I am trying out the sse2 support in fpc 2.1.1 and compile my code with -Cfsse2.

The program is the mandelbrot benchmark:
http://shootout.alioth.debian.org/gp4/benchmark.php?test=mandelbrot&lang=fpascal

The innerloop is like this:
       Zr := 0;  Zi := 0; Tr := 0; Ti := 0;
       i := 0;
       while (i<50) and (Tr + Ti< limit) do begin
         inc(i);
         Zi := 2*Zr*Zi + Ci;
         Zr := Tr - Ti + Cr;
         Ti := Zi * Zi;
         Tr := Zr * Zr;
       end;

If I look at the generated assembler, I noticed that only %xmm0 is used and all each time the variable needs to be retrieved from the stack.

# Var Zr located in register mreg0md
# Var Zi located in register mreg0md
# Var Ti located in register mreg0md
# Var Tr located in register mreg0md
# Var Cr located in register mreg0md
# Var Ci located in register mreg0md

...

# [33] Zr := Tr - Ti + Cr;
movsd -88(%ebp),%xmm0
subsd -80(%ebp),%xmm0
addsd -96(%ebp),%xmm0
movsd %xmm0,-112(%ebp)
# [34] Ti := Zi * Zi;
movsd -72(%ebp),%xmm0
mulsd -72(%ebp),%xmm0
movsd %xmm0,-80(%ebp)

I thought there were more than one xmm registers. Why aren't they used?

Vincent

They are not used, because the same body contains a procedure call and the %xmm0 registers are volatile. See also the notes with issue 7533: http://www.freepascal.org/mantis/view.php?id=7533

Vincent

Op Fri, 6 Oct 2006, schreef Vincent Snijders:

They are not used, because the same body contains a procedure call and the %xmm0 registers are volatile. See also the notes with issue 7533: http://www.freepascal.org/mantis/view.php?id=7533

This is solveable with SSA, so a variable can be in a register in one part of the procedure and in memory in another part of the procedure. It should be a matter of being patient.

Daniël

Yes, that is the reason, why the issue is still open after the explanation.

Do you have an idea if SSA with program control structures is a planned for 2.2.0 or later(2.4.0)?

Vincent

Op Fri, 6 Oct 2006, schreef Vincent Snijders:

I think it will become 2.4.0, but it might depend on the release schedule of 2.2.0.

Daniël