tree f0d5dfd15a80137ff699365105beb5f28fa4837d
parent 74410023acb796c460dabe6c05442ec32088e171
author John Stiles <johnstiles@google.com> 1636648612 -0500
committer SkCQ <skcq-be@skia-corp.google.com.iam.gserviceaccount.com> 1636657144 +0000

Improve index-folding of arrays and matrices.

Yesterday's implementation was close but I realized later that it wasn't
quite ideal.
- Array index-folding was gated on `isCompileTimeConstant`, which is too
  strict. The real limitation is `hasSideEffects`. If an array contains
  a side-effecting expression, we should leave it alone. Otherwise it
  is safe to pluck out an element from the array and toss the rest.
- Matrix index-folding was gated on `getConstantSubexpression` for the
  extracted elements, but did not check the other elements at all. This
  was too lenient; we now only proceed to the folding step if
  `hasSideEffects` returns false.

I added some tests to verify the final behavior and also discovered a
small related issue. Diagonal matrices were not substituting literals
in for constant-values, which inhibited folding as well and would break
constant-expression evaluation. This is now fixed.

Change-Id: Idda32fd8643c1f32ba21475251cd4d4dd7cea94c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/470396
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>