5 Jan 2001 14:04:55 -0500

Related articles |
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non trivial constant folding mpointie@eden-studios.fr (Mickaël Pointier) (2001-01-05) |

Re: non trivial constant folding broeker@physik.rwth-aachen.de (Hans-Bernhard Broeker) (2001-01-05) |

Re: non trivial constant folding mihai@cs.wisc.edu (Mihai Christodorescu) (2001-01-06) |

Re: non trivial constant folding pat@jantar.org (Patryk Zadarnowski) (2001-01-06) |

Re: non trivial constant folding bonzini@gnu.org (2001-01-06) |

Re: non trivial constant folding idbaxter@semdesigns.com (Ira D. Baxter) (2001-01-06) |

Re: non trivial constant folding cfc@world.std.com (Chris F Clark) (2001-01-06) |

[16 later articles] |

From: | "Mickaël Pointier" <mpointie@eden-studios.fr> |

Newsgroups: | comp.compilers |

Date: | 5 Jan 2001 14:04:55 -0500 |

Organization: | ImagiNET / Colt Internet |

Keywords: | optimize, question, comment |

Posted-Date: | 05 Jan 2001 14:04:54 EST |

Hi.

I've been searching on the web for information about this

particular problem, as well as in my books ("Compiler

Construction" - Niklaus Wirth, and "Crafting a Compiler

with C" - Fisher/LeBlanc) but does not find anything

clear about it.

I'm parsing expression to create a tree made of nodes

that contains either "operators" or "values". This works

fine, so I've started to "optimise" the resulting tree with

a code that recursively compute all the operators that

have immediate childs that are two immediate numerical

values.

This works fine for an expression like this:

eval(1+2+3/2+4+5*8)

is translated in this tree:

+(+(+(+(1.000000,2.000000),/(3.000000,2.000000)),4.000000),*(5.000000,8.0000

00))

And optimised like this:

Optimise + (1.000000+2.000000=3.000000)

Optimise / (3.000000/2.000000=1.500000)

Optimise + (3.000000+1.500000=4.500000)

Optimise + (4.500000+4.000000=8.500000)

Optimise * (5.000000*8.000000=40.000000)

Optimise + (8.500000+40.000000=48.500000)

Giving this final evaluate expression:

48.500000

My problem is that I do not manage to find a clean solution

to optimise this:

eval(1+var+1)

is translated as:

+(+(1.000000,var),1.000000)

And I do not manage to optimise it.

(Of course eval(1+1+var) is optimised in "+(2.000000,var)")

I've been looking extensively on how I can reorganise my

expression tree, but do not manage to find any explanation.

I believe it's a question that's often ask (I found a question

on this subject by "Tim Pierce" in 1992 in this newsgroup,

but do not find the answer...)

Thanks in advance for any help

Mickael Pointier

PS: Happy new year

[I've seen compilers that do that. With associative operators like +

they combine all of the operands of a set of cascaded operators into

a list or array, then sort that array to get the constants together.

-John]

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