Re: Optimizer? What optimizer?

[Stefan Monnier]

>> Is there some fundamental reason defsubst does so poorly here compared
>> to defmacro?

Basically you're comparing

  (if nil b (1+ b))

against

  (let ((a nil) (b b)) (if a b (1+ b)))

The byte-compiler performs approximately zero analysis to try and figure
out what is the value of a variable at a given moment (i.e. none of
"constant propagation", "variable propagation", "data flow analysis",
"abstract interpretation").  So it doesn't realize that `a' has value
nil when passed to `if'.
The "optimizer" is very naive (even tho we have two optimization
phases: one working on the Elisp code after macro-expansion and another
working on the byte-code), indeed.


        Stefan