Florian Klaempfl schreef:
Line 17 generates two assembler instructions. Line 22 generates three
assembler instructions. As far as I can see both high(d) and @d[high(d)]
are constants, because d is a global variable.
Is it possible that line 22 will generate 2 assembler instructions in
the future? Or is this a limitation of the i386 assembler? Or do I make
a mistake in my reasoning?
No, you aren't, however, the problem of this benchmark are the inserted fwaits
which are necessary to get fpu exceptions at correct lines. The best would be to
introduce a switch which prevents the fwaits.
Aha, that explains why explicit subexpression elimination fails too.
using comon expression, less calculations:
distance:=sqrt(sqr(dx)+sqr(dy)+sqr(dz));
mag := dt / (distance*distance*distance);
but this is faster:
distance:=sqrt(sqr(dx)+sqr(dy)+sqr(dz));
mag := dt / (sqrt(sqr(dx)+sqr(dy)+sqr(dz))*(sqr(dx)+sqr(dy)+sqr(dz)));
using comon expression, less calculations:
b1mag := b1^.mass * mag;
b2^.vx := b2^.vx + dx * b1mag;
b2^.vy := b2^.vy + dy * b1mag;
b2^.vz := b2^.vz + dz * b1mag;
but this is faster:
b2^.vx := b2^.vx + dx * b1^.mass * mag;
b2^.vy := b2^.vy + dy * b1^.mass * mag;
b2^.vz := b2^.vz + dz * b1^.mass * mag;
Vincent
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