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I am considering the question of transpiling a language (home-grown DSL) to C vs to C++.
I haven't done any 'native' programming for over 15 years, so I want to check my assumptions.
Am I right into assuming that transpiling to the newest C++ version (17) would enable the native compiler to use a much wider range of 'modern' Intel/AMD CPU instructions, resulting in a more efficient executable (beyond the multi-threading / memory-model part of C++, which already by itself seems a good enough reason to go for C++)?
Put another way, isn't a large part of 'more recent' CPU instructions never generated by a C compiler, simply because it has too little information about the programmer intent, due to the simpler syntax of C? I know I could access all CPU instructions with assembler, but that is precisely what I don't want to do. Ideally, I would want the generated code to still be as platform-independent as possible.
All of your assumptions about the relationship between programming language and "modern CPU instructions" are incorrect.
Let's consider the GNU Compiler Collection.
The choice of language here doesn't much matter, as the language front-ends all end up generating the same intermediate form called GIMPLE. The optimizing passes then work on that.
The range of CPU instructions which can be emitted is controlled by the -mtune option. For x86, GCC is capable of emitting modern AVX 512 instructions when optimizing some very plain-looking C code. Automatic loop vectorisation is a powerful thing. Try it out: implement memcpy and look at the generated assembly.
My advice: generate clean, un-clever C code, and crank up the optimization level. Just like you would do if writing code by hand.
You might also consider implementing your language directly as a front-end to GCC or LLVM, without transpiling to C or C++. LLVM was designed for this purpose, intended to make implementing new languages easy, and still taking advantage of modern optimization approaches.
For a language like C++ the existence of a standard is a must. And good compilers try their best (well, most of the good compilers, at least) to comply. Many compilers have language extensions, some of which are allowed by the standard, some of which are not. Of the latter kind 2 examples:
gcc's typeof
microsoft's compilers allow a pure virtual function declaration to have both a pure-specifier(=0) and a definition (which is prohibited by the standard - let's not discuss why, that's another topic:)
(there are many other examples)
Both examples are useful in the following sense: example1 is a very useful feature which will be available in c++0x under a different name. example2 is also useful, and microsoft has decided not to respect the ban that made no sense.
And I am grateful that compilers provide language extensions that help us developers in our routine. But here's a question: shouldn't there be an option which, when set, mandates that the compiler be as standards compliant as it can, no matter whether they agree with the standard or not. For example visual studio has such an option, which is called disable language extensions. But hey, they still allow example2.
I want everyone to understand my question correctly. It is a GREAT thing that MSVC allows example2, and I would very much like that feature to be in the standard. It doesn't break any compliant code, it does nothing bad. It just isn't standard.
Would you like that microsoft disable example2 when disable language extensions is set to true? Note that the words microsoft, example2, etc. are placeholders :)
Why?
Again, just to make sure. The crucial point is: Should a compiler bother to provide a compliant version (optionally set in the settings)(in its limits, e.g. I am not talking about export) for a certain feature when they provide a better alternative that is not standard and is perhaps even a superset of the standard, thus not breaking anything.
Standards compliance is important for the fundamental reason that it makes your code easier to maintain. This manifests in a number of ways:
Porting from one version of a compiler to another. I once had to post a 1.2 million-LOC app from VC6 to VC9. VC6 was notorious for being horribly non-Compliant, even when it was new. It allowed non-compliant code even on the highest warning levels that the new compiler rejected at the lowest. If the code had been written in a more compliant way in the first place, this project wouldn't (shouldn't)have taken 3 months.
Porting from one platform to another. As you say, the current MS compilers have language extensions. Some of these are shared by compilers on other platforms, some are not. Even if they are shared, the behavior may be subtly different. Writing compliant code, rather that using these extensions, makes your code correct from the word go. "Porting" becomes simply pulling the tree down and doing a rebuild, rather than digging through the bowels of your app trying to figure out why 3 bits are wrong.
C++ is defined by the standard. The extensions used by compilers changes the language. New programmers coming online who know C++ but not the dialect your compiler uses will get up to speed more quickly if you write to Standard C++, rather than the dialect that your compiler supports.
First, a reply to several comments. The MS VC extension in question is like this:
struct extension {
virtual void func() = 0 { /* function body here */ }
};
The standard allows you to implement the pure virtual function, but not "in place" like this, so you have to write it something like this instead:
struct standard {
virtual void func() = 0;
};
void standard::func() { ; }
As to the original question, yes, I think it's a good idea for the compiler to have a mode in which it follows (and enforces) the standard as accurately as possible. While most compilers have that, the result isn't necessarily as accurate a representation of the standard as you/I would like.
At least IMO, about the only answer to this is for people who care about portability to have (and use) at least a couple of compilers on a regular basis. For C++, one of those should be based on the EDG front-end; I believe it has substantially better conformance than most of the others. If you're using Intel's compiler on a regular basis anyway, that's fine. Otherwise, I'd recommend getting a copy of Comeau C++; it's only $50, and it's the closest thing to a "reference" available. You can also use Comeau online, but if you use it on a regular basis, it's worth getting a copy of your own.
Not to sound like an EDG or Comeau shill or anything, but even if you don't care much about portability, I'd recommend getting a copy anyway -- it generally produces excellent error messages. Its clean, clear error messages (all by themselves) have saved enough time over the years to pay for the compiler several times over.
Edit: Looking at this again, some of the advice is looking pretty dated, especially the recommendation for EDG/Comeau. In the three years since I originally wrote this, Clang has progressed from purely experimental to being quite reasonable for production use. Likewise, the gcc maintainers have (IMO) made great strides in conformance as well.
During the same time, Comeau hasn't released a single new version of their compiler, and there's been a new release of the C++ standard. As a result, Comeau is now fairly out of date with respect to the current standard (and the situation seems to be getting worse, not better -- the committee has already approved a committee draft of a new standard that is likely to become C++14).
As such, although I recommended Comeau at that time, I'd have difficulty (at best) doing so today. Fortunately, most of the advantages it provided are now available in more mainstream compilers -- both Clang and gcc have improved compliance (substantially) as outlined above, and their error messages have improved considerably as well (Clang has placed a strong emphasis on better error messages, almost from its inception).
Bottom line: I'd still recommend having at least two compilers installed and available, but today I'd probably choose different compilers than I did when I originally wrote this answer.
"Not breaking anything" is such a slippery slope in the long run, that it's better to avoid it altogether. My company's main product outlived several generations of compilers (first written in 1991, with RW), and combing through compiler extensions and quiet standards violations whenever it was the time to migrate to a newer dev system took a lot of effort.
But as long as there's an option to turn off or at least warn about 'non-standard extension', I'm good with it.
34, 70, 6.
I would certainly want an option that disables language extensions to disable all language extensions. Why?
All options should do what they say they do.
Some people need to develop portable code, requiring a compiler that only accepts the standard form of the language.
"Better" is a subjective word. Language extensions are useful for some developers, but make things more difficult for others.
I think that it's critical that a compiler provide a standards-only mode if it wants to be the primary one used while developing. All compilers should, of course, compile standards compliant code, but it's not critical they they don't extend if they don't think of themselves as the primary compiler -- for example, a cross-compiler, or a compiler for a less popular platform that is nearly always ported to, rather than targeted.
Extensions are fine for any compiler, but it would be nice if I had to turn them on if I want them. By default, I'd prefer a standards-only compiler.
So, given that, I expect MSVC to be standards-only by default. The same with gcc++.
Stats: 40, 90, 15
I think standards compliance is very important.
I always consider source code is more for the human readers than for the machine(s). So, to communicate programmer's intention to the reader, abiding the standard is like speaking a language of lowest common denominator.
Both at home and work, I use g++, and I have aliased it with the following flags for strict standard compliance.
-Wall -Wextra -ansi -pedantic -std=c++98
Check out this page on Strict ANSI/ISO
I am not a standards expert, but this has served me well. I have written STL-style container libraries which run as-is on different platforms, e.g. 32-bit linux, 64-bit linux, 32-bit solaris, and 32-bit embedded OSE.
Consider indicators on cars (known as "turn signals" in some jurisdictions); they are a reliable way to determine which direction someone's going to turn off a roundabout... until just one person doesn't use them at all. Then the whole system breaks down.
It didn't "hurt anyone" or obviously "break anything" in IE when they allowed document.someId to be used as a shortcut for document.getElementById('someId').... however, it did spawn an entire generation of coders and even books that consequently thought it was okay and right, because "it works". Then, suddenly, the ten million resulting websites were entirely non-portable.
Standards are important for interoperability, and if you don't follow them then there's little point in having them at all.
Standards-compliance hounds may get hated for "pedanticism" but, really, until everybody follows suit you're going to have portability and compatibility problems for ever.
How important standards-compliance is depends on what you are trying to achieve.
If you are writing a program that will never be ported outside of its current environment (especially a program that you're not planning to develop/support for a long time) then it's not very important. Whatever works, works.
If you need your program to remain relevant for a long time, and be easily portable to different environments, than you will want it to be standards compliant, since that's the only way to (more or less) guarantee that it will work everywhere.
The trick, of course, is figuring out which situation you are actually in. It's very common to start a program thinking it is a short-term hack, and later on find that it's so useful that you're still developing/maintaining it years later. In that situation your life will be much less unpleasant if you didn't make any short-sighted design decisions at the beginning of the program's lifetime.
Is anyone here using the Intel C++ compiler instead of Microsoft's Visual c++ compiler?
I would be very interested to hear your experience about integration, performance and build times.
The Intel compiler is one of the most advanced C++ compiler available, it has a number of advantages over for instance the Microsoft Visual C++ compiler, and one major drawback. The advantages include:
Very good SIMD support, as far as I've been able to find out, it is the compiler that has the best support for SIMD instructions.
Supports both automatic parallelization (multi core optimzations), as well as manual (through OpenMP), and does both very well.
Support CPU dispatching, this is really important, since it allows the compiler to target the processor for optimized instructions when the program runs. As far as I can tell this is the only C++ compiler available that does this, unless G++ has introduced this in their yet.
It is often shipped with optimized libraries, such as math and image libraries.
However it has one major drawback, the dispatcher as mentioned above, only works on Intel CPU's, this means that advanced optimizations will be left out on AMD cpu's. There is a workaround for this, but it is still a major problem with the compiler.
To work around the dispatcher problem, it is possible to replace the dispatcher code produced with a version working on AMD processors, one can for instance use Agner Fog's asmlib library which replaces the compiler generated dispatcher function. Much more information about the dispatching problem, and more detailed technical explanations of some of the topics can be found in the Optimizing software in C++ paper - also from Anger (which is really worth reading).
On a personal note I have used the Intel c++ Compiler with Visual Studio 2005 where it worked flawlessly, I didn't experience any problems with microsoft specific language extensions, it seemed to understand those I used, but perhaps the ones mentioned by John Knoeller were different from the ones I had in my projects.
While I like the Intel compiler, I'm currently working with the microsoft C++ compiler, simply because of the financial extra investment the Intel compiler requires. I would only use the Intel compiler as an alternative to Microsofts or the GNU compiler, if performance were critical to my project and I had a the financial part in order ;)
I'm not using Intel C++ compiler at work / personal (I wish I would).
I would use it because it has:
Excellent inline assembler support. Intel C++ supports both Intel and AT&T (GCC) assembler syntaxes, for x86 and x64 platforms. Visual C++ can handle only Intel assembly syntax and only for x86.
Support for SSE3, SSSE3, and SSE4 instruction sets. Visual C++ has support for SSE and SSE2.
Is based on EDG C++, which has a complete ISO/IEC 14882:2003 standard implementation. That means you can use / learn every C++ feature.
I've had only one experience with this compiler, compiling STLPort. It took MSVC around 5 minutes to compile it and ICC was compiling for more than an hour. It seems that their template compilation is very slow. Other than this I've heard only good things about it.
Here's something interesting:
Intel's compiler can produce different
versions of pieces of code, with each
version being optimised for a specific
processor and/or instruction set
(SSE2, SSE3, etc.). The system detects
which CPU it's running on and chooses
the optimal code path accordingly; the
CPU dispatcher, as it's called.
"However, the Intel CPU dispatcher
does not only check which instruction
set is supported by the CPU, it also
checks the vendor ID string," Fog
details, "If the vendor string says
'GenuineIntel' then it uses the
optimal code path. If the CPU is not
from Intel then, in most cases, it
will run the slowest possible version
of the code, even if the CPU is fully
compatible with a better version."
OSnews article here
I tried using Intel C++ at my previous job. IIRC, it did indeed generate more efficient code at the expense of compilation time. We didn't put it to production use though, for reasons I can't remember.
One important difference compared to MSVC is that the Intel compiler supports C99.
Anecdotally, I've found that the Intel compiler crashes more frequently than Visual C++. Its diagnostics are a bit more thorough and clearly written than VC's. Thus, it's possible that the compiler will give diagnostics that weren't given with VC, or will crash where VC didn't, making your conversion more expensive.
However, I do believe that Intel's compiler allows you to link with Microsoft runtimes like the CRT, easing the transition cost.
If you are interoperating with managed code you should probably stick with Microsoft's compiler.
Recent Intel compilers achieve significantly better performance on floating-point heavy benchmarks, and are similar to Visual C++ on integer heavy benchmarks. However, it varies dramatically based on the program and whether or not you are using link-time code generation or profile-guided optimization. If performance is critical for you, you'll need to benchmark your application before making a choice. I'd only say that if you are doing scientific computing, it's probably worth the time to investigate.
Intel allows you a month-long free trial of its compiler, so you can try these things out for yourself.
I've been using the Intel C++ compiler since the first Release of Intel Parallel Studio, and so far I haven't felt the temptation to go back. Here's an outline of dis/advantages as well as (some obvious) observations.
Advantages
Parallelization (vectorization, OpenMP, SSE) is unmatched in other compilers.
Toolset is simply awesome. I'm talking about the profiling, of course.
Inclusion of optimized libraries such as Threading Building Blocks (okay, so Microsoft replicated TBB with PPL), Math Kernel Library (standard routines, and some implementations have MPI (!!!) support), Integrated Performance Primitives, etc. What's great also is that these libraries are constantly evolving.
Disadvantages
Speed-up is Intel-only. Well duh! It doesn't worry me, however, because on the server side all I have to do is choose Intel machines. I have no problem with that, some people might.
You can't really do OSS or anything like that on this, because the project file format is different. Yes, you can have both VS and IPS file formats, but that's just weird. You'll get lost in synchronising project options whenever you make a change. Intel's compiler has twice the number of options, by the way.
The compiler is a lot more finicky. It is far too easy to set incompatible project settings that will give you a cryptic compilation error instead of a nice meaningful explanation.
It costs additional money on top of Visual Studio.
Neutrals
I think that the performance argument is not a strong one anymore, because plenty of libraries such as Thrust or Microsoft AMP let you use GPGPU which will outgun your cpu anyway.
I recommend anyone interested to get a trial and try out some code, including the libraries. (And yes, the libraries are nice, but C-style interfaces can drive you insane.)
The last time the company I work for compared the two was about a year ago, (maybe 2). The Intel compiler generated faster code, usually only a bit faster, but in some cases quite a bit.
But it couldn't handle some of the MS language extensions that we depended on, so we ended up sticking with MS. It was VS 2005 that we were comparing it to. And I'm wracking my brain to remember exactly what MS extension the Intel compiler couldn't handle. I'll come back and edit this post if I can remember.
Intel C++ Compiler has AMAZING (human) support. Talking to Microsoft can literally take days. My non-trivial issue was solved through chat in under 10 minutes (including membership verification time).
EDIT: I have talked to Microsoft about problems in their products such as Office 2007, even got a bug reported. While I eventually succeeded, the overall size and complexity of their products and organization hierarchy is daunting.
I'm
interested in different aspects of portability (as you can see when browsing my other questions), so I read a lot about it. Quite often, I read/hear that Code should be written in a way that makes it compilable on different compilers.
Without any real life experience with gcc / g++, it seems to me that it supports every major platform one can imagine, so Code that compiles on g++ can run on almost any system. So why would someone bother to have his code run on the MS Compiler, the Intel compiler and others?
I can think of some reasons, too. As the FAQ suggest, I'll try to post them as an answer, opposed to including them into my own question.
Edit: Conclusion
You people got me completely convinced that there are several good reasons to support multiple compilers. There are so many reasons that it was hard to choose an answer to be the accepted one. The most important reasons for me:
Contributors are much more likely to work an my project or just use it if they can use the compiler of their choice
Being compilable everywhere, being usable with future compilers and tools, and adhering to the standards are enforcing each other, so it's a good idea
On the other hand, I still believe that there are other things which are more important, and now I know that sometimes it isn't important at all.
And last of all, there was no single answer that could convince me not to choose GCC as the primary or default compiler for my project.
Some reasons from the top of my head:
1) To avoid being locked with a single compiler vendor (open source or not).
2) Compiling code with different compilers is likely to discover more errors: warnings are different and different compilers support the Standard to a different degree.
It is good to be compilable on MSVC, because some people may have projects that they build in MSVC that they want to link your code into, without having to set up an entirely different build system.
It is good to be compilable under the Intel compiler, because it frequently compiles faster code.
It is good to be compilable under Clang, because it can give better error messages and provide a better development experience, and it is an easier project to work on than GCC and so may gain additional benefits in the future.
In general, it is good to keep your options open, because there is no one compiler that fits all needs. GCC is a good compiler, and is great for most purposes, but you sometimes need something else.
And even if you're usually only going to be compiling under GCC, making sure your code compiles under other compilers is also likely to help find problems that could prevent your code from working with past and future versions of GCC, for instance, if there's something that GCC is less strict about now, but later adds checks for, another compiler may catch in advance, helping you keep your code cleaner. I've found this helpful in the reverse case, where GCC caught more potential problems with warnings than MSVC did (MSVC is the only compiler we needed to support, as we were only shipping on Windows, but we did a partial port to the Mac under GCC in our free time), which allowed me to produce cleaner code than I would have otherwise.
Portability. If you want your code to be accessible by the maximum number of people possible, you have to make it work on the widest range of possible compilers. It the same idea as make a web site run on browsers other than IE.
Some of it is political. Companies have standards, people have favorite tools etc. Telling someone that they should use X, really puts some people off, and makes it really inaccessible to others.
Nemanja brings up a good point too, targeting for a certain compiler locks you into to using it. In the Open Source world, this might not be as big of a problem (although people could just stop developing on it and it becomes obsolete), but what if the company you buy it from discontinues the product, or goes out of business?
For most languages I care less about portability and more about conforming to international standards or accepted language definitions, from which properties portability is likely to follow. For C, however, portability is a useful idea, because it is very hard to write a program that is "strictly conforming" to the standard. (Why? Because the standards committees felt it necessary to grandfather some existing practice, including giving compilers some freedom you might not like them to have.)
So why try to conform to a standard or make your code acceptable to multiple compilers as opposed to simply writing whatever gcc (or your other favorite compiler) happens to accept?
Likely in 2015 gcc will accept a rather different language than it does today. You would prefer not to have to rewrite your old code.
Perhaps your code might be ported to very small devices, where the GNU toolchain is not as well supported.
If your code compiles with any ANSI C compiler straight out of the box with no errors and no warnings, your users' lives will be easier and your software may be widely ported and used.
Perhaps someone will invent a great new tool for analyzing C programs, refactoring C programs, improving performance of C programs, or finding bugs in C programs. We're not sure what version of C that tool will work on or what compiler it might be based on, but almost certainly the tool will accept standard C.
Of all these arguments, it's the tool argument I find most convincing. People forget that there are other things one can do with source code besides just compile it and run it. In another language, Haskell, tools for analysis and refactoring lagged far behind compilers, but people who stuck with the Haskell 98 standard have access to a lot more tools. A similar situation is likely for C: if I am going to go to the effort of building a tool, I'm going to base it on a standard with a lifetime of 10 years or so, not on a gcc version which might change before my tool is finished.
That said, lots of people can afford to ignore portability completely. For example, in 1995 I tried hard to persuade Linus Torvalds to make it possible to compile Linux with any ANSI C compiler, not just gcc. Linus had no interest whatever—I suspect he concluded that there was nothing in it for him or his project. And he was right. Having Linux compile only with gcc was a big loss for compiler researchers, but no loss for Linux. The "tool argument" didn't hold for Linux, because Linux became so wildly popular; people building analysis and bug-finding tools for C programs were willing to work with gcc because operating on Linux would allow their work to have a big impact. So if you can count on your project becoming a wild success like Linux or Mosaic/Netscape, you can afford to ignore standards :-)
If you are building for different platforms, you will end up using different compilers. Moreover, C++ compilers tend to be always slightly behind the C++ standard, which means they usually change their adherence to it as time passes. If you target the common denominator to all major compilers then the code maintenance cost will be lower.
It's very common for applications (especially open-source application) that other developers would desire to use different compilers. Some would rather be using Visual Studio with MS Compiler for development purposes. Some would rather use Intel compiler for claimed performance benefits and such.
So here are the reasons I can think of
if speed is the biggest concern and there is special, highly optimized compiler for some platforms
if you build a library with a C++ interface (classes and templates, instead of just functions). Because of name mangling and other stuff, the library must be compiled with the same compiler as the client code, and if the client wants to use Visual C++, he must be able to compile the lib with it
if you want to support some very rare platform that does not have gcc support
(For me, those reasons are not significant, since I want to build a library that uses C++ internally, but has a C interface.)
Typically these are the reasons that I've found:
cross-platform (windows, linux, mac)
different developers doing development on different OS's (while not optimal, it does happen - testing usually takes place on the target platform only).
Compiler companies go out of business - or stop development on that language. If you know your program compiles/runs well using another compiler, you've covered your bet.
I'm sure there are other answers as well, but these are the most common reasons I've run into so far.
Several projects use GCC/G++ as a "day-to-day" compiler for normal use, but every so often will check to make sure their code follows the standards with the Comeau C/C++ compiler. Their website looks like a nightmare, and the compiler isn't free, but it's known as possibly the most standards-compliant compiler around, and will warn you about things many compilers will silently accept or explicitly allow as a nonstandard extension (yes, I'm looking at you, Mr. I-don't-mind-and-actually-actively-support-your-efforts-to-do-pointer-arithmetic-on-void-pointers-GCC).
Compiling every so often with a compiler as strict as Comeau (or, even better, compiling with as many compilers as you can get your hands on) will let you know of errors people might experience when trying to compile your code, things your compiler allows you to do that it shouldn't, and potentially things that other compilers don't allow you to do that you should. Writing ANSI C or C++ should be an important goal for code you intend to use on multiple platforms, and using the most standards-compliant compiler around is a good way to do that.
(Disclaimer: I don't have Comeau, and don't plan on getting it, and can't get it because I'm on OS X. I do C, not C++, so I can actually know the whole language, and the average C compiler is much closer to the C standard than the average C++ compiler to the C++ standard, so it's less of an issue for me. Just wanted to put this in here because this started to look like an ad for Comeau. It should be seen more as an ad for compiling with many different compilers.)
This one of those "It depends" questions. For open source code, it's good to be portable to multiple compilers. After all having people in diverse environments build the code is sort of the point.
But for closed source, This is a lot less important. You never want to unnecessarily tie yourself to a specific compiler. But in most of the places I've worked, compiler portability didn't even make into the top 10 of things we cared about. Even if you never use anything other than standerd C/C++, switching a large code base to a new compiler is a dangerous thing to do. Compilers have bugs. Sometimes your code will have bugs that are benign on one compiler, but suddenly a problem on another.
I remember one transition, where one compiler thought this code was just fine:
for (int ii = 0; ii < n; ++ii) { /* some code */ }
for (int ii = 0; ii < y; ++ii) { /* some other code */ }
While the newer compiler complained that ii had been declared twice, so we had to go through all of our code and declare loop variables before the loop in order to switch.
One place I worked was so careful about unintended side effects of compiler switches, that they checked specific compilers into each source tree, and once the code shipped would only use that one compiler to do updates on that code base - forever.
Another place would try out a new compiler for 6 months to a year before they switched over to it.
I find gcc a slow compiler on windows (nothing to compare against under linux). So I (sometimes) want to compile my code under other compilers, just for faster development cycles.
I don't think anyone has mentioned it so far, but another reason may be access to certain platform-specific features: Many operating system vendors have special versions of GCC, or even their own home-grown (or licensed and modified) compilers. So if you want your code to run well on several platforms, you may need to choose the right compiler on each platform. Be that an embedded system, MacOS, Windows etc.
Also, speed may be an issue (both compilation speed and execution speed). Back in the PPC days, GCC produced notoriously slow code on PowerPC CPUs, so Apple put a bunch of engineers on GCC to improve that (GCC was very new for the Mac, and all other PowerPC platforms were small). Platforms that are used less may be optimized less in GCC, so using another compiler that's been written for that platform can be faster.
But as a final summary: While there is ideal value in compiling on several compilers, in practice, this is mainly interesting for cross-platform software (and open-source software, because it often gets made cross-platform fairly quickly, and contributors have it easier if they can use their compiler of choice instead of having to learn a new one). If you need to ship on one platform only, shipping and maintenance are usually much more important than investing in building on several compilers if you're only releasing the builds made with one of them. However, you will want to clearly document any deviations from the standard (GCC-isms, for instance) to make the job of porting easier, should you ever have to do it.
Both Intel compiler and llvm are faster than gcc. The real reasons to use gcc are
Infinite hardware support (on no other compiler can you compile a lego mindstorm code on your old DEC).
it's cheap
best spagety optimizer in the business.
I have been using gcc, g++ for my C, C++ application development till now and have found it to be amazing. But browsing through Stack Overflow I found many members stating that error reporting in Comeau compiler is much more than any other compiler. Is this true? I haven't invested in any commercial release of a compiler. Is it really worth spending money on a commercial release of a C/C++ compiler when gcc, g++ are doing the trick?
My experience with writing C++ is that compiling your code with more than one compiler is a great way to find odd corner-cases in your code. In our case, we've used gcc, Apple gcc, and the Visual Studio compiler cl (which is free). When on Windows, I prefer the cl compiler since it compiles faster (around five times faster for us) and it produces better code (around 30% faster last time I checked). Which compiler produces the fastest code is always dependent on the application though. In our particular case the Intel compiler is not so good at producing fast code contrary to popular opinion, so there is no real incentive to use it.
If we had the money to spend, compiling with Comeau would be nice to help with additional checking for standards conformance. Apart from that, I'm happy with the compilers we use.
The killer feature of the Comeau compiler is its conformance (including C++03!) and excellent error reporting.
There's an online way to try it out too: http://www.comeaucomputing.com/tryitout/
The Comeau compiler is definitely worth it if these features are worth it to you.
Hats off to the Comeau compiler!
There are three main use of Comeau's compiler:
targeting platforms having only a C compiler
having an additional compiler with good conformance reputation and good error message
experimenting with features which are available only with it (experimenting with exported templates was my reason to buy it years ago for instance)
Note that debugging is not one of the use. It generates C code which is then compiled by your C compiler. It use #line directives so that you are able to go step by step in your code, but to do more, you'll have the same problem as when debugging any language using C as intermediate language: the debugger is not aware of the convention of the starting language.
If you're happy with gcc tools, stick with them. Don't fix what's not broken. They're being used daily by lots of people, and they're certainly pretty good.
That said, gcc has been criticized for "getting slower with each release and creating crappy code". Don't know about the "crappiness", but we've been compiling time-critical sections with hardware vendor specific (e.g. Intel) compilers. They indeed create way faster code in some cases, compared to what gcc achieves. But usually the difference doesn't matter, though.
I would tend to say no, g++ is a great compiler with a huge community supporting it, there really isn't any need to switch over to a commercial compiler unless you want the support it offers, which unless you're a large developer you probably don't. With g++ and VS Express on windows, there really isn't any need to dish out money for a compiler. Better places to spend your money/time!
I believe that Comeau Release version is pretty stable. When you buy commercial C/C++ compiler you'll pay mostly for specific features. You should decide whether you need those features.
If you don't have special requirements GNU C/C++ compiler is a great choice.