pointer value.) There have been several such architectures already, so this should not present an insurmountable problem.
  - yrro 11y ago
    AIUI, this code is not affected: X *foo = ...; if (foo) foo->bar(); But this code will be: X *foo = ...; foo->bar(); if (foo) { ... } Since foo is dereferenced unconditionally, the compiler is allowed to assume that it will not be null in the above code, and therefore the test on the third line to determine whether foo is null or not is useless and can be omitted.

Esau 11y ago

The one thing I hear mentioned is that GCC supports more processors than Clang does. I believe this is the reason that NetBSD and OpenBSD still use GCC.

maaku 11y ago
What do you mean by support more processors?
- jlg23 11y ago
  The comment was referring to CPU architectures.
  - maaku 11y ago
    I understand that. Still, what was meant? C/C++ don't have mechanisms for automatic parallelization, or if there are obscure extensions they are not commonly used. Compilation is usually a single-processor task, with linear speedup obtained by doing multiple compilation units in parallel (make -jN). So in what way can a compiler be "better" for multi-processor / multi-core CPU architectures?
    - MereInterest 11y ago
      I believe that in this context, "more processors" meant "more different models of processors". That is, there exist processors for which gcc can produce binaries and clang cannot produce binaries.
      - maaku 11y ago
        Ah ok. More backends.
        groovy2shoes 11y ago
        Well, support for more target architectures, really. I can easily imagine cases where a compiler could have multiple backends for the same target arch, so the number of backends could be misleading in that regard. For a summary from the OpenBSD perspective, see here: http://marc.info/?l=openbsd-misc&m=137530560232232&w=2 http://marc.info/?l=openbsd-misc&m=137530560232232&w=2

Kristine1975 11y ago

IIRC gcc generates somewhat faster machine code. clang is available for Windows as clang-cl from here: http://llvm.org/releases/download.html http://llvm.org/releases/download.html Here's the status page for compatibility with MSVC (clang 3.9, i.e. current development version): http://clang.llvm.org/docs/MSVCCompatibility.html http://clang.llvm.org/docs/MSVCCompatibility.html

jeffdavis 11y ago

1. License. If you are worried about GPL (especially v3), then you are better off with clang. 2. GCC is generally considered to produce better binaries. 3. Smart projects will support both and test with both. Before, even though projects tried to be portable, GCC was the only compiler most developers had available. Now they have two (although clang does try to support almost everything GCC does, so it doesn't say a huge amount about portability). 4. If you want to quickly see whether an optimization was applied (like inlining or loop unrolling), looking at LLVM is more approachable, so clang is nice for that.

illivah 11y ago
why would the GPL matter for using gcc? It's not like you're modifying, distributing, and selling forks of gcc, it's just a compiler.
- sqeaky 11y ago
  You are using logic, not all decision makers do. Some hear "GPL" and react, "oh that's the viral license can't use anything with that".
  - jeffdavis 11y ago
    See sibling comment.
- jeffdavis 11y ago
  Runtime code generation / JIT.

ajdecon 11y ago

gcc also supports OpenMP 4.x and OpenACC, both of which are used extensively in the HPC world to support automated parallelization and offloading to accelerators like GPUs. clang only recently added support for OpenMP 3.1, and my understanding is that there are no plans for OpenACC support.

Keyframe 11y ago

Out of inertia, I use gcc on all three platforms and it has been good towards me. Sometimes I need to compile a specific library on OSX with clang, but it works just fine with gcc ones as well (using ar provided with XCode CLI Tools). Mind you that I use C, not C++ and I tend to grab a GCC snapshot now and then and compile it and use it like that.

Camillo 11y ago

> Edit 2: Intel also makes compilers, to which I own, but never use. I see this more and more often on Reddit, from posters I assume are millennials, and I am interested in the psychology of this error. Why do you put a "to" before "which"? You would not say "I own to an Intel compiler". I never see people make this mistake with other pronouns, either: for instance, they will correct turn "I saw pg yesterday" into "pg, whom I saw yesterday". What is it about "which" specifically that makes it hard for kids to use?

loeg 11y ago
This person made at least four other grammar errors. I don't think they are a native English speaker.
- Camillo 11y ago
  Neither am I. I would be curious to know if this particular error is associated with a particular mother tongue.
  - loeg 11y ago
    If their Github is anything to go by, they appear to work for a Chinese company.

J_Darnley 11y ago

Well I see your edit mentions Windows and that was the problem when I last tried clang. It failed to compile FFmpeg. I don't know whether that is because it doesn't work, or didn't work, or my package was just outdated. GCC works. And once you force gcc to have colored messages there seems to be little advantage to using clang over it.