Talk:Common subexpression elimination
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Hello!
I think that there is an error in example. Here is my suggestion how it should be: _______________________
Here is a simple example:
a = b * c + g; c = b * c * d; e = b * c;
which does four multiplies and one addition, can be replaced by
tmp = b * c; a = tmp + g; c = tmp * d; e = b * c;
which does three multiplies and one add.
Variable "e" can't be replaced with "tmp", because in third line value of "c" is changed - so value of "tmp" is not correct anymore (out-of-date). We have to recalculate value of "tmp" or let this (4th) line well alone (no substitution).
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English is not my native language, so I didn't correct the page, beacause of possible language mistakes...
PS: Maybe I'm wrong about this error?
Mirek [PL]
- Ooops! I'll fix it. Stan 22:12, 22 May 2004 (UTC)