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From: Jan-Jaap van der Heijden
Subject: Bug fixes (was: "Recursion, need more stack space.")
Date: 17 Jun 1997, 00:43:29

On Sun, 5 May 2097, PredatorZeta wrote:

> Peter Gerwinski <peter@agnes.dida.physik.uni-essen.de> wrote:
> 
> > Or else: Loading the memory reference into a register and
> > pushing that *might* be faster than a direct push (don't know).
> 
> Just little clarifying.....:))
> No. Surely not on 80x86 machines. Look this (is for Pentium):
> 
> 1      push (mem)            take 2 cycles NOT pairable 
> 
> 2   a) mov (mem), reg     take 1 cycle pairable 
>                                      AGI Stall (1 cycle+cut off pairing
> system)
>      b) push reg               take 1 cycle pairable
> 
>       TOTAL:                    3 cycles
> 
> Well, is 2 (not pairable) versus 2 1/2 (not pairable) cycles.....
> However, with a manual re-ordering it could take only 1 cycle...8-))
> 

The GCC 2.7.2.x backend used by GPC knows nothing about pentium
optimzations or instruction scheduling. However, I happen to have a
Cygnus-CDK based GPC around that _does_ know pentium optimizations and it
still produces the same assembly. So, I guess more work is needed here
(by the GCC crew), although this compiler produces significantly faster
code already :-)

JanJaap

---
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going
to land, and it could be dangerous sitting under them as they fly
overhead.  -- RFC1925.

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