Add new style of string interpolation optimization: new nodes, working constant folding.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 28647)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -6216,6 +6216,75 @@
 }
 
 
+void ConstantPropagator::VisitStringInterpolate(StringInterpolateInstr* instr) {
+  if (IsNonConstant(instr->constant_value())) {
+    // Do not bother with costly analysis if we already know that the
+    // instruction is not a constant.
+    SetValue(instr, non_constant_);
+    return;
+  }
+  // If all inputs are constant strings, numbers, booleans or null, then
+  // constant fold.
+  // TODO(srdjan): Also constant fold an interval of constant arguments.
+  //   v2 <- CreateArray(v0)
+  //   StoreIndexed(v2, v3, v4)   -- v3:constant index, v4: value.
+  //   ..
+  //   v8 <- StaticCall(_interpolate, v2)

[Kevin Millikin (Google), 2013/10/16 15:14:03]

This is not StaticCall anymore.

[srdjan, 2013/10/16 17:46:37]

v8 <- StringInterpolate(v2)

+  CreateArrayInstr* create_array =
+      instr->value()->definition()->AsCreateArray();
+  ASSERT(create_array != NULL);
+
+  // Check if the string interpolation has only constant inputs.
+  for (Value::Iterator it(create_array->input_use_list());
+       !it.Done();
+       it.Advance()) {
+    Instruction* curr = it.Current()->instruction();
+    if (curr != instr) {
+      StoreIndexedInstr* store = curr->AsStoreIndexed();
+      ASSERT(store != NULL);
+      if (!IsConstant(store->value()->definition()->constant_value())) {
+        // Unknown or non-constant.
+        SetValue(instr, store->value()->definition()->constant_value());

[Kevin Millikin (Google), 2013/10/16 15:14:03]

This is the only place where we potentially call SetValue(instr,
unknown_constant_).  We avoid that elsewhere because we don't want to ever move
down the lattice --- we should only call that if it is already unknown_constant.

Maybe we should rewrite here to something like:

const Object& value = ...
if (IsNonConstant(value)) {
  SetValue(instr, non_constant_);
  return;
} else if (IsUnknown(value)) {
  ASSERT(IsUnknown(instr));
  return;
}

[srdjan, 2013/10/16 17:46:37]

Done.

+        return;
+      }
+    }
+  }
+  // Interpolate string at compile time.
+  const Array& value_arr =
+      Array::Handle(Array::New(create_array->num_elements()));
+  // Build array of literal values to interpolate.
+  for (Value::Iterator it(create_array->input_use_list());
+       !it.Done();
+       it.Advance()) {
+    Instruction* curr = it.Current()->instruction();
+    // Skip StringInterpolateInstr.
+    if (curr != instr) {
+      StoreIndexedInstr* store = curr->AsStoreIndexed();
+      ASSERT(store != NULL);
+      Value* index_value = store->index();
+      ASSERT(index_value->BindsToConstant() && index_value->IsSmiValue());
+      const intptr_t ix = Smi::Cast(index_value->BoundConstant()).Value();
+      ASSERT(IsConstant(store->value()->definition()->constant_value()));
+      value_arr.SetAt(ix, store->value()->definition()->constant_value());
+    }
+  }
+  // Build argument array to pass to the interpolation function.
+  const Array& interpolate_arg = Array::Handle(Array::New(1));
+  interpolate_arg.SetAt(0, value_arr);
+  // Call interpolation function.
+  String& concatenated = String::ZoneHandle();
+  concatenated ^=
+      DartEntry::InvokeFunction(instr->CallFunction(), interpolate_arg);
+  if (concatenated.IsUnhandledException()) {
+    SetValue(instr, non_constant_);
+    return;
+  }
+
+  concatenated = Symbols::New(concatenated);
+  SetValue(instr, concatenated);
+}
+
+
 void ConstantPropagator::VisitLoadIndexed(LoadIndexedInstr* instr) {
   SetValue(instr, non_constant_);
 }
@@ -6988,6 +7057,16 @@
         ConstantInstr* constant = graph_->GetConstant(defn->constant_value());
         defn->ReplaceUsesWith(constant);
         i.RemoveCurrentFromGraph();
+        if (defn->IsStringInterpolate()) {
+          CreateArrayInstr* create_array = defn->AsStringInterpolate()->
+              value()->definition()->AsCreateArray();
+          for (Value* use = create_array->input_use_list();
+              use != NULL;
+              use = create_array->input_use_list()) {
+            use->instruction()->RemoveFromGraph();
+          }
+          create_array->RemoveFromGraph();
+        }
       }
     }