[llvm] r222142 - [Reassociate] As the expression tree is rewritten make sure the operands are

[suyog sarda]

Hi Chad, Timur

Just wanted to make a point here.

This patch actually eased further transformations like SLP Vectoization.

Test case :

sum = a[0] + a[1] + a[2] + a[3]

Earlier, without this patch, re-associate pass would re-organize this
expression into

sum = (((a[1] + a[0]) + a[2]) + a[3])

which made SLP vectorizer difficult to identify this type of horizontal
reduction.
With this patch, the expression would remain

sum = (((a[0] + a[1]) + a[2]) + a[3])

which made SLP vectorizer task simpler.

Patch holds good value for further optimization passes,
though as Timur reports that its breaking some test cases.

-- 
With regards,
Suyog Sarda
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