On 2010-10-15 01:22, Sean Kelly wrote:
Jacob Carlborg Wrote:
Thread.getThis() calls pthread_getspecific which is just three
instructions on Mac OS X, so I guess that's not why it's so slow. The
only thing I can think of is first moving the if statement into the
assert and then trying to inline as much of the function calls.
Swapping the assert and the executable code would save you a jump, but inlining
the call to ___tls_get_addr would be be a bit trickier. We'd probably have to
expose Thread.sm_this as an extern (C) symbol, move the function to object.d
and explicitly do the pthread_getspecific call there. If that would be enough
for the compiler to inline the calls then it shouldn't be too hard to test, but
I'm worried that the call generation may happen too late. I guess it wouldn't
be too hard to figure out from looking at the asm output though (PIC code
weirdness notwithstanding).
I think it would save more than just a jump. When compiling in release
mode the compiler have to generate code for the if statement but with an
assert it can just skip it. See the assembly at the bottom.
I was thinking about inlining Thread.getThis() as a first step. Then
inlining pthread_getspecific as a second step. I don't know if we can
inline pthread_getspecific due to license issues but at least there is
an inline version available. Then of course inlining the call to
__tls_get_addr could help as well.
Both of the following versions are compiled with "dmd -c -O -release".
___tls_get_addr in thread.d compiled with if statement:
___tls_get_addr:
push EBP
mov EBP,ESP
push EAX
mov EDX,EAX
push EBX
call L2000
L2000: pop EBX
cmp 03AAh[EBX],EDX
ja L2011
cmp 03AEh[EBX],EDX
ja L2012
L2011: hlt
L2012: mov -4[EBP],EDX
call L217E
mov EAX,054h[EAX]
add EAX,-4[EBP]
sub EAX,03AAh[EBX]
pop EBX
mov ESP,EBP
pop EBP
ret
nop
22 lines for the above code, the same compiled with an assert instead:
___tls_get_addr:
push EBP
mov EBP,ESP
sub ESP,8
mov -4[EBP],EAX
call L216E
mov EAX,054h[EAX]
add EAX,-4[EBP]
call L200D
L200D: pop ECX
sub EAX,038Dh[ECX]
mov ESP,EBP
pop EBP
ret
This is just 13 lines of code, I can tell you that I don't know assembly
but I can see the number of instructions are a lot more in the version
with the if statement than the one with the assert.
--
/Jacob Carlborg
