Gcc compiler advantage and disadvantage of gcc

Gcc compiler advantage and disadvantage of gcc

[i.98shaikhh]

Plzz

Re: Gcc compiler advantage and disadvantage of gcc

[Anna Szekér]

Witch compiler would you compare it to?

2016-08-18 14:01 GMT+02:00, i.98shaikhh <i.98shaikhh@gmail.com>:
> Plzz

Re: Gcc compiler advantage and disadvantage of gcc

[Dennis Clarke]

On 08/18/2016 02:24 PM, Anna Szekér wrote:
> Witch compiler would you compare it to?

A reasonable comparison would be the Oracle Studio 12.5 compiler which
creates wonderfully optimal code on both Sparc and x86 architectures.

Dennis

Re: Re: Gcc compiler advantage and disadvantage of gcc

[Manuel López-Ibáñez]

On 18/08/16 19:29, Dennis Clarke wrote:
> On 08/18/2016 02:24 PM, Anna Szekér wrote:
>> Witch compiler would you compare it to?
>
> A reasonable comparison would be the Oracle Studio 12.5 compiler which
> creates wonderfully optimal code on both Sparc and x86 architectures.

If somebody writes a nice comparison in the style of 
http://clang.llvm.org/comparison.html

I'll format it for the GCC wiki for others to find.

Cheers,
	Manuel.

Re: Gcc compiler advantage and disadvantage of gcc

[Andrew Haley]

On 18/08/16 19:37, Manuel López-Ibáñez wrote:
> On 18/08/16 19:29, Dennis Clarke wrote:
>> On 08/18/2016 02:24 PM, Anna Szekér wrote:
>>> Witch compiler would you compare it to?
>>
>> A reasonable comparison would be the Oracle Studio 12.5 compiler which
>> creates wonderfully optimal code on both Sparc and x86 architectures.
> 
> If somebody writes a nice comparison in the style of 
> http://clang.llvm.org/comparison.html

But hopefully slightly less self serving.

Andrew.

Re: Gcc compiler advantage and disadvantage of gcc

[Manuel López-Ibáñez]

On 19/08/16 09:25, Andrew Haley wrote:
> On 18/08/16 19:37, Manuel López-Ibáñez wrote:
>> On 18/08/16 19:29, Dennis Clarke wrote:
>>> On 08/18/2016 02:24 PM, Anna Szekér wrote:
>>>> Witch compiler would you compare it to?
>>>
>>> A reasonable comparison would be the Oracle Studio 12.5 compiler which
>>> creates wonderfully optimal code on both Sparc and x86 architectures.
>>
>> If somebody writes a nice comparison in the style of
>> http://clang.llvm.org/comparison.html
>
> But hopefully slightly less self serving.

To be honest, it doesn't seem an unfair characterization to me.

GCC could highlight the ethical and tit-for-tat benefits of the GPL, but I 
guess they do not see those as a benefit.

GCC has also the benefit of being a more mature code base and, as a result,  it 
has been more thoroughly tested in a wider range of codes; yet this is 
difficult to quantify and arguably Clang is more widely used today than GCC, 
just not in Linux, thus this might not be true anymore.

Is there anything else there that you think is misleading or plain wrong?

Cheers,

	Manuel.

Re: Gcc compiler advantage and disadvantage of gcc

[Tim Prince]

On 8/19/2016 10:19 AM, Manuel López-Ibáñez wrote:
> On 19/08/16 09:25, Andrew Haley wrote:
>> On 18/08/16 19:37, Manuel López-Ibáñez wrote:
>>> On 18/08/16 19:29, Dennis Clarke wrote:
>>>> On 08/18/2016 02:24 PM, Anna Szekér wrote:
>>>>> Witch compiler would you compare it to?
>>>>
>>>> A reasonable comparison would be the Oracle Studio 12.5 compiler which
>>>> creates wonderfully optimal code on both Sparc and x86 architectures.
>>>
>>> If somebody writes a nice comparison in the style of
>>> http://clang.llvm.org/comparison.html
>>
>> But hopefully slightly less self serving.
>
> To be honest, it doesn't seem an unfair characterization to me.
>
> GCC could highlight the ethical and tit-for-tat benefits of the GPL,
> but I guess they do not see those as a benefit.
>
> GCC has also the benefit of being a more mature code base and, as a
> result,  it has been more thoroughly tested in a wider range of codes;
> yet this is difficult to quantify and arguably Clang is more widely
> used today than GCC, just not in Linux, thus this might not be true
> anymore.
>
> Is there anything else there that you think is misleading or plain wrong?
>
I have the impression that clang supports OpenMP on linux but not
Windows (where gcc drops a few OpenMP features).

-- 
Tim Prince

Re: Gcc compiler advantage and disadvantage of gcc

[Andrew Haley]

On 19/08/16 15:19, Manuel López-Ibáñez wrote:
> On 19/08/16 09:25, Andrew Haley wrote:
>> On 18/08/16 19:37, Manuel López-Ibáñez wrote:
>>> On 18/08/16 19:29, Dennis Clarke wrote:
>>>> On 08/18/2016 02:24 PM, Anna Szekér wrote:
>>>>> Witch compiler would you compare it to?
>>>>
>>>> A reasonable comparison would be the Oracle Studio 12.5 compiler which
>>>> creates wonderfully optimal code on both Sparc and x86 architectures.
>>>
>>> If somebody writes a nice comparison in the style of
>>> http://clang.llvm.org/comparison.html
>>
>> But hopefully slightly less self serving.
> 
> To be honest, it doesn't seem an unfair characterization to me.
> 
> GCC could highlight the ethical and tit-for-tat benefits of the GPL, but I 
> guess they do not see those as a benefit.

It says:

"GCC is licensed under the GPL license. clang uses a BSD license, which
allows it to be embedded in software that is not GPL-licensed."

Note that GCC "is licensed under" the GPL licence" whereas clang
"uses" a BSD licence.  Why not say that GCC uses the GPL licence?

I could just as much write "GCC uses the GPL license.  clang uses a
BSD license, which allows evil bastard proprietary software companies
to take the free and open code of clang and release and sell versions
with licence restrictions but no source code."  and put that in the
"Pro's of GCC vs clang" section.  I urge them to say so and will be
happy to allow them to use that sentence without even requiring any
attribution!

> GCC has also the benefit of being a more mature code base and, as a
> result, it has been more thoroughly tested in a wider range of
> codes; yet this is difficult to quantify and arguably Clang is more
> widely used today than GCC, just not in Linux, thus this might not
> be true anymore.
> 
> Is there anything else there that you think is misleading or plain
> wrong?

It's fair to point out that clang is faster, but "much" faster is an
opinion.  Most of the "Pro's of clang vs GCC" are design decisions
which may well be of interest to the maintainers but don't affect
users who just want a compiler.  Of course the authors of clang think
their design decisions are better and they're prepared to defend them.
But an observer who was trying hard to be neutral would describe them
as differences.

Andrew.

Re: Gcc compiler advantage and disadvantage of gcc

[Jeffrey Walton]

>> But hopefully slightly less self serving.
>
> To be honest, it doesn't seem an unfair characterization to me.
>
> GCC could highlight the ethical and tit-for-tat benefits of the GPL, but I
> guess they do not see those as a benefit.
>
> GCC has also the benefit of being a more mature code base and, as a result,
> it has been more thoroughly tested in a wider range of codes; yet this is
> difficult to quantify and arguably Clang is more widely used today than GCC,
> just not in Linux, thus this might not be true anymore.

GCC does a much better job of optimizing. I run benchmarks for some
libraries regularly to ensure there are no regressions. GCC is
consistently 2x faster than Clang, and GCC is on-par with ICC.

It seems the slow-down is the treatment of const-expr's. Under the
laws of the physical universe as we know them, some values are fixed
at compile time won't change (regardless of their const-expr status).
GCC optimizes them (common sense), while Clang does not (expected to
somehow change).

That little slow down adds up, and it makes us do things like avoid
std::numeric_limits<T>::max() in favor of a #define instead. More
complex examples include propagating a constant using a template
parameter instead of a function parameter. GCC will realize a constant
does not change under the laws of the physical universe as we know
them; while Clang will treat the constant passed as a parameter as
something that can miraculously change after saving the source file.

Jeff

Re: Gcc compiler advantage and disadvantage of gcc

[Tim Prince]

On 8/19/2016 2:09 PM, Jeffrey Walton wrote:
>>> But hopefully slightly less self serving.
>> To be honest, it doesn't seem an unfair characterization to me.
>>
>> GCC could highlight the ethical and tit-for-tat benefits of the GPL, but I
>> guess they do not see those as a benefit.
>>
>> GCC has also the benefit of being a more mature code base and, as a result,
>> it has been more thoroughly tested in a wider range of codes; yet this is
>> difficult to quantify and arguably Clang is more widely used today than GCC,
>> just not in Linux, thus this might not be true anymore.
> GCC does a much better job of optimizing. I run benchmarks for some
> libraries regularly to ensure there are no regressions. GCC is
> consistently 2x faster than Clang, and GCC is on-par with ICC.
>
> It seems the slow-down is the treatment of const-expr's. Under the
> laws of the physical universe as we know them, some values are fixed
> at compile time won't change (regardless of their const-expr status).
> GCC optimizes them (common sense), while Clang does not (expected to
> somehow change).
>
> That little slow down adds up, and it makes us do things like avoid
> std::numeric_limits<T>::max() in favor of a #define instead. More
> complex examples include propagating a constant using a template
> parameter instead of a function parameter. GCC will realize a constant
> does not change under the laws of the physical universe as we know
> them; while Clang will treat the constant passed as a parameter as
> something that can miraculously change after saving the source file.
>
> Jeff
There are many situations where gcc optimizes better, and a few where
clang is better.  Among the latter is min|
max reduction, where clang can "riffle" by batching more than one simd
parallel reduction so as to overcome latency.  The implied point is
valid, that many users can suffer a little more compile time in order to
improve run time.

-- 
Tim Prince