Lucas Dixon wrote:
Some answers to my own questions...
saves only 1MB, despite the fact that I have many deeply nested functors
in my code. Changing the max inline depth also seems to have pretty much
no change on the size of generated code.... so now I still wonder how I
got 20MB of compiled code, but at least its not 200 :)
I'd be interested to know why this is so large, and whether this is
really code or some other data.
I'm surprised that shareCommonData was so effective as I had almost only
functions... does shareCommonData share functions that are the same?
(David: I think I remember you telling me it did not - but I can't
remember why...?)
No, it doesn't. The reason is that, on the i386 at least, code segments
contain PC-relative calls and jumps. That means that two pieces of code
that look the same may well be calling different functions and so can't
be merged and equally two pieces that actually call the same function
wouldn't appear to be the same.
I was thinking about calling PolyML.shareCommonData on every defined
value - would this do more than on PolyML.rootFunction ? or does
polyml already ignore unused functions?
PolyML.shareCommonData detects any sharing between values that are
reachable from its argument. PolyML.rootFunction is the function that
is called when Poly/ML starts up and includes references to the global
name space. So calling PolyML.shareCommonData PolyML.rootFunction will
detect all the possible sharing within declarations you have made.
Crucially, it detects sharing within the data structures the compiler
uses to represent type-information so it reduces the space needed to
store information about structures, signatures and functors.
Calling PolyML.shareCommonData again on particular values won't help.
If something is completely unreachable then it will be thrown away by
the garbage-collector.
What happens to exceptions which are raise after
PolyML.Compiler.forgetXXX where the exception would normally contain
type-names ? are they also forgotten?
it appears that the data associated with exceptions is simply not printed.
Exception packets contain an identifier for the exception and the name
of the exception but do not otherwise contain any type information.
When an exception is raised the printing mechanism searches in the
global name-space to see if the exception has been declared there or in
a global structure. If it finds a matching identifier it uses the
type-information to print the arguments to the exception otherwise it
just prints the name.
Regards,
David
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