tree 65373da50fef156fbe231301281b84f09ef15a1e
parent 04e329b6ede7954a40d8121347a55bb385a1139a
author Alexander Markov <alexmarkov@google.com> 1558373894 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1558373894 +0000

[vm/compiler] Avoid adding unused Redefinition instructions

Type propagator adds Redefinition instructions to provide more accurate
type information only for dominated uses (for example, to mark receiver
as non-nullable after instance calls). However, adding Redefinition
instructions may interfere with branch simplification, which looks only
at empty join blocks. This change avoids adding unused Redefinition
instructions (if there are no dominated uses).

This particular situation happens in Flutter in RenderObject.layout() where
constraints.isTight is inlined with multiple polymorphic targets, including
SliverConstraints.isTight which returns false.
Branch simplification was not happening due to Redefinition instruction
for 'constraints'. That Redefinition instruction is not used.

Change-Id: I15082bacd7cc6ea1445a4dadc8ef97853142ba74
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103023
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>