Re: Green Compiler ?

Hans-Peter Diettrich <DrDiettrich1@aol.com>
Sun, 30 Dec 2012 08:14:26 +0100

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From: Hans-Peter Diettrich <DrDiettrich1@aol.com>
Newsgroups: comp.compilers
Date: Sun, 30 Dec 2012 08:14:26 +0100
Organization: Compilers Central
References: 12-12-010 12-12-012 12-12-022 12-12-028 12-12-034
Keywords: code, performance

Peter Dassow schrieb:
> On 28.12.2012 08:35, Hans-Peter Diettrich wrote:
>>
>> Please note that most CMOS processor power consumption results from
>> switching (stray) capacities, and only a small percentage for leak
>> currents. E.g. a register or gate consumes such power whenever a bit is
>> changed, and almost nothing when it has reached an stable state.
>>
> So using extensively registers instead of "conventional" memory (e.g.
> DDR-RAM, memory outside a CPU) will save energy (if equal functionality
> is given) ?


I don't see a relationship here, except that external memory is slow
and [in x86] a couple of caches and address translations are involved
in reading from RAM. But registers are a very scarce resource, so that
frequent loading from memory is hardly avoidable. Register usage is
already optimized by every (good) compiler, reducing runtime and power
consuption at the same time. This was a very narrow bottleneck of the
IA-32 architecture, until the 64 bit (AMD) model increased the number
of registers considerably (16 addressable, of 128 [256?] shadow
registers). The CPU computation circuitry and usage is the same,
regardless of the operand sources.


DoDi


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