Hi Torsten,
The reason why it's not compiling correctly with -a is because the
operand size is being set to S_XMM, not S_YMM (because it's going by the
size of the source operand), so when writing the .s files, it adds an
'x' suffix to the end of the opcode.
I know there's a high risk of it
Ah crumbs, I thought it was too easy! I can't believe I missed the
obvious there! Not much of a saving if it has to store the return
address somewhere (mov @return(%rip),%rcx; mov %rcx, (somewhere on the
stack)).
The advantage would be reducing the chance of additional memory caching
since
Ah brilliant, thank you.
I have used Agner Fog's material before for cycle counting. When I
implemented my 3 MOV -> XCHG optimisation
(https://bugs.freepascal.org/view.php?id=36511), I used Agner Fog's
empirical results to determine when it's best to apply this optimisation
where speed is co
In the meantime, I've uploaded the patch to the bug report after
confirming that all tests on x86_64-win64 have passed with no
regressions: https://bugs.freepascal.org/view.php?id=37785
Other platforms and AVX-512-specific code still need testing though.
Gareth aka. Kit
On 02/10/2020 07:59,
So... I've done some tests, replacing TEST RCX, $4 with TEST CL, $4 and
the like in a number-crunching function, and it seems to cause a notable
penalty, even though none of the instructions are in my critical loop.
So I think it's something that needs to be avoided in most cases. I
think the
Confirmed my suspicions. if I zero the upper bits of the register (I
used something akin to "AND RCX, $F"), there is no speed loss.
Therefore, I can make the hypothesis, on my Intel(R) Core(TM) i7-10750H,
that using TEST on a sub-register causes a false dependency if the bits
outside of the s
On 10/2/20 2:13 PM, J. Gareth Moreton via fpc-devel wrote:
Confirmed my suspicions. if I zero the upper bits of the register (I
used something akin to "AND RCX, $F"), there is no speed loss.
Therefore, I can make the hypothesis, on my Intel(R) Core(TM)
i7-10750H, that using TEST on a sub-reg
Sure, I can send you something. It might have to be to a personal
e-mail though depending on how big the attachments are. Watch this space.
I may be a bit of a mad scientist when it comes to my testing and
research (and sometimes I make a stupid mistake like with the recent
nested function pr
