tree 4997ddb7ef38e113accf9f99756af3eddbbd3699
parent a75624806550b804b5fe6c342716d64451e7f6ec
author Vyacheslav Egorov <vegorov@google.com> 1527012314 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1527012314 +0000

[vm/compiler] Do not use Constant(#null) to reserve space on the expression stack.

Given IL like this:

  t3 <- Constant(#null)   <--\
  // ... do something ...    |
  StoreLocal(:temp, t4)   ---/
  // Do something else
  StoreIndexed(t1, t2, t3)

Graph builder would use Constant(#null) as an input definition for
StoreIndexed - which leads to wrong generated code in unoptimized mode
on X64 where StoreIndexed has specialization for constant values. In
optimized code SSA renaming would actually replace t3 with a correct
reaching definition.

This CL introduces a new IL instruction MakeTemp(...) which has exactly
the same effect as Constant(#null) on the expression stack, but is
not treated as a constant value by the backend.

The bug was unnoticed because of the loose assertions in the SSA
renaming which permitted replacing Constant-s with non-Constant
reaching definitions. This CL also tightens those assertions to
catch this issue.

Also cleanup the code in SSA renaming a bit to make it a bit easier
to understand.

Fixes https://github.com/dart-lang/sdk/issues/33195

Bug: 33195
Change-Id: I7c914c836d4af7a50e8a8e1a02d03e9413f87779
Reviewed-on: https://dart-review.googlesource.com/56112
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>