Add deoptimization history to optimized functions.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 23072)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -3415,8 +3415,6 @@
 void LICM::Hoist(ForwardInstructionIterator* it,
                  BlockEntryInstr* pre_header,
                  Instruction* current) {
-  // TODO(fschneider): Avoid repeated deoptimization when
-  // speculatively hoisting checks.
   if (FLAG_trace_optimization) {
     OS::Print("Hoisting instruction %s:%"Pd" from B%"Pd" to B%"Pd"\n",
               current->DebugName(),
@@ -3472,7 +3470,7 @@
   }
 
   // Host CheckSmi instruction and make this phi smi one.
-  Hoist(it, pre_header, current);
+  if (MayHoist(current, pre_header)) Hoist(it, pre_header, current);
 
   // Replace value we are checking with phi's input.
   current->value()->BindTo(phi->InputAt(non_smi_input)->definition());
@@ -3491,6 +3489,31 @@
 }
 
 
+bool LICM::MayHoist(Instruction* instr, BlockEntryInstr* pre_header) {
+  // TODO(fschneider): Enable hoisting of Assert-instructions
+  // if it safe to do.
+  if (instr->IsAssertAssignable()) return false;
+  if (instr->IsAssertBoolean()) return false;
+
+  if (instr->CanDeoptimize()) {
+    intptr_t target_deopt_id =
+        pre_header->last_instruction()->AsGoto()->GetDeoptId();
+    const Function& function = flow_graph_->parsed_function().function();
+    const Array& deopt_history = Array::Handle(function.deopt_history());
+    if (deopt_history.IsNull()) return true;
+
+    for (intptr_t i = 0; i < deopt_history.Length(); ++i) {
+      const Object& obj = Object::Handle(deopt_history.At(i));
+      if (obj.IsNull()) continue;

[Kevin Millikin (Google), 2013/05/24 11:39:21]

If you just delete this line, I think the result is exactly the same.

[Florian Schneider, 2013/05/24 11:53:02]

Done.

+      if (obj.IsSmi() && Smi::Cast(obj).Value() == target_deopt_id) {

[Kevin Millikin (Google), 2013/05/24 11:39:21]

Can it be non-smi (other than null)?  The Smi::Cast will assert it is.  If it's
always smi or null you can just use:

Smi& deopt_id = Smi::Handle();
deopt_id ^= deopt_history.At(i);
if (!deopt_id.IsNull() && (deopt_id.Value() == target)) {
  return false;
}

[Florian Schneider, 2013/05/24 11:53:02]

Done.

+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+
 void LICM::Optimize() {
   const ZoneGrowableArray<BlockEntryInstr*>& loop_headers =
       flow_graph()->loop_headers();
@@ -3525,11 +3548,7 @@
               break;
             }
           }
-          if (inputs_loop_invariant &&
-              !current->IsAssertAssignable() &&
-              !current->IsAssertBoolean()) {
-            // TODO(fschneider): Enable hoisting of Assert-instructions
-            // if it safe to do.
+          if (inputs_loop_invariant && MayHoist(current, pre_header)) {
             Hoist(&it, pre_header, current);
           } else if (current->IsCheckSmi() &&
                      current->InputAt(0)->definition()->IsPhi()) {