[Issue 4383] Optimizer doesn't keep floating point values on the stack if used more than once

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http://d.puremagic.com/issues/show_bug.cgi?id=4383



--- Comment #4 from Don <clugdbug at yahoo.com.au> 2010-06-25 09:32:15 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> > (In reply to comment #1)
> > > Sounds like a prime case for a keyhole optimization. Does DMD have the
> > > infrastructure in place to do that?
> > 
> > Yes, there's pinholeopt() in cod3.c. But this optimisation should be done
> > earlier.
> 
> Agreed, but (done wrong now) + (done right later) > (done right later)
> 
> > Although it seems as though you could replace:
> > fstp XXX; fld XXX;  with fst XXX; there's unfortunately no fst instruction for
> > 80-bit reals, and for doubles and floats it can change the rounding.
> 
> I was primarily thinking of removing total nop cases (store+load+never used
> again). 

That's why it needs to be done earlier. pinhole doesn't know if values are used
again.

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