[llvm-commits] patch: chrec * chrec = chrec.

[Nick Lewycky]

This patch is a follow-up to r139133 which corrected SCEV's getMulExpr 
when given two chrec arguments. Here I extend it to correctly multiply 
chrecs of any length.

The meat of this patch is a pure blob of illegible math. If you want to 
do a hard review, I would suggest:
  - trying to derive the formula I used in the comment to calculate the 
terms of the new chrec
  - proving to yourself a coefficient that doesn't fit can safely be 
truncated

If you want to do an easier review, I would suggest running it over 
code. This will fire in 447.dealII for example.

I know that other work is going on in the loop optimizer right now which 
I don't want to interfere with, so please let me know when wouldn't be a 
bad time to land this.

Nick
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