Support allocation sinking for compound objects.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 60a66aba9969e7fa3b68b3671c19774e6d2a5275..557d61ce86758dd8d5caa7388953b656bdcfa90f 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -479,6 +479,10 @@ static bool CompileParsedFunctionHelper(ParsedFunction* parsed_function,
         DeadCodeElimination::EliminateDeadPhis(flow_graph);
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
 
+        if (optimizer.Canonicalize()) {
+          optimizer.Canonicalize();

[srdjan, 2014/07/17 23:08:14]

Why another canonicalization?

[Vyacheslav Egorov (Google), 2014/07/18 11:25:08]

When writing tests I noticed that we often arrive to the following IR right
before allocation sinking:

v1 <- AllocateObject(...)
...
CheckClass(v1, ...)

I run one more canonicalization to remove this CheckClass instruction.

Ideally our Canonicalize just needs to run every time we rewire uses, otherwise
we constantly miss optimization opportunities.

+        }
+
         // Attempt to sink allocations of temporary non-escaping objects to
         // the deoptimization path.
         AllocationSinking* sinking = NULL;