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D.gnu - Inexplicable LDC vs GDC speed difference

reply Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
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?
Feb 13 2013
parent reply "jerro" <a a.com> writes:
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.
Feb 13 2013
next sibling parent Johannes Pfau <nospam example.com> writes:
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.
Feb 14 2013
prev sibling parent reply Johannes Pfau <nospam example.com> writes:
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
Feb 19 2013
next sibling parent Joseph Rushton Wakeling <joseph.wakeling webdrake.net> writes:
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



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++.
Feb 22 2013
prev sibling parent Iain Buclaw <ibuclaw ubuntu.com> writes:
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>



 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';
Feb 22 2013