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Honest question: what value does GCC have in 2020? It seems like llvm is the better designed compiler, more commercial support, more permissive license, etc. Pr

by smabie 7y ago

Honest question: what value does GCC have in 2020? It seems like llvm is the better designed compiler, more commercial support, more permissive license, etc. Pretty much everyone designing new languages today is using LLVM for backend codegen; and the people who aren't sure as hell are not using GCC.

umvi 7y ago
How's LLVM's code coverage performance? Starting with GCC 9, you can stream gcov straight to stdout in json format, which allowed me to write a multi-core coverage aggregation/analysis tool[1] to replace lcov (and is over 100x faster than lcov, in my case - ymmv): [1] https://github.com/RPGillespie6/fastcov https://github.com/RPGillespie6/fastcov
- touisteur 7y ago
  Aaaah if only I could do this to a runtime defined fd or pipe... Live coverage information! Have to use Intel PT for this but sometimes feels like a big hammer :-)
alfalfasprout 7y ago
It's still the "de facto" compiler on most flavors of Linux and still tends to produce faster binaries in practice than Clang. That gap, however, continues to narrow.
- CannoloBlahnik 7y ago
  I always viewed Clang as faster, and perceived GCC as catching up.
  - throwaway744678 7y ago
    Clang has faster compilation, but (depending on the actual case) optimized binary built by gcc run faster; as mentioned above, both gaps are narrowing.
  - MaxBarraclough 7y ago
    As of May 2019, Phoronix showed them being roughly equal, with the winner depending on the application. https://www.phoronix.com/scan.php?page=article&item=gcc9-clang8-hedt&num=3 https://www.phoronix.com/scan.php?page=article&item=gcc9-cla... We should expect them to both continue to improve. It's not a sure thing that Clang will end up the clear winner.
  - eMSF 7y ago
    The perception of Apple's Midas Touch has never been dependent on banal things like objective comparisons.
- mratsim 7y ago
  GCC is bad for anything related to big integer arithmetic or cryptography unfortunately. Something like 20 to 40% slower than Clang. Example of GCC awful codegen on add with carry: https://gcc.godbolt.org/z/2h768y https://gcc.godbolt.org/z/2h768y
gmfawcett 7y ago
GCC has the same value that LLVM had when it was first released: healthy competition for the market leader. The need to compete with LLVM was the best thing that ever happened to the GCC project. A world with only LLVM could easily lead back to a stagnant monoculture. Therefore, it's in everyone's selfish interest to promote and use both toolchains.
- BiteCode_dev 7y ago
  See also: - firefox and chrome - ios and android - mysql and postgres
  - MaxBarraclough 7y ago
    - AMD and Intel - C# and Java More generally of course, healthy competition is good. There are more than 2 serious Java IDEs, for instance.
asveikau 7y ago
Right now, or last I checked, GCC supports more architectures. So while I realize that the Intel/ARM monoculture (or duoculture?) plus occasional emergence of things like risc-v will continue to absorb the world's new devices, there will probably be niche uses of GCC to target obscure hardware for a long time.
homarp 7y ago
Competition and less permissive license (the license kind of ensures gcc can not be 'closed' and therefore ensure that llvm's license stays 'more permissive').
geofft 7y ago
A few things off the top of my head, influenced by both trying to build Rust code for the Linux kernel as a hobby and maintaining compilers in my day job: - GCC still supports more architectures/platforms than LLVM does. Apart from various rare/obscure/embedded platforms, one notable one (I think) is x86-16: .code16gcc pretty much works, LLVM only kinda supports it. - GCC has its own plugin interface. If you already have GCC plugins, you probably want to stick with GCC. - If you have a large legacy codebase that's probably got some UB somewhere because that's the nature of having large codebases written by fallible humans, it's probably less likely that a new versions of the same compiler will misinterpret your intentions than a new compiler would. (But this is a weak argument, since new versions could still change their interpretation/behavior.)
chrisseaton 7y ago
I think GCC often still outperforms LLVM for many people's workloads. Not sure why that is - haven't we gotten to the point where any missing optimisations can just be added to LLVM? Are some optimisations very hard to add given LLVM's architecture? There must be enough people and companies working on it by now to fix anything? But if you're really serious about performance presumably you're using Intel.
- dahart 7y ago
  > But if you're really serious about performance presumably you're using Intel. Or a GPU?
  - chrisseaton 7y ago
    We (as an industry) just don't know how to put some programs onto the GPU yet.
    - dahart 7y ago
      Agreed, true!
  - BubRoss 7y ago
    Or an FPGA or an ASIC, but this is obviously.in the context of CPUs.
bluecalm 7y ago
I use it because it outperforms both Intel and Clang on my code by significant margin. Open MP support in Clang on Windows comes and goes and no one cares (I don't blame them, it's a niche use case but still). I don't see any reason to switch tbh. GCC does the job, is around for much longer, supports more stuff and generates more efficient code (at least in my case).
craigsmansion 7y ago
At the very least GCC is keeping llvm permissively licensed. llvm is partly a product of Apple's dislike of copyleft licenses. Without gcc there is no reason for llvm's large proprietary contributors to stick to the "more permissive license" and simply close it down and distribute it as "value added" binaries.
yjftsjthsd-h 7y ago
I'm having trouble finding whether this is still true, but for a long time gcc was the only supported option for building Linux (the kernel). I know there's been work to make it build with clang, but it at least used to be that you needed some patches.
- Someone 7y ago
  That isn’t true anymore, not even for x86_64 (https://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNotes.html#linux-kernel https://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNote...)
  - yjftsjthsd-h 7y ago
    Oh, excellent:) Thanks for sharing an official source for that.
pengaru 7y ago
> more permissive license Not everyone favors a more permissive license.
- rnd0 7y ago
  There's permissive and then there's exploitable. People who benefit (financially) from being able use other people's work without contributing their own changes would prefer us to call it "permissive" instead of "exploitive". It's sad that the movement which originally democratized computing (by placing development tools into the hands of ordinary users) is slowly being changed into a pyramid scheme that fleeces volunteers. So, to echo other comments in this thread; GCC keeps the corporate BSD crowd honest, and postpones the day when they lock up their code.
nwallin 7y ago
It produces faster binaries than clang, sometimes significantly so. ICC produces faster binaries than GCC, but ICC is expensive and GCC is free. MSVC is garbage.
- pjmlp 7y ago
  Desktop and Game developers happen to share a different opinion.
  - MaxBarraclough 7y ago
    Does ICC have any traction in the gaming world?
    - pjmlp 7y ago
      It does on Windows shops that care about the ultimate performance optimization on Intel CPUs and vtune integration.
      - MaxBarraclough 7y ago
        Doesn't that describe all high-budget games? Would the average Unreal-based game be built with ICC?
        pjmlp 7y ago
        Depends on the studio. Here is an overview and some testimonials, https://software.intel.com/en-us/gamedev/tools https://software.intel.com/en-us/gamedev/tools
        MaxBarraclough 7y ago
        At a glance it seems the answer is No. Unreal Engine 4 doesn't officially support icc, for instance. Neither does the Source Engine. I believe the same goes for CryEngine.
brandmeyer 7y ago
Here's a key paragraph from Anandtech's recent article on ARM in AWS: > Overall, I checked three different compiler setups: A freshly compiled GCC 9.2.0 release, Arm’s Allinea Studio Compiler 20 package which comes with both Arm’s closed source LLVM and Flang variants as well as a pre-compiled version of GCC 9.2.0, and Marvell’s branch of LLVM and Flang. Note the phrases "ARM's closed source LLVM" and "Marvell's branch of LLVM". That's why GCC is still critical. Because LLVM is already suffering from the fragmentation and proprietary forks that BSD has always suffered from.

by smabie 7y ago

umvi 7y ago

How's LLVM's code coverage performance? Starting with GCC 9, you can stream gcov straight to stdout in json format, which allowed me to write a multi-core coverage aggregation/analysis tool[1] to replace lcov (and is over 100x faster than lcov, in my case - ymmv): [1] https://github.com/RPGillespie6/fastcov https://github.com/RPGillespie6/fastcov

touisteur 7y ago
Aaaah if only I could do this to a runtime defined fd or pipe... Live coverage information! Have to use Intel PT for this but sometimes feels like a big hammer :-)

alfalfasprout 7y ago

It's still the "de facto" compiler on most flavors of Linux and still tends to produce faster binaries in practice than Clang. That gap, however, continues to narrow.

CannoloBlahnik 7y ago
I always viewed Clang as faster, and perceived GCC as catching up.
- throwaway744678 7y ago
  Clang has faster compilation, but (depending on the actual case) optimized binary built by gcc run faster; as mentioned above, both gaps are narrowing.
- MaxBarraclough 7y ago
  As of May 2019, Phoronix showed them being roughly equal, with the winner depending on the application. https://www.phoronix.com/scan.php?page=article&item=gcc9-clang8-hedt&num=3 https://www.phoronix.com/scan.php?page=article&item=gcc9-cla... We should expect them to both continue to improve. It's not a sure thing that Clang will end up the clear winner.
- eMSF 7y ago
  The perception of Apple's Midas Touch has never been dependent on banal things like objective comparisons.
mratsim 7y ago
GCC is bad for anything related to big integer arithmetic or cryptography unfortunately. Something like 20 to 40% slower than Clang. Example of GCC awful codegen on add with carry: https://gcc.godbolt.org/z/2h768y https://gcc.godbolt.org/z/2h768y

gmfawcett 7y ago

GCC has the same value that LLVM had when it was first released: healthy competition for the market leader. The need to compete with LLVM was the best thing that ever happened to the GCC project. A world with only LLVM could easily lead back to a stagnant monoculture. Therefore, it's in everyone's selfish interest to promote and use both toolchains.

BiteCode_dev 7y ago
See also: - firefox and chrome - ios and android - mysql and postgres
- MaxBarraclough 7y ago
  - AMD and Intel - C# and Java More generally of course, healthy competition is good. There are more than 2 serious Java IDEs, for instance.

asveikau 7y ago

Right now, or last I checked, GCC supports more architectures. So while I realize that the Intel/ARM monoculture (or duoculture?) plus occasional emergence of things like risc-v will continue to absorb the world's new devices, there will probably be niche uses of GCC to target obscure hardware for a long time.

homarp 7y ago

Competition and less permissive license (the license kind of ensures gcc can not be 'closed' and therefore ensure that llvm's license stays 'more permissive').

geofft 7y ago

A few things off the top of my head, influenced by both trying to build Rust code for the Linux kernel as a hobby and maintaining compilers in my day job: - GCC still supports more architectures/platforms than LLVM does. Apart from various rare/obscure/embedded platforms, one notable one (I think) is x86-16: .code16gcc pretty much works, LLVM only kinda supports it. - GCC has its own plugin interface. If you already have GCC plugins, you probably want to stick with GCC. - If you have a large legacy codebase that's probably got some UB somewhere because that's the nature of having large codebases written by fallible humans, it's probably less likely that a new versions of the same compiler will misinterpret your intentions than a new compiler would. (But this is a weak argument, since new versions could still change their interpretation/behavior.)

chrisseaton 7y ago

I think GCC often still outperforms LLVM for many people's workloads. Not sure why that is - haven't we gotten to the point where any missing optimisations can just be added to LLVM? Are some optimisations very hard to add given LLVM's architecture? There must be enough people and companies working on it by now to fix anything? But if you're really serious about performance presumably you're using Intel.

dahart 7y ago
> But if you're really serious about performance presumably you're using Intel. Or a GPU?
- chrisseaton 7y ago
  We (as an industry) just don't know how to put some programs onto the GPU yet.
  - dahart 7y ago
    Agreed, true!
- BubRoss 7y ago
  Or an FPGA or an ASIC, but this is obviously.in the context of CPUs.

bluecalm 7y ago

I use it because it outperforms both Intel and Clang on my code by significant margin. Open MP support in Clang on Windows comes and goes and no one cares (I don't blame them, it's a niche use case but still). I don't see any reason to switch tbh. GCC does the job, is around for much longer, supports more stuff and generates more efficient code (at least in my case).

craigsmansion 7y ago

At the very least GCC is keeping llvm permissively licensed. llvm is partly a product of Apple's dislike of copyleft licenses. Without gcc there is no reason for llvm's large proprietary contributors to stick to the "more permissive license" and simply close it down and distribute it as "value added" binaries.

yjftsjthsd-h 7y ago

I'm having trouble finding whether this is still true, but for a long time gcc was the only supported option for building Linux (the kernel). I know there's been work to make it build with clang, but it at least used to be that you needed some patches.

Someone 7y ago
That isn’t true anymore, not even for x86_64 (https://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNotes.html#linux-kernel https://releases.llvm.org/9.0.0/tools/clang/docs/ReleaseNote...)
- yjftsjthsd-h 7y ago
  Oh, excellent:) Thanks for sharing an official source for that.

pengaru 7y ago

> more permissive license Not everyone favors a more permissive license.

rnd0 7y ago
There's permissive and then there's exploitable. People who benefit (financially) from being able use other people's work without contributing their own changes would prefer us to call it "permissive" instead of "exploitive". It's sad that the movement which originally democratized computing (by placing development tools into the hands of ordinary users) is slowly being changed into a pyramid scheme that fleeces volunteers. So, to echo other comments in this thread; GCC keeps the corporate BSD crowd honest, and postpones the day when they lock up their code.

nwallin 7y ago

It produces faster binaries than clang, sometimes significantly so. ICC produces faster binaries than GCC, but ICC is expensive and GCC is free. MSVC is garbage.

pjmlp 7y ago
Desktop and Game developers happen to share a different opinion.
- MaxBarraclough 7y ago
  Does ICC have any traction in the gaming world?
  - pjmlp 7y ago
    It does on Windows shops that care about the ultimate performance optimization on Intel CPUs and vtune integration.
    - MaxBarraclough 7y ago
      Doesn't that describe all high-budget games? Would the average Unreal-based game be built with ICC?
      - pjmlp 7y ago
        Depends on the studio. Here is an overview and some testimonials, https://software.intel.com/en-us/gamedev/tools https://software.intel.com/en-us/gamedev/tools
        MaxBarraclough 7y ago
        At a glance it seems the answer is No. Unreal Engine 4 doesn't officially support icc, for instance. Neither does the Source Engine. I believe the same goes for CryEngine.

brandmeyer 7y ago

Here's a key paragraph from Anandtech's recent article on ARM in AWS: > Overall, I checked three different compiler setups: A freshly compiled GCC 9.2.0 release, Arm’s Allinea Studio Compiler 20 package which comes with both Arm’s closed source LLVM and Flang variants as well as a pre-compiled version of GCC 9.2.0, and Marvell’s branch of LLVM and Flang. Note the phrases "ARM's closed source LLVM" and "Marvell's branch of LLVM". That's why GCC is still critical. Because LLVM is already suffering from the fragmentation and proprietary forks that BSD has always suffered from.