Try allocating loop phi into a register even if phi has only unconstrained uses but there are cheap…

Try allocating loop phi into a register even if phi has only unconstrained uses but there are cheap eviction candidates: values that come into the loop and have only unconstrained uses in it.

When spilling a value inside the loop that has only unconstrained uses in this loop move spilling point outside of the loop.

This tweaks allow to minimize amount of memory moves on loop back edges.

R=fschneider@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=14673

[Florian Schneider, 2012-11-08 02:05:36]

lgtm

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:724: const intptr_t is_loop_header =
join->loop_info() != NULL;
Move this down to the use.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1525: from));
Please make sure that this code is covered in our tests.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1703: } else {
} else if (interval->start() < loop_end) {

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1721: for (int reg = 0; reg <
NumberOfRegisters(); ++reg) {
intptr_t?

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1733: // If a loop phi has no register uses
we might still want to allocate it
Please split this 4-line sentence into simpler phrases.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1736: // cheaply evicated i.e. it has no
register beneficial uses inside the
s/evicated/evicted/g

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1741: !(unallocated->is_loop_phi() &&
HasCheapEvictionCandidate(unallocated))) {
Please make sure that this part is hit in our tests.

[Vyacheslav Egorov (Google), 2012-11-08 02:13:43]

Thank you for the review.

Landing.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:724: const intptr_t is_loop_header =
join->loop_info() != NULL;
On 2012/11/08 02:05:36, Florian Schneider wrote:
> Move this down to the use.

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1525: from));
On 2012/11/08 02:05:36, Florian Schneider wrote:
> Please make sure that this code is covered in our tests.

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1703: } else {
On 2012/11/08 02:05:36, Florian Schneider wrote:
> } else if (interval->start() < loop_end) {

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1721: for (int reg = 0; reg <
NumberOfRegisters(); ++reg) {
On 2012/11/08 02:05:36, Florian Schneider wrote:
> intptr_t?

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1733: // If a loop phi has no register uses
we might still want to allocate it
On 2012/11/08 02:05:36, Florian Schneider wrote:
> Please split this 4-line sentence into simpler phrases.

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1736: // cheaply evicated i.e. it has no
register beneficial uses inside the
On 2012/11/08 02:05:36, Florian Schneider wrote:
> s/evicated/evicted/g

Done.

https://codereview.chromium.org/11361161/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1741: !(unallocated->is_loop_phi() &&
HasCheapEvictionCandidate(unallocated))) {
On 2012/11/08 02:05:36, Florian Schneider wrote:
> Please make sure that this part is hit in our tests.

Done.