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/[email protected]
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.
