Heuristically predict interference on the back edge and use it to minimize number of register reshu…

Heuristically predict interference on the back edge and use it to minimize number of register reshuffling which is especially expensive when cycles of XMM registers arise.

When allocating free register check if hint can potentially interfere on the back edge try ignoring hint and search for a better candidate.

Additionally fix handling of constants in the liveness analysis to accommodate constants used as immediates.

R=fschneider@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=15291

[Florian Schneider, 2012-11-23 13:58:05]

LGTM.

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1690: Definition* input =
phi->InputAt(i)->definition();
Or shorter:

input_phi = phi->InputAt(i)->definition()->AsPhi();
if (input_phi != NULL) { ...

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1743: // If we are in the loop try to reduce
number of moves on the back edge by
Which loop? s/the/a/?

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1751:
ASSERT(static_cast<intptr_t>(kNumberOfXmmRegisters) <=
COMPILE_ASSERT?

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1765: if ((unallocated->vreg() >= 0) &&
This condition is already tested in line 1747.

[Vyacheslav Egorov (Google), 2012-11-23 15:38:53]

Thanks for the review. Landing.

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
File runtime/vm/flow_graph_allocator.cc (right):

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1690: Definition* input =
phi->InputAt(i)->definition();
On 2012/11/23 13:58:06, Florian Schneider wrote:
> Or shorter:
> 
> input_phi = phi->InputAt(i)->definition()->AsPhi();
> if (input_phi != NULL) { ...

Done.

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1743: // If we are in the loop try to reduce
number of moves on the back edge by
On 2012/11/23 13:58:06, Florian Schneider wrote:
> Which loop? s/the/a/?

Done.

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1751:
ASSERT(static_cast<intptr_t>(kNumberOfXmmRegisters) <=
On 2012/11/23 13:58:06, Florian Schneider wrote:
> COMPILE_ASSERT?

COMPILE_ASSERT seems to be available only in debug.

https://codereview.chromium.org/11418135/diff/1/runtime/vm/flow_graph_allocat...
runtime/vm/flow_graph_allocator.cc:1765: if ((unallocated->vreg() >= 0) &&
On 2012/11/23 13:58:06, Florian Schneider wrote:
> This condition is already tested in line 1747.

Done.