VM: Reduce the number of edge counters in generated code.

VM: Reduce the number of edge counters in generated code.

This CL avoids edge counters for the incoming edge of blocks that
 have one predecessor and one succesor block. The incoming count is
 always equal to the outgoing count (modulo exceptional exit by throwing).

R=johnmccutchan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=37170

[Cutch, 2014-06-06 14:56:12]

lgtm w/ minor comment

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language_mips.cc (right):

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
runtime/vm/intermediate_language_mips.cc:4503: (!last_instruction()->IsGoto() ||
Maybe add a comment here:

// Emit an edge counter when the block does not end in a GoTo or
// when this is not an exception catch block entry into the graph.
bool should_emit_edge_counter = !last_instruction()->IsGoto() ||
    (this == compiler->flow_graph().graph_entry()->normal_entry());

if (FLAG_emit_edge_counters && should_emit_edge_counter) {
...

[srdjan, 2014-06-06 14:59:51]

DBC

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language_ia32.cc (right):

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
runtime/vm/intermediate_language_ia32.cc:6004: (this ==
compiler->flow_graph().graph_entry()->normal_entry()))) {
How about factoring this test into TargetInstr::NeedsEdgeCounter().

[Florian Schneider, 2014-06-10 08:56:39]

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language_ia32.cc (right):

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
runtime/vm/intermediate_language_ia32.cc:6004: (this ==
compiler->flow_graph().graph_entry()->normal_entry()))) {
On 2014/06/06 14:59:51, srdjan wrote:
> How about factoring this test into TargetInstr::NeedsEdgeCounter().

Moved to FlowGraphCompiler::NeedEdgeCounter(TargetEntryInstr* block).

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
File runtime/vm/intermediate_language_mips.cc (right):

https://codereview.chromium.org/311993007/diff/60001/runtime/vm/intermediate_...
runtime/vm/intermediate_language_mips.cc:4503: (!last_instruction()->IsGoto() ||
On 2014/06/06 14:56:12, Cutch wrote:
> Maybe add a comment here:
> 
> // Emit an edge counter when the block does not end in a GoTo or
> // when this is not an exception catch block entry into the graph.
> bool should_emit_edge_counter = !last_instruction()->IsGoto() ||
>     (this == compiler->flow_graph().graph_entry()->normal_entry());
> 
> if (FLAG_emit_edge_counters && should_emit_edge_counter) {
> ...

Done.

[Florian Schneider, 2014-06-10 10:27:57]

Committed patchset #6 manually as r37170 (presubmit successful).