🚀 go-pugleaf

In article <1458@exodus.Eng.Sun.COM> chased@rbbb.Eng.Sun.COM (David Chase) writes:
> (AND, the optimizer will optimize for
> different machines, unlike the manual optimizer).

quickpick would remedy that, permanently.

> How often do you
> catch an optimizer bug, and often do you make a mistake
> hand-optimizing code?

First releases of optimizers simply don't work; after they've spent a
few years on the market, their bugs are few and far between. Maybe one
bug per ten thousand lines of code, after a year of maturity. It goes
down quickly past that.

I do not remember ever making a mistake in hand optimization by the most
fundamental standard technique: adding variable x to keep track of some
intermediate quantity, and eliminating redundant variables given x. What
optimizer can do this for any but the most primitive intermediate
expressions? (Introducing a pointer to traverse an array, and
eliminating the index that it replaces, is the simplest example.)

It would be interesting to see a language where you could say ``Okay,
keep 4*k + j - foo(i) in a register, and use it wherever possible.''
Somehow I don't think we have the technology yet.

  [ example of code: 30x faster from better algorithms, etc., in ]
  [ several weeks, 1.7x faster from optimizer in a couple of minutes ]

But I can usually get another 2x to 5x out of lots of ``picky'' hand
optimizations, having nothing to do with the algorithms. And I'm not
going to introduce subtle bugs in weird cases with unsafe program
transformations.

---Dan