transformations: (canonicalize) Arith const reassociation

[n-io]

This adds the second of two canonicalisation patterns for FloatingPointLikeBinaryOperations on arith.constants.

• Ops with two constant operands are folded by canonicalisation, regardless of math flags (see transformations: Canonicalizations for arith on float constants #3362 )
• Chained ops of the form (const1 * var) * const2 are rewritten as (const1 * const2) * var iff the fastmath<reassoc> or fastmath<fast> flags are set, and if the ops are multiplications or additions. Note, this is not currently implemented in upstream mlir.

See here to check how it works in upstream mlir.

Note, these canonicalisations currently do not support container types.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.10%. Comparing base (a5628c9) to head (5bd9c00).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3364   +/-   ##
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  Coverage   90.10%   90.10%           
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  Files         449      449           
  Lines       56666    56686   +20     
  Branches     5440     5443    +3     
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+ Hits        51060    51079   +19     
  Misses       4168     4168           
- Partials     1438     1439    +1     

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[math-fehr]

Nice! I just had a qustion about the flags to add in the new created operation, but otherwise everything is good! Thanks!

[math-fehr]

Is the resulting flag the or of both operations?
I am out of my depth here, is it what MLIR does?

[n-io]

Yes, since we're essentially folding two ops into one, I wasn't entirely sure how to set the flags on the new op. The union set of both ops seemed like a cleaner option as compared to picking either one at random. I am not entirely sure myself as to how mlir would resolve such a case.

[alexarice]

I would also prefer to see the checks appear above the tests here, but feel free to ignore