Re: Selective Computation...

Patrick Volteau <Patrick.Volteau@st.com>
20 Jan 2003 23:55:27 -0500

          From comp.compilers
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Selective Computation... saru@jeyan.eclipse.co.uk (Saru) (2002-12-26)
Re: Selective Computation... jeyan@jeyan.eclipse.co.uk (Saru) (2002-12-30)
Re: Selective Computation... saru@jeyan.eclipse.co.uk (Saru) (2002-12-30)
Re: Selective Computation... joachim_d@gmx.de (Joachim Durchholz) (2002-12-31)
Re: Selective Computation... thp@cs.ucr.edu (2003-01-17)
Re: Selective Computation... Patrick.Volteau@st.com (Patrick Volteau) (2003-01-20)
Re: Selective Computation... strohm@airmail.net (John R. Strohm) (2003-01-21)
Re: Selective Computation... andreas.gieriet@externsoft.ch (Andreas Gieriet) (2003-01-21)
Re: Selective Computation... liekweg@freenet.de (Florian Liekweg) (2003-01-21)
Re: Selective Computation... marcov@toad.stack.nl (Marco van de Voort) (2003-02-06)
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From: Patrick Volteau <Patrick.Volteau@st.com>
Newsgroups: comp.compilers
Date: 20 Jan 2003 23:55:27 -0500
Organization: STMicroelectronics
References: 02-12-116 03-01-077
Keywords: performance, comment
Posted-Date: 20 Jan 2003 23:55:27 EST

> [On modern architectures, conditional branches can be slow. -John]


Yes but now some architecture provide predicated instructions where an
instruction is executed conditionally.


For example for the expression proposed here, one could use:
(k1, k2, k3, p, q, p', q and X are symbolique names for registers
  p0, p1, p2 are predicates (true or false)
  I'm using an algebraic assembly syntax)


                p0 = (k1 == 1)
                p1 = (k2 == 1)
                p2 = (k3 == 1)
      p0 ? X = p + q
      p1 ? X = p + q'
      p2 ? X = p' + q


Nice, isn't it?


Patrick.
[Not new, either. I programmed a Varian mini in about 1969 that had
conditional execute instructions that we used for similar
things. -John]

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