Re: Stack based machines

plakal@cs.wisc.edu wrote:
> Linus Thand <thand@pmail.net> wrote:
> > What is happening in the world of stack-based machines?
> > Are there any active groups working on processors or compilers


And our wise moderator added:
> > [Registers give an architecture
> > a big performance boost, and it's hard to fake that by caching to top of
> > the stack. -John]


It is interesting that the x86 math coprocessors have been making
their stack-like registers architecture more and more un orthodox
since the Pentium. Stack operations now work by simple renaming of
registers, and the same goes for the FXCH instruction (which swaps the
stack top with another element).


In particular, FXCH (almost) always pairs with other instructions, and
allows one to (almost) emulate a register based architecture. In
particular, A*B+C*D+E*F can be rewritten to pipeline the three
multiplications so they run in parallel and are joined at the end.
Not exactly a conventional stack-based architecture...


Paolo Bonzini
[I think most people now agree that making the x86 FPU use a stack was
a mistake. Dunno why they did in the first place, I can't see any
particular advantage to it even on the 8087. -John]

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