Fix convergence issues in range analysis.

Fix convergence issues in range analysis.

Split it into three phases: initialization, widening and narrowing.

During widening and narrowing phi-ranges change according to classical widening and narrowing operators defined as:

Widening:
  [_|_, _|_] v [a, b] = [a, b]
  [a, b] v [c, d] = [c < a ? -inf : a, d > b ? +inf : b]

Narrowing:
  [a, b] ^ [c, d] = [(a == -inf) ? c : min(a, c), (b == +inf) ? d : max(b, d)]

R=fschneider@google.com

Committed: https://code.google.com/p/dart/source/detail?r=12772

[Florian Schneider, 2012-09-24 11:29:59]

lgtm

https://codereview.chromium.org/10972003/diff/1/runtime/vm/flow_graph_optimiz...
File runtime/vm/flow_graph_optimizer.cc (right):

https://codereview.chromium.org/10972003/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:1547: for (intptr_t i = 0; i <
join->phis()->length(); ++i) {
Use PhiIterator here?

https://codereview.chromium.org/10972003/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:1575: flow_graph_->current_ssa_temp_index());
Does it fit into the previous line?

https://codereview.chromium.org/10972003/diff/1/runtime/vm/flow_graph_optimiz...
runtime/vm/flow_graph_optimizer.cc:1657: for (intptr_t i = 0; i <
smi_values_.length(); i++) {
I assume that you only add phis here because only phis can change their range in
the widening pass. Please add a comment.

[Vyacheslav Egorov (Google), 2012-09-24 12:00:05]

comments addressed. landing.