Add a backward instruction iterator and use it in the liveness analysis.

Add a backward instruction iterator and use it in the liveness analysis.

This avoids the complication when collecting the initial live_in sets while iterating forward.

Also simplify the ForwardInstructionIterator class because we have Goto instructions now and
the last instruction of each block does not use the next-link to
indicate a fall-through anymore.
Committed: https://code.google.com/p/dart/source/detail?r=9875

[Florian Schneider, 2012-07-24 14:24:15]

The two classes ForwardInstructionIterator and BackwardInstructionIterator could
share some code (e.g. Current()) For now I left it as is since it is only few
lines. I don't want to add a direction_ member variable, so a template class
would be the only option that is as efficient as having separate classes.

[Kevin Millikin (Google), 2012-07-24 14:40:40]

LGTM.

[Vyacheslav Egorov (Google), 2012-07-24 14:43:57]

LGTM

[srdjan, 2012-07-24 15:49:30]

LGTM

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
File vm/flow_graph_allocator.cc (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
vm/flow_graph_allocator.cc:71: // Iterate backwards.
Add:, starting with the last instruction of block.

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
File vm/intermediate_language.h (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
vm/intermediate_language.h:1989: Instruction* Current() const { return current_;
}
s/Current/current/   (also for ForwardInstructionIterator)

[srdjan, 2012-07-24 17:41:44]

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
File vm/flow_graph_allocator.cc (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
vm/flow_graph_allocator.cc:77: if ((current_def != NULL) &&
(current_def->ssa_temp_index() >= 0)) {
current_def->HasSSATemp()

[Florian Schneider, 2012-07-25 08:31:29]

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
File vm/flow_graph_allocator.cc (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
vm/flow_graph_allocator.cc:71: // Iterate backwards.
On 2012/07/24 15:49:30, srdjan wrote:
> Add:, starting with the last instruction of block.

Done.

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/flow_graph_allocato...
vm/flow_graph_allocator.cc:77: if ((current_def != NULL) &&
(current_def->ssa_temp_index() >= 0)) {
On 2012/07/24 17:41:44, srdjan wrote:
> current_def->HasSSATemp()

Done.

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
File vm/intermediate_language.h (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
vm/intermediate_language.h:1989: Instruction* Current() const { return current_;
}
On 2012/07/24 15:49:30, srdjan wrote:
> s/Current/current/   (also for ForwardInstructionIterator)

I leave it as is to be consistent with the names of the other functions in the
iterator interface (either all lower- or all upper-case)

[srdjan, 2012-07-25 15:19:29]

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
File vm/intermediate_language.h (right):

https://chromiumcodereview.appspot.com/10796108/diff/1/vm/intermediate_langua...
vm/intermediate_language.h:1989: Instruction* Current() const { return current_;
}
On 2012/07/25 08:31:29, Florian Schneider wrote:
> On 2012/07/24 15:49:30, srdjan wrote:
> > s/Current/current/   (also for ForwardInstructionIterator)
> 
> I leave it as is to be consistent with the names of the other functions in the
> iterator interface (either all lower- or all upper-case)

Yes, the consistency argument is valid.
Since lower-casing is is used to denote calling short inlined functions, the
best will be to change Advance, Done, and Current  to lower case. See C++ style
guide:
http://www.corp.google.com/eng/doc/cppguide.xml?showone=Function_Names#Functi...