Hi
As part of a requirement that I have, I would like to have some
globals reside in registers always. So these variables would not have
a home location in memory.
I realize the code generated would also need to be aware of this. I do
have some ideas on how to change the code appropriately. But right
now, I am more concerned about how to fit this requirement (sort of
interprocedural) into the existing LLVM register allocation framework.
While I can as part of pre regalloc pass allocate globals to
registers, how can I share this information between allocation of
different functions.
Allocation efficiency is not as much a concern and I am ok with doing
the allocation as a pre ra pass.
I will appreciate any pointers !
Shrey
Thanks Eli, Jaffrey for the pointer!
A couple of further questions if I may
1. Isnt this assuming that register being pinned to is always esi when
it comes to using a calling convention.
I would like to pin the register through a pass and so I dont know
which registers ends up being used for a particular value before hand
2. I would also like to allocate some small aggregates into registers.
I understand that the code generation would need to be non trivially
modified to do this.
I am wondering if it would be possible to create a map of this
information and using it in a modified existing allocator.
Modification would make sure the already allocated registers are not
available.
thanks again
shrey
Thanks Eli, Jaffrey for the pointer!
A couple of further questions if I may
1. Isnt this assuming that register being pinned to is always esi when
it comes to using a calling convention.
You'd need a separate calling convention for each possible set of
registers pinned. The combinatoric possibilities can get ugly, but
you probably only need a small fraction of the possibilities.
2. I would also like to allocate some small aggregates into registers.
I understand that the code generation would need to be non trivially
modified to do this.
You can always just split them in your pass... I don't know off the
top of my head whether returning a nested structure works at the
moment.
I am wondering if it would be possible to create a map of this
information and using it in a modified existing allocator.
Modification would make sure the already allocated registers are not
available.
You could, but it would be an ugly hack.
-Eli
Thanks Eli. At a implementation level, I am wondering if there is any
target specific class that I can use to store this information and use
it in the modified allocator later.
thanks
shrey