VM: [Cleanup] Delete legacy code associated with BranchInstr.

VM: [Cleanup] Delete legacy code associated with BranchInstr.

1) BranchInstr::is_checked() was introduced back in the day when unoptimized
IR could contain comparisons like RelationalOp - these days unoptimized IR
can only contain StrictCompareInstr, other comparisons are represented as
calls and can't be merged into the branch, making BranchInstr::is_checked()
obsolete.

2) Constrained type support is no longer used: we deleted parts of the flow graph type propagator that propagated non-nullable types down from comparison with null (due to LICM issue).

R=fschneider@google.com

Committed: https://github.com/dart-lang/sdk/commit/67576af5f232b8b83e27f4b5c06872ed9c48c40c

[Vyacheslav Egorov (Google), 2017-01-18 20:31:41]

Description was changed from

==========
VM: [Cleanup] Delete legacy code associated with BranchInstr.

BranchInstr::is_checked() was introduced back in the day when unoptimized
IR could contain comparisons like RelationalOp - these days unoptimized IR
can only contain StrictCompareInstr, other comparisons are represented as
calls and can't be merged into the branch, making BranchInstr::is_checked()
obsolete.
==========

to

==========
VM: [Cleanup] Delete legacy code associated with BranchInstr.

1) BranchInstr::is_checked() was introduced back in the day when unoptimized
IR could contain comparisons like RelationalOp - these days unoptimized IR
can only contain StrictCompareInstr, other comparisons are represented as
calls and can't be merged into the branch, making BranchInstr::is_checked()
obsolete. 

2) Constrained type support is no longer used: we deleted parts of the flow
graph type propagator that propagated non-nullable types down from comparison
with null (due to LICM issue).
==========

[Vyacheslav Egorov (Google), 2017-01-18 20:31:41]

vegorov@google.com changed reviewers:
+ fschneider@google.com

[Vyacheslav Egorov (Google), 2017-01-18 20:31:51]

Hi Florian,

PTAL

[Florian Schneider, 2017-01-18 22:31:18]

Lgtm.

1. Good find and definitely not needed anymore.

2. I'd like to re-introduce propagating nullness (or non-nullness), but we need
to represent dependencies correctly (via Redefinitions), but I'm fine with
removing this dead code for now.

https://codereview.chromium.org/2640993003/diff/1/runtime/vm/flow_graph_build...
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/2640993003/diff/1/runtime/vm/flow_graph_build...
runtime/vm/flow_graph_builder.cc:1018:
RELEASE_ASSERT(definition->IsStrictCompare() || !definition->IsComparison());
ASSERT should be enough if you confirmed for all call sites of ReturnDefinition
that the only comparison is StrictCompare.

[Vyacheslav Egorov (Google), 2017-01-18 22:35:11]

2) Yeah I would like to reintroduce both not-null-ness and type refinement. We
either need dependencies - or we could reintroduce it post-LICM then
dependencies are not needed.

https://codereview.chromium.org/2640993003/diff/1/runtime/vm/flow_graph_build...
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/2640993003/diff/1/runtime/vm/flow_graph_build...
runtime/vm/flow_graph_builder.cc:1018:
RELEASE_ASSERT(definition->IsStrictCompare() || !definition->IsComparison());
On 2017/01/18 22:31:18, Florian Schneider wrote:
> ASSERT should be enough if you confirmed for all call sites of
ReturnDefinition
> that the only comparison is StrictCompare.

Sorry this was left from some experimental runs

[Vyacheslav Egorov (Google), 2017-01-18 22:59:01]

Description was changed from

==========
VM: [Cleanup] Delete legacy code associated with BranchInstr.

1) BranchInstr::is_checked() was introduced back in the day when unoptimized
IR could contain comparisons like RelationalOp - these days unoptimized IR
can only contain StrictCompareInstr, other comparisons are represented as
calls and can't be merged into the branch, making BranchInstr::is_checked()
obsolete. 

2) Constrained type support is no longer used: we deleted parts of the flow
graph type propagator that propagated non-nullable types down from comparison
with null (due to LICM issue).
==========

to

==========
VM: [Cleanup] Delete legacy code associated with BranchInstr.

1) BranchInstr::is_checked() was introduced back in the day when unoptimized
IR could contain comparisons like RelationalOp - these days unoptimized IR
can only contain StrictCompareInstr, other comparisons are represented as
calls and can't be merged into the branch, making BranchInstr::is_checked()
obsolete.

2) Constrained type support is no longer used: we deleted parts of the flow
graph type propagator that propagated non-nullable types down from comparison
with null (due to LICM issue).

R=fschneider@google.com

Committed:
https://github.com/dart-lang/sdk/commit/67576af5f232b8b83e27f4b5c06872ed9c48c40c
==========

[Vyacheslav Egorov (Google), 2017-01-18 22:59:03]

Committed patchset #2 (id:20001) manually as
67576af5f232b8b83e27f4b5c06872ed9c48c40c (presubmit successful).