On 2017-07-02 02:41 AM, Steven D'Aprano wrote:
On Sat, Jul 01, 2017 at 07:52:55PM -0300, Soni L. wrote:
On 2017-07-01 07:34 PM, Victor Stinner wrote:
Let's say that you have a function "def mysum (x; y): return x+y", do
you always want to use your new IADD instruction here? What if I call
mysum ("a", "b")?
Victor
Let's say that you do. Given how short it is, it would just get inlined.
Your call of mysum ("a", "b") would indeed not use IADD, nor would it be
a call. It would potentially not invoke any operators, but instead get
replaced with "ab".
What you are describing sounds more like the output of a keyhole
optimizer that folds constants, only extended to look inside functions.
I expect that it would have to be a VERY clever optimizer, since it
would have to do a complete whole-of-program static analysis to be sure
that mysum has not been replaced, shadowed or redefined by the time it
is called.
Runtime. Not static. This is the same kind of stuff LuaJIT (and any
other JIT) does.
I won't say that is outright impossible, but it would be *extremely*
hard to do something like that at compile time.
When you have a tracing JIT, you can do away with a lot of overhead. You
can inline functions, variables, do away with typechecks, and many other
things. This holds true even if that JIT never emits a single byte of
machine code.
What you are describing sounds more like an "Ahead Of Time" (AOT)
compiler to me. Especially the part about doing away with typechecks. As
far as I know you can really only do away with typechecks or other
guards if you know ahead of time (at compile time) what the types of
values are, and that requires static typing.
You can do that at runtime with a JIT and flushing the JIT cache when
your assumptions (guards) change. (altho in reality you wouldn't flush
the whole JIT cache because that'd be expensive.)
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