hpcc-systems/HPCC-Platform — pull request #2898 by ghalliday (2012-07-20 16:14:50+00:00)
Title: Resolve problems with ambiguous LEFT

Addresses issue #2864. This fixes examples ambigleft.ecl and grouproll6.ecl are fixed by these changes.

This branch is very close to being ready to pull. There are a few known issues:

* Memory consumption is much higher. There are other branches trying to address that.

Some examples from internal .
jholt20 - unique selectors are generated before global constant folding, which means that some expressions that would become identical are treated as different.

qrec - a two projects are pushed down the graph (over if branches), and would become common if they had the same sequence.

saltstep - converting exists(topn) to exists(choosen) could be more efficient, but leads to an extra activity.

jwindle1 project doesn't get moved down the tree.