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Re: register at file scope

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Am 29.10.19 um 10:00 schrieb Philipp Klaus Krause:
> Introducing this as a compiler extension first and also evaluate the
> impact of placing register in appropriate places in some real-world code
> or a benchmark would indeed make sense.
> 
> Philipp
> 

I did a first experiment; there, the improvements in benchmarks are far
less than what one sees in synthetic examples.

Experiment:

* SDCC version based on current SDCC with support for register at file
scope added. For now, the information is used in two places in
redundancy elimination only.
* Annotated file scope variables in 4 benchmarks (Coremark, Dhrystone,
stdcbench, Whetstone) with register storage class where appropriate.
* Compiled the benchmarks for STM8 with strong optimization
(--max-allocs-per-node 100000), using default balanced optimization goal.

Results:

* stdcbench, Coremark: No difference at all. No surprise, since they
both use very few file scope variables, and typically not in the inner
loops.
* Whetstone: 0.8 % increase in score, 0.3 % reduction in code size.
Whtstone uses some file scope variables, but doesn't do much with
pointers, so no surprise here, either.
* Dhrystone: 1.4 % increase in score, 0.1 % increase in code size. IMO,
1.4 % is a surprisingly large increase, considering that Dhrystone tends
to spent most of its time in string functions from the standard library,
which are not affected by the change at all.

Philipp

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Thread

register at file scope Philipp Klaus Krause <pkk@spth.de> - 2019-10-25 12:45 +0200
  Re: register at file scope David Brown <david.brown@hesbynett.no> - 2019-10-26 17:33 +0200
    Re: register at file scope Philipp Klaus Krause <pkk@spth.de> - 2019-10-26 19:24 +0200
      Re: register at file scope David Brown <david.brown@hesbynett.no> - 2019-10-27 12:39 +0100
        Re: register at file scope Philipp Klaus Krause <pkk@spth.de> - 2019-10-28 12:22 +0100
          Re: register at file scope David Brown <david.brown@hesbynett.no> - 2019-10-28 15:28 +0100
            Re: register at file scope Philipp Klaus Krause <pkk@spth.de> - 2019-10-29 10:00 +0100
              Re: register at file scope David Brown <david.brown@hesbynett.no> - 2019-10-29 13:46 +0100
              Re: register at file scope Philipp Klaus Krause <pkk@spth.de> - 2019-11-25 12:19 +0100

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