[PATCH] Add support for symbolic large constant entries inside stackmaps

[Marius Wachtler]

Hi,
The attached patch implements support for embedding symbols in the array of
large constants inside a stackmap/patchpoint.
We (=Pyston project) embed in the LLVM IR we generate a lot of pointers to
external constants. I would like to cache the JITed functions and therefore
I need to make the embedded constants relocatable -> change the IR to refer
to module variables instead which I can replace when loading the cached
object.
Currently when a patchpoint has a constant variable as live argument it
will materialize it in a register. Which we don't want because the live
variables are rarely used (also the regalloc runs out of registers when
having to many const variables as argument to the pp?!?...).
This patch emits a symbol reference inside the array of large constants in
the stackmap. The stack map format is untouched by this patch.

Together with
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150330/269160.html
this should make it possible to cache more JITed functions containing
patchpoints.

Looking forward to comments on this patch.
Cheers,
Marius
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