Optimize string interpolation by running it at compile time if all inputs are constant. This is don…

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 28173)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -6035,7 +6035,78 @@
 
 
 void ConstantPropagator::VisitStaticCall(StaticCallInstr* instr) {
-  SetValue(instr, non_constant_);
+  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;
+  }
+  MethodRecognizer::Kind recognized_kind =
+      MethodRecognizer::RecognizeKind(instr->function());
+  if (recognized_kind == MethodRecognizer::kStringBaseInterpolate) {
+    // static String _interpolate(List values)
+    //
+    // Code for calling interpolate is generated by the compiler:
+    //   v2 <- CreateArray(v0)
+    //   StoreIndexed(v2, v3, v4)   -- v3:constant index, v4: value.
+    //   ..
+    //   PushArgument(v2)
+    //   v8 <- StaticCall(_interpolate, v2)
+    // Detect that all values are constant, interpolate at compile
+    // time.
+    ASSERT(instr->ArgumentCount() == 1);
+    CreateArrayInstr* create_array = instr->ArgumentAt(0)->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();
+      StoreIndexedInstr* store = curr->AsStoreIndexed();
+      // 'store' is NULL fir PushArgument instruction: skip it.
+      if ((store != NULL) &&
+          (IsNonConstant(store->value()->definition()->constant_value()))) {
+        SetValue(instr, non_constant_);
+        return;
+      }
+    }
+    // Interpolate string at compile time.
+    const Array& value_arr =
+        Array::Handle(Array::New(create_array->num_elements()));
+    // Build the array of literal values to interpolate, abort if a value is
+    // not literal.
+    for (Value::Iterator it(create_array->input_use_list());
+         !it.Done();
+         it.Advance()) {
+      Instruction* curr = it.Current()->instruction();
+      StoreIndexedInstr* store = curr->AsStoreIndexed();
+      if (store == NULL) {
+        ASSERT(curr == instr->PushArgumentAt(0));
+      } else {
+        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->function(), interpolate_arg);
+    if (concatenated.IsUnhandledException()) {
+      SetValue(instr, non_constant_);
+      return;
+    }
+
+    concatenated = Symbols::New(concatenated);
+    SetValue(instr, concatenated);
+  } else {
+    SetValue(instr, non_constant_);
+  }
 }
 
 
@@ -6868,6 +6939,27 @@
 }
 
 
+// Code for calling interpolate is generated by the compiler:
+//   v2 <- CreateArray(v0)
+//   StoreIndexed(v2, v3, v4)   -- v3:constant index, v4: value.
+//   ..
+//   PushArgument(v2)
+//   v8 <- StaticCall(_interpolate, v2)
+// Remove the inputs.
+void ConstantPropagator::RemoveInterpolationInputs(
+    const StaticCallInstr& call) {
+  ASSERT(call.ArgumentCount() == 1);
+  CreateArrayInstr* create_array = call.ArgumentAt(0)->AsCreateArray();
+  ASSERT(create_array != NULL);
+  for (Value* use = create_array->input_use_list();
+      use != NULL;
+      use = create_array->input_use_list()) {
+    use->instruction()->RemoveFromGraph();
+  }
+  create_array->RemoveFromGraph();
+}
+
+
 void ConstantPropagator::Transform() {
   if (FLAG_trace_constant_propagation) {
     OS::Print("\n==== Before constant propagation ====\n");
@@ -6975,6 +7067,13 @@
         ConstantInstr* constant = graph_->GetConstant(defn->constant_value());
         defn->ReplaceUsesWith(constant);
         i.RemoveCurrentFromGraph();
+        if (defn->IsStaticCall()) {
+          MethodRecognizer::Kind recognized_kind =
+              MethodRecognizer::RecognizeKind(defn->AsStaticCall()->function());
+          if (recognized_kind == MethodRecognizer::kStringBaseInterpolate) {
+            RemoveInterpolationInputs(*defn->AsStaticCall());
+          }
+        }
       }
     }