[LLVMdev] dynamic typing system

Alec Benzer alecbenzer at gmail.com
Mon Aug 16 13:26:24 PDT 2010

This isn't a strictly llvm-related problem, but I thought I'd ask anyway to
see if anyone can help.

I'm trying to write a dynamically typed language on top of llvm. My initial
idea was to have a general object type for all objects in my language. I
came up with:

{ i8, i8* }

the first element of the structure would hold the type of the object, and
the second is a pointer to the actual data.

Now, I'm not exactly sure how to get my data allocated somewhere in order to
be able to get a pointer to it. My initial thought was heap allocations,
though there doesn't seem to be any llvm instructions that perform heap
allocations, though I imagine you just use C's malloc and free? If you do
use those, however, is there a way of getting the byte-size of a type, to
know what to pass to malloc? There's also the issue of having to know when
to be able to free() the pointers.

The other option, I guess, would be stack allocations with alloca
instructions? I don't need to worry about the sizes of types or about
calling free, but now my objects can't live on past the scope of a function,
which may complicate things. For instance, if at my jiting repl (set up like
the Kaleidoscope tutorial, where top-level expressions are wrapped in
lambdas and then executed), I type in "5", the repl should spit 5 back to
me. If I use allocas here there isn't a problem. But if I define a global
variable and assign 5 to it, the data I alloca'd is going to be gone after
the anonymous function returns. This makes it seem like heap allocations
would be a better choice.

So basically, I'm sort of stuck not knowing the best way to implement this
(or which way will even be possible). I'd appreciate any input/guidance on
how to proceed.
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