[llvm-dev] IPRA, interprocedural register allocation, question

[Lawrence, Peter via llvm-dev]

Vivek,
             I apologize if you took my original email as a request for implementation,
I meant to be asking what is already available, I think the answer to that
is the ‘preserves_most’ and ‘preserves_all’ attributes, but I will also
Use ‘regmask’ if those prove to be too sub-optimal.

I am still interested in figuring out the necessary and sufficient conditions
For LLC to do optimal IPRA when given a “whole program”
(as per my previous definition of “whole program”),
As opposed to how to accomplish this with LTO,

If you are open to having such discussions, even though your focus
IIUC is supposed to be LTO, then great.   I think Mehdi is stuck trying
To convince me to use LTO, but given all the changes I’ve had to make
To CodeGen (IE outside of my Target sub-dir) for having separate Data and Address
register sets, I think using LTO is a long term solution that I can’t take
On just now (IE the svn branch merge problem)

As one of my old math professors used to say “don’t use a sledge hammer
To crush a pea”,  to wit  I am only compiling a single source file as an entire whole
Program and I don’t do any linking, why should I have to use a linker.

--Peter Lawrence


Vivek,
          I have an application where many of the leaf functions are
Hand-coded assembly language,  because they use special IO instructions
That only the assembler knows about.  These functions typically don't
Use any registers besides the incoming argument registers, IE they don't
Need to use any additional callee-save nor caller-save registers.
Perhaps using some form of __attribute__ ?
Maybe __attribute__ ((registermask = ....))  ?


--Peter Lawrence.





From: vivek pandya [mailto:vivekvpandya at gmail.com]
Sent: Wednesday, July 13, 2016 11:47 AM
To: Lawrence, Peter <c_plawre at qca.qualcomm.com>
Cc: mehdi.amini at apple.com; llvm-dev <llvm-dev at lists.llvm.org>; llvm-dev-request at lists.llvm.org; Hal Finkel <hfinkel at anl.gov>
Subject: Re: [llvm-dev] IPRA, interprocedural register allocation, question

Hello Peter,

Are you still interested in __attribute__(regmask) ?
I have done some hack ( both clang+IPRA)  to get it working if you want to play around it I can send a patch by tomorrow.

Sincerely,
Vivek



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