Currently, SkSL is able to constant-propagate `x = x + constant` into
`x = constant` when the starting value of x is known. However, it is not
able to do the same optimization for `x += constant`. This test
demonstrates that once += is encountered, we lose track of x's value and
can no longer propagate its value.
(This is equally true of all the op-assignment operators, += -=
*= /= etc.)
Change-Id: I3523e96baf9a73982cf3b09f0d23b95adacf106b
Bug: skia:11192
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368248
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
