Slowdown of C code when inline assembler is used

[kobold]

Hi again! After a long period of inactivity i am back again. 

Today i discovered a strange behavior. And that's why i wrote this topic.

In a test application i was using inline assembler to make a benchmark between C and ASM.
The ASM part was several times faster (to my surprise - because i am not an experienced ASM coder).

But now there is a thing i do not understand:
The speed of the C part increased dramatically (about between 2 and 4 times) when i commented the ASM Parts out.
Suddenly the C part reached or beaten the speed of the ASM code!

More strangeness:
Even when i include only some sort of ASM nonsense code somewhere in the C code, the behavior was the same.
For example i inserted this at the end of the program before the "return(0);":

Code: [Select]

_asm push ax
_asm pop ax
or even better :

Code: [Select]

_asm nop

As a result the speed of the C code dropped dramatically again.

Settings: Console application, x86, no debugging.
The problem occurs only if some sort of compiler optimization is activated.
Without optimization the speed stays the same - with or without inline ASM.
My version(s):

Code: [Select]

RSRC0007.DLL: Version 5.00.2
SUPPORT.DLL: Version 5.00.1
POCFMT.DLL: Version 5.00.0
PORC.DLL: Version 5.00.0
POBR.DLL: Version 5.00.1
SQLITE3.DLL: Version 3.5.3
POCC.EXE: Version 5.00.11
POASM.EXE: Version 5.00.3
POLINK.EXE: Version 5.00.0
IDESPAWN.EXE: Version 5.00.0


[Vortex]

Hi kobold,

Inline assembly can interfere with the C code optimization. You should move the assembly routine to a separate module, assemble it with Poasm and then link the object module with the main project module.

[kobold]

Ok - i'll try it