[llvm-dev] virtual registers

[John Criswell via llvm-dev]

On 2/18/16 1:17 PM, Laura personen wrote:
> Thank you for your swift reply.
>
> I also need some reference about instruction sequence in llvm. I mean, 
> do the order of instructions remain the same as they appear in a .ll 
> file? or do they change by different optimizations (e.g. SSA-based 
> Machine Code Optimizations 
> <http://llvm.org/docs/CodeGenerator.html#ssa-based-machine-code-optimizations>, 
> Late Machine Code Optimizations 
> <http://llvm.org/docs/CodeGenerator.html#late-machine-code-optimizations>, 
> etc.)?

I believe there are optimizations that can change the order of 
instructions at the LLVM IR level.  You can find a list of LLVM 
optimizations at http://llvm.org/docs/Passes.html.

When generating native code, the Instruction Scheduler will reorder the 
native code instructions as well.

>
> If they change, which algorithms are used for reordering instructions? 
> I appreciate a reference that explains them or just gives the name of 
> the algorithms that are used.

You can look at the list of passes, but to get more detail, you will 
probably need to examine the source code.

Regards,

John Criswell

>
> BR
> Laura
>
> On Thu, Feb 18, 2016 at 6:45 PM, John Criswell <jtcriswel at gmail.com 
> <mailto:jtcriswel at gmail.com>> wrote:
>
>     On 2/18/16 12:03 PM, Laura personen via llvm-dev wrote:
>>     Hi,
>>
>>     Is there any way to detect which virtual registers are assigned
>>     to physical registers and which ones are assigned to memory slots?
>
>     At the LLVM IR level, no.  However, it might be possible for a
>     MachineFunctionPass to determine this or to modify the register
>     allocator to record this information somewhere for query by a
>     MachineFunctionPass later.
>
>     Regards,
>
>     John Criswell
>
>
>>
>>     BR
>>     Laura
>>
>>
>>     _______________________________________________
>>     LLVM Developers mailing list
>>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>>     http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>     -- 
>     John Criswell
>     Assistant Professor
>     Department of Computer Science, University of Rochester
>     http://www.cs.rochester.edu/u/criswell
>
>


-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160218/df5bbd85/attachment.html>