Remove the LoadLocal used at the end of a temp local scope.

Remove the LoadLocal used at the end of a temp local scope.

The previous pattern was:

1. FP-relative load of the top of the stack
2. Push #1
3. Pop
4. Pop
5. Push #3

Where #5 was omitted when the value was unused.

The new pattern is:

1. Pop
2. Push #1

Where #2 is omitted when the value is unused.

R=fschneider@google.com

Committed: https://github.com/dart-lang/sdk/commit/f26e70ad3e420decbe3e783624f415fe69af9361

[Kevin Millikin (Google), 2016-05-10 08:19:46]

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

[Kevin Millikin (Google), 2016-05-10 08:19:47]

https://codereview.chromium.org/1963683003/diff/1/runtime/vm/flow_graph_build...
File runtime/vm/flow_graph_builder.cc (right):

https://codereview.chromium.org/1963683003/diff/1/runtime/vm/flow_graph_build...
runtime/vm/flow_graph_builder.cc:2260: return new(Z) DropTempsInstr(0, value);
We can eliminate this Drop instruction if the value is needed and just use the
value instead which will consume it from the stack.

That change requires plumbing a flag through a few levels of helper functions
and changing the responsibility of emitting the possible Drop instruction from
the callers to this function.  I didn't make that change here.

[Florian Schneider, 2016-05-10 08:27:05]

Lgtm!

[Florian Schneider, 2016-05-19 10:32:45]

Should I land this for you?

[Kevin Millikin (Google), 2016-05-20 10:40:14]

Description was changed from

==========
Remove the LoadLocal used at the end of a temp local scope.

The previous pattern was:

1. FP-relative load of the top of the stack
2. Push #1
3. Pop
4. Pop
5. Push #3

Where #5 was omitted when the value was unused.

The new pattern is:

1. Pop
2. Push #1

Where #2 is omitted when the value is unused.
==========

to

==========
Remove the LoadLocal used at the end of a temp local scope.

The previous pattern was:

1. FP-relative load of the top of the stack
2. Push #1
3. Pop
4. Pop
5. Push #3

Where #5 was omitted when the value was unused.

The new pattern is:

1. Pop
2. Push #1

Where #2 is omitted when the value is unused.

R=fschneider@google.com

Committed:
https://github.com/dart-lang/sdk/commit/f26e70ad3e420decbe3e783624f415fe69af9361
==========

[Kevin Millikin (Google), 2016-05-20 10:40:16]

Committed patchset #1 (id:1) manually as
f26e70ad3e420decbe3e783624f415fe69af9361 (presubmit successful).