Vincent Snijders schreef:
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?
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
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