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>
6ee5d9e3c9