Fix bug in load elimination with multiple phis.

Fix bug in load elimination with multiple phis.

The in-set has to be computed on the out-sets of the predecessors with
the phi-moves of the predecessor applied. This is now done on a temporary
copy of out, instead of the out-set itself - otherwise the phi-moves may
 be applied more than once to the same set.

BUG=http://dartbug.com/17159
TEST=tests/language/vm/load_to_load_forwarding_vm_test.dart
R=vegorov@chromium.org

Committed: https://code.google.com/p/dart/source/detail?r=33118

[Vyacheslav Egorov (Chromium), 2014-02-27 16:25:08]

lgtm

https://codereview.chromium.org/183303002/diff/1/runtime/vm/flow_graph_optimi...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/183303002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:5994: if (pred_out != NULL) {
I would write it slightly differently:

if (pred_out == NULL) continue;

PhiPlaceMoves::MovesList phi_moves =
aliased_set_->phi_moves()->GetOutgoingMoves(pred);
if (phi_moves != NULL) {
  // If there are phi moves, perform intersection with
  // a copy of pred_out where the phi moves are applied.
  temp_out->CopyFrom(pred_out);
  PerformPhiMoves(phi_moves, temp_out, forwarded_loads);
  pred_out = temp_out;
}

temp->Intersect(pred_out);

[Florian Schneider, 2014-02-27 16:32:14]

Committed patchset #2 manually as r33118 (presubmit successful).

[Florian Schneider, 2014-02-28 13:38:57]

https://codereview.chromium.org/183303002/diff/1/runtime/vm/flow_graph_optimi...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/183303002/diff/1/runtime/vm/flow_graph_optimi...
runtime/vm/flow_graph_optimizer.cc:5994: if (pred_out != NULL) {
On 2014/02/27 16:25:09, Vyacheslav Egorov wrote:
> I would write it slightly differently:
> 
> if (pred_out == NULL) continue;
> 
> PhiPlaceMoves::MovesList phi_moves =
> aliased_set_->phi_moves()->GetOutgoingMoves(pred);
> if (phi_moves != NULL) {
>   // If there are phi moves, perform intersection with
>   // a copy of pred_out where the phi moves are applied.
>   temp_out->CopyFrom(pred_out);
>   PerformPhiMoves(phi_moves, temp_out, forwarded_loads);
>   pred_out = temp_out;
> }
> 
> temp->Intersect(pred_out);

Done.