Collect type feedback for fields.

runtime/vm/compiler.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/code_generator.h"
@@ skipping 94 matching lines @@
               Code::Handle(function.CurrentCode()).EntryPoint());
   }
   function.SwitchToUnoptimizedCode();
   if (FLAG_trace_compiler) {
     OS::Print("--> restoring entry at %#"Px"\n",
               Code::Handle(function.unoptimized_code()).EntryPoint());
   }
 }
 
 
+static ZoneGrowableArray<Field*>* CollectGuardedFieldLoads(
+  FlowGraph* flow_graph) {
+  ZoneGrowableArray<Field*>* result =
+    new ZoneGrowableArray<Field*>(10);
+
+  for (intptr_t i = 1; i < flow_graph->reverse_postorder().length(); i++) {
+    BlockEntryInstr* entry = flow_graph->reverse_postorder()[i];
+    for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
+      LoadFieldInstr* load_field = it.Current()->AsLoadField();
+      if (load_field == NULL || load_field->field() == NULL) continue;
+
+      Field* field = load_field->field();
+      if (field->guarded_cid() == kDynamicCid) continue;

[Kevin Millikin (Google), 2013/03/12 12:14:56]

It's slightly nicer to write:

if (load_field == NULL) continue;
Field* field = load_field->field();
if ((field == NULL) || (field->guarded_cid() == kDynamicCid)) continue;

[Vyacheslav Egorov (Google), 2013/03/12 16:54:40]

Done.

+
+      bool found = false;
+      for (intptr_t j = 0; j < result->length(); j++) {
+        if ((*result)[j]->raw() == field->raw()) {
+          found = true;
+          break;
+        }
+      }
+
+      if (!found) {

[Kevin Millikin (Google), 2013/03/12 12:14:56]

if (!found) result->Add(field);

to match the style you used earlier.

[Vyacheslav Egorov (Google), 2013/03/12 16:54:40]

Aligned all conditions here to use the same line breaking style.

+        result->Add(field);
+      }
+    }
+  }
+
+  return result;
+}
+
+
 // Return false if bailed out.
 static bool CompileParsedFunctionHelper(const ParsedFunction& parsed_function,
                                         bool optimized) {
   TimerScope timer(FLAG_compiler_stats, &CompilerStats::codegen_timer);
   bool is_compiled = false;
   Isolate* isolate = Isolate::Current();
   HANDLESCOPE(isolate);
   ASSERT(isolate->ic_data_array() == Array::null());  // Must be reset to null.
   const intptr_t prev_deopt_id = isolate->deopt_id();
   isolate->set_deopt_id(0);
@@ skipping 35 matching lines @@
       // Transform to SSA (virtual register 0 and no inlining arguments).
       flow_graph->ComputeSSA(0, NULL);
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
     }
 
     if (FLAG_print_flow_graph ||
         (optimized && FLAG_print_flow_graph_optimized)) {
       FlowGraphPrinter::PrintGraph("Before Optimizations", flow_graph);
     }
 
+    ZoneGrowableArray<Field*>* guarded_fields = NULL;
+
     if (optimized) {
       TimerScope timer(FLAG_compiler_stats,
                        &CompilerStats::graphoptimizer_timer,
                        isolate);
 
       FlowGraphOptimizer optimizer(flow_graph);
       optimizer.ApplyICData();
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
 
       // Optimize (a << b) & c patterns. Must occur before
       // 'SelectRepresentations' which inserts conversion nodes.
       // TODO(srdjan): Moved before inlining until environment use list can
       // be used to detect when shift-left is outside the scope of bit-and.
       optimizer.TryOptimizeLeftShiftWithBitAndPattern();
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
 
       // Inlining (mutates the flow graph)
       if (FLAG_use_inlining) {
         TimerScope timer(FLAG_compiler_stats,
                          &CompilerStats::graphinliner_timer);
         FlowGraphInliner inliner(flow_graph);
         inliner.Inline();
         // Use lists are maintained and validated by the inliner.
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
       }
 
+      guarded_fields = CollectGuardedFieldLoads(flow_graph);

[Kevin Millikin (Google), 2013/03/12 12:14:56]

CollectGuardedFieldLoads might be better as a member function on FlowGraph.

Does it need to be here in the pipeline?  I would think as late as possible
would be better.

[Vyacheslav Egorov (Google), 2013/03/12 16:54:40]

Moved to FlowGraph.
Doing it too late might lead to a situtation where load field disappeared from
the graph after it was used for optimization. 

Canonical example would be:

if (this.foo /* not null field foo */ == null) {
  return;
}

load of x.foo should completely disappear (it does not disappear now, but it can
in the future).

+
       // Propagate types and eliminate more type tests.
       if (FLAG_propagate_types) {
         FlowGraphTypePropagator propagator(flow_graph);
         propagator.Propagate();
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
       }
 
       // Use propagated class-ids to optimize further.
       optimizer.ApplyClassIds();
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
@@ skipping 46 matching lines @@
 
       if (FLAG_range_analysis) {
         // We have to perform range analysis after LICM because it
         // optimistically moves CheckSmi through phis into loop preheaders
         // making some phis smi.
         optimizer.InferSmiRanges();
         DEBUG_ASSERT(flow_graph->VerifyUseLists());
       }
 
       // The final canonicalization pass before the code generation.
+      if (FLAG_propagate_types) {

[Kevin Millikin (Google), 2013/03/12 12:14:56]

I think this (and also the other site) needs a comment about what propagate
types will optimize and why we chose this position in the pipeline.  Otherwise
we won't be able to figure it out (and why it's duplicated) in a month.

+        FlowGraphTypePropagator propagator(flow_graph);
+        propagator.Propagate();
+        DEBUG_ASSERT(flow_graph->VerifyUseLists());
+      }
       optimizer.Canonicalize();
       DEBUG_ASSERT(flow_graph->VerifyUseLists());
 
       // Perform register allocation on the SSA graph.
       FlowGraphAllocator allocator(*flow_graph);
       allocator.AllocateRegisters();
 
       if (FLAG_print_flow_graph || FLAG_print_flow_graph_optimized) {
         FlowGraphPrinter::PrintGraph("After Optimizations", flow_graph);
       }
@@ skipping 17 matching lines @@
       const Code& code = Code::Handle(
           Code::FinalizeCode(function, &assembler, optimized));
       code.set_is_optimized(optimized);
       graph_compiler.FinalizePcDescriptors(code);
       graph_compiler.FinalizeDeoptInfo(code);
       graph_compiler.FinalizeStackmaps(code);
       graph_compiler.FinalizeVarDescriptors(code);
       graph_compiler.FinalizeExceptionHandlers(code);
       graph_compiler.FinalizeComments(code);
       graph_compiler.FinalizeStaticCallTargetsTable(code);
+
       if (optimized) {
         CodePatcher::PatchEntry(Code::Handle(function.CurrentCode()));
         function.SetCode(code);
         if (FLAG_trace_compiler) {
           OS::Print("--> patching entry %#"Px"\n",
                     Code::Handle(function.unoptimized_code()).EntryPoint());
         }
+
+        const Array& guarded_fields_arr = Array::Handle(
+            Array::New(guarded_fields->length(), Heap::kOld));

[Kevin Millikin (Google), 2013/03/12 12:14:56]

To fit the pattern, this should be a FinalizeGuardedFieldLoads or some such
member function on the compiler class.

[Vyacheslav Egorov (Google), 2013/03/12 16:54:40]

It does not set anything on the code itself now, so I would prefer to leave it
here.

+        for (intptr_t i = 0; i < guarded_fields->length(); i++) {
+          const Field& field = *(*guarded_fields)[i];
+          guarded_fields_arr.SetAt(i, field);
+          field.RegisterDependentCode(code);
+        }
+        code.set_guarded_fields(guarded_fields_arr);
       } else {
         function.set_unoptimized_code(code);
         function.SetCode(code);
         ASSERT(CodePatcher::CodeIsPatchable(code));
       }
     }
     is_compiled = true;
   } else {
     // We bailed out.
     Error& bailout_error = Error::Handle(
@@ skipping 345 matching lines @@
       Object::Handle(isolate->object_store()->sticky_error());
     isolate->object_store()->clear_sticky_error();
     isolate->set_long_jump_base(base);
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart