[Bug tree-optimization/26944] [4.1/4.2 Regression] -ftree-ch generates worse code

[Daniel Berlin]

> Compare pretmp.28_49 with pretmp.32_11, why are the arguments in a different
> order? Is there something unstable in the PRE algorithm?
> 

No, we just call fold on the expressions we build, and whatever it gives
us, we use :)