[llvm-dev] Re-numbering address space with a pass

Erdem Derebaşoğlu via llvm-dev
2015-11-02T13:50:17Z

My goal is to place thread-private variables in a different address space than
shared variables in an OpenMP program. I found out that lifetime.start
instrinsic starts the lifetime of shared objects before entering a parallel
region (in IR). So I am thinking about changing the address space of all
variables excluding those.
If I do it with a codegen pass, how can I look for lifetime_start/end operands
(since they are defined in IR level)? And when I do an addrspacecast, how do I
preserve the type?
Erdem.

Subject: Re: [llvm-dev] Re-numbering address space with a pass
From: arsenm2 at gmail.com
Date: Sun, 1 Nov 2015 13:14:22 -0800
CC: llvm-dev at lists.llvm.org
To: erdemderebasoglu at hotmail.com


On Nov 1, 2015, at 2:30 AM, Erdem Derebaşoğlu via llvm-dev <llvm-dev at
lists.llvm.org> wrote:Hi all,
I would like my optimization pass to change an object's address space that
is created by llvm.lifetime.start intrinsic. Because I want to be able to
identify them later in a codegen pass. I can get a pointer from the intrinsic
using CallInst::getArgOperand() function. However, I don't know what to do
with it (or if it is the pointer that I want). How can I change its address
space? If there is an easier way to "mark" that object, I would like
to know that too.
Thanks,Erdem._______________________________________________LLVM Developers
mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
There’s no easy way to change the address space of a value, though I would like
there to be one. You have to specifically handle all users and use mutateType.
AMDGPUPromoteAlloca is an example of a pass which does this, although it’s
somewhat buggy. If you’re just trying to identify the pointer with an address
space, you should be fine using an addrspacecast.
What are you trying to do with this? I don’t see why you would need special
handling just to identify these. In a codegen pass you can look at the
LIFETIME_START/LIFETIME_END operand which will give you the frame index which
you can identify users with.
-Matt
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