tree 1ebef46a3e6bf93464530abc09c5267fd095e66e
parent e67dd9c2c5e7c88985b14b43c54b1b30d2af7918
author Alexander Markov <alexmarkov@google.com> 1618437071 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1618437071 +0000

[vm/compiler] Canonicalize v1 = Phi(v2, v1)

Previously, compiler canonicalized Phi instructions which reference
only one value (modulo redefinitions):

   v1 = Phi(v2, v2, ..., v2)

This change extends the canonicalization rule to also allow the Phi
to reference itself:

  v1 = Phi(v2, v2, ...., v2, v1, ...., v1)

Such Phi instructions may occur in loops when local variable is not
mutated (remains the same on the back-edge).

TEST=ci
Change-Id: I2838c4307a6dd3067d52624db66487ba4682538c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/195043
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>