Add more safe points in compiler

runtime/vm/flow_graph.cc

Index: runtime/vm/flow_graph.cc
diff --git a/runtime/vm/flow_graph.cc b/runtime/vm/flow_graph.cc
index c14c18e5e792fec7e25013d395e9060d5b07aab3..b69c1af20e988099bcf50abba769cdc2743586bf 100644
--- a/runtime/vm/flow_graph.cc
+++ b/runtime/vm/flow_graph.cc
@@ -1316,6 +1316,7 @@ void FlowGraph::RemoveRedefinitions() {
   // Remove redefinition instructions inserted to inhibit hoisting.
   for (BlockIterator block_it = reverse_postorder_iterator(); !block_it.Done();
        block_it.Advance()) {
+    thread()->CheckForSafepoint();

[Vyacheslav Egorov (Google), 2017/03/27 14:11:51]

It seems strange to have a safepoint-per-block only here even though there are
more optimizations that iterate graph block by block.

[erikcorry, 2017/03/30 14:10:19]

I just picked the ones that showed up as slow for now.  With the new
--verbose-gc format we can keep an eye on it better.

     for (ForwardInstructionIterator instr_it(block_it.Current());
          !instr_it.Done(); instr_it.Advance()) {
       RedefinitionInstr* redefinition = instr_it.Current()->AsRedefinition();