February 13, 2013
Following some code posted in d.learn, I've observed a bizarre and (to me) inexplicable difference in code speed depending on whether LDC or GDC is used as the compiler:
http://forum.dlang.org/post/mailman.1239.1360764028.22503.digitalmars-d-learn@puremagic.com

I'm using latest-from-GitHub versions of both compilers, compiled as release versions.

Anyone have any idea what could be the source of the speed difference?
February 14, 2013
On Wednesday, 13 February 2013 at 15:07:04 UTC, Joseph Rushton Wakeling wrote:
> Following some code posted in d.learn, I've observed a bizarre and (to me) inexplicable difference in code speed depending on whether LDC or GDC is used as the compiler:
> http://forum.dlang.org/post/mailman.1239.1360764028.22503.digitalmars-d-learn@puremagic.com
>
> I'm using latest-from-GitHub versions of both compilers, compiled as release versions.
>
> Anyone have any idea what could be the source of the speed difference?

The speed difference is partly caused by the fact that GDC doesn't inline juliaFunction and squarePlusMag. I have a build of GDC with always_inline attribute enabled (I just copied a few lines of code from some old version of GDC to d-builtins.c of a recent version), so I tried adding pragma(attribute, always_inline) to those functions. It seems that GDC is unable to inline them for some reason.

When I added always_inline to juliaFunction, I got this error:

error: inlining failed in call to always_inline ?main.Julia!(float).juliaFunction?: function body can be overwritten at link time

Here's reduced code that gives the same error when always_inline is added to bar:

int bar()(int x)
{
    if (x)
        return 0;

    return 1;
}

int foo(int a)
{
    return bar( a);
}

bar can be inlined if I remove the first pair of parentheses (so that it isn't a template).



When I add always_inline to squarePlusMag I get:

error: inlining failed in call to always_inline ?main.Julia!(float).ComplexStruct.squarePlusMag?: mismatched arguments

Reduced code that gives the same error when always_inline is added to bar:

struct S
{
    int bar(const S s)
    {
        return 0;
    }
}

int foo()
{
    S s;
    return s.bar(s);
}

bar can be inlined if I remove const.

I have compiled all the samples with -c -O3 -finline-functions -frelease.
February 14, 2013
Am Thu, 14 Feb 2013 01:18:21 +0100
schrieb "jerro" <a@a.com>:

> 
> When I added always_inline to juliaFunction, I got this error:
> 
> error: inlining failed in call to always_inline ?main.Julia!(float).juliaFunction?: function body can be overwritten at link time
> 
> Here's reduced code that gives the same error when always_inline is added to bar:
> 
> int bar()(int x)
> {
>      if (x)
>          return 0;
> 
>      return 1;
> }
> 
> int foo(int a)
> {
>      return bar( a);
> }
> 
> bar can be inlined if I remove the first pair of parentheses (so that it isn't a template).
> 

I'll have a look at this soon. I already have an idea what could be wrong.

> 
> When I add always_inline to squarePlusMag I get:
> 
> error: inlining failed in call to always_inline ?main.Julia!(float).ComplexStruct.squarePlusMag?: mismatched arguments
> 
> Reduced code that gives the same error when always_inline is added to bar:
> 
> struct S
> {
>      int bar(const S s)
>      {
>          return 0;
>      }
> }
> 
> int foo()
> {
>      S s;
>      return s.bar(s);
> }
> 
> bar can be inlined if I remove const.
> 
> I have compiled all the samples with -c -O3 -finline-functions -frelease.


February 19, 2013
Am Thu, 14 Feb 2013 01:18:21 +0100
schrieb "jerro" <a@a.com>:

> On Wednesday, 13 February 2013 at 15:07:04 UTC, Joseph Rushton
> Wakeling wrote:
> 
> Here's reduced code that gives the same error when always_inline is added to bar:
> 
> int bar()(int x)
> {
>      if (x)
>          return 0;
> 
>      return 1;
> }
> 
> int foo(int a)
> {
>      return bar( a);
> }
> 
> bar can be inlined if I remove the first pair of parentheses (so that it isn't a template).

https://github.com/D-Programming-GDC/GDC/pull/50


> 
> struct S
> {
>      int bar(const S s)
>      {
>          return 0;
>      }
> }
> 
> int foo()
> {
>      S s;
>      return s.bar(s);
> }
> 
> bar can be inlined if I remove const.
> 
> I have compiled all the samples with -c -O3 -finline-functions -frelease.

I posted this to our bugzilla, I'm not sure if I'll have the time to look at this one.

http://gdcproject.org/bugzilla/show_bug.cgi?id=37
February 22, 2013
On 02/19/2013 09:34 AM, Johannes Pfau wrote:
> I posted this to our bugzilla, I'm not sure if I'll have the time to
> look at this one.
>
> http://gdcproject.org/bugzilla/show_bug.cgi?id=37

Just to note -- with your pull request #50 now included in GDC, things speed up very slightly.  Removing the const from the Julia value code, results become comparable to g++ and the C++ implementation (i.e. about 4.3 s for the 'double' case).

LDC still produces a faster executable for this particular code, but then, clang++ also produces a faster executable than g++.
February 22, 2013
On 22 February 2013 18:59, Joseph Rushton Wakeling < joseph.wakeling@webdrake.net> wrote:

> On 02/19/2013 09:34 AM, Johannes Pfau wrote:
>
>> I posted this to our bugzilla, I'm not sure if I'll have the time to look at this one.
>>
>> http://gdcproject.org/**bugzilla/show_bug.cgi?id=37<http://gdcproject.org/bugzilla/show_bug.cgi?id=37>
>>
>
> Just to note -- with your pull request #50 now included in GDC, things speed up very slightly.  Removing the const from the Julia value code, results become comparable to g++ and the C++ implementation (i.e. about 4.3 s for the 'double' case).
>
> LDC still produces a faster executable for this particular code, but then, clang++ also produces a faster executable than g++.
>


Cool, cheers for checking.


-- 
Iain Buclaw

*(p < e ? p++ : p) = (c & 0x0f) + '0';


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