That's great to hear! Glad to help.

For functions with no stack frame, the
compiler simply puts RET at the very end
of the routine and is all that's needed.
For functions with a stack frame, either
LEAVE or MOV RSP, RBP; POP RBP must
precede it. The optional parameter after
RET is the number of bytes allocated to
the stack by parameters that aren't in
registers.

So what happens now? Do we submit a patch?

Gareth aka. Kit

It's not quite that simple, at least under windows: https://docs.microsoft.com/en-us/cpp/build/prolog-and-epilog

But yes, this documents that there can be multiple epilogues, so the additional ret would be fine in this regard.

Following this exact format is required so that the stack unwinder during processing of SEH (structured exception handling) which is performed by the OS can correctly restore the value of non-volatile registers that has been saved on the stack.

Fortunately, as our function in this case doesn't use the stack at all and doesn't contain calls to other functions, this can be skipped.

So what happens now? Do we submit a patch?

I think Sven Barth was going to fix this up anyway?

Cheers,
Thorsten

Hi Florian.  Thorsten and I got down to a fairly optimised version of Frac, in both speed and size:

****

function Frac(const X: ValReal): ValReal; assembler; nostackframe; asm
  movq      rax,  xmm0
  shr       rax,  48
  and       ax,   $7FF0
  cmp       ax,   $4330
  jge       @@zero
  cvttsd2si rax,  xmm0
  cvtsi2sd  xmm4, rax
  subsd     xmm0, xmm4
  ret
@@zero:
  xorpd     xmm0, xmm0
end;

****

It fits into just three 16-byte blocks and is the fastest overall from our tests, although there's a slight penalty if it jumps to @@zero that seems to be architecture-dependent (e.g. it slows down for me, but Thorsten didn't see much). Aligning @@zero to a 16-byte boundary may fix this for some, but it doesn't for me.  Oh the joy of processor intracacies!

Gareth aka. Kit.

On Sun 29/04/18 19:28 , Florian Klaempfl sent:

Can you take a look at the generated machine code if delphi uses proper multi byte nops. If not, the align might make things indeed worse.