[strong] Simplify (and sortof optimize) string addition for strong mode.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 559eca6e5847eb8d3503a1f2426a74e60d5c8026..9354266d768c656bfe5db0e1acb89d9cb5aedd04 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -10914,29 +10914,35 @@ HValue* HGraphBuilder::BuildBinaryOperation(
     }
 
     // Convert left argument as necessary.
-    if (left_type->Is(Type::Number()) && !is_strong(strength)) {
+    if (!left_type->Is(Type::String())) {
       DCHECK(right_type->Is(Type::String()));
-      left = BuildNumberToString(left, left_type);
-    } else if (!left_type->Is(Type::String())) {
-      DCHECK(right_type->Is(Type::String()));
-      HValue* function = AddLoadJSBuiltin(
-          is_strong(strength) ? Builtins::STRING_ADD_RIGHT_STRONG
-                              : Builtins::STRING_ADD_RIGHT);
-      Add<HPushArguments>(left, right);
-      return AddUncasted<HInvokeFunction>(function, 2);
+      if (is_strong(strength)) {
+        // In strong mode, if the left hand side of an additition is a string,

[Jarin, 2015/08/13 06:23:50]

additition -> addition (Here and below.)

[Benedikt Meurer, 2015/08/13 06:31:13]

Done.

+        // the right hand side must be a string too.
+        left = BuildCheckString(left);
+      } else if (left_type->Is(Type::Number())) {
+        left = BuildNumberToString(left, left_type);
+      } else {
+        HValue* function = AddLoadJSBuiltin(Builtins::STRING_ADD_RIGHT);
+        Add<HPushArguments>(left, right);
+        return AddUncasted<HInvokeFunction>(function, 2);
+      }
     }
 
     // Convert right argument as necessary.
-    if (right_type->Is(Type::Number()) && !is_strong(strength)) {
+    if (!right_type->Is(Type::String())) {
       DCHECK(left_type->Is(Type::String()));
-      right = BuildNumberToString(right, right_type);
-    } else if (!right_type->Is(Type::String())) {
-      DCHECK(left_type->Is(Type::String()));
-      HValue* function = AddLoadJSBuiltin(is_strong(strength)
-                                              ? Builtins::STRING_ADD_LEFT_STRONG
-                                              : Builtins::STRING_ADD_LEFT);
-      Add<HPushArguments>(left, right);
-      return AddUncasted<HInvokeFunction>(function, 2);
+      if (is_strong(strength)) {
+        // In strong mode, if the right hand side of an additition is a string,
+        // the left hand side must be a string too.
+        right = BuildCheckString(right);
+      } else if (right_type->Is(Type::Number())) {
+        right = BuildNumberToString(right, right_type);
+      } else {
+        HValue* function = AddLoadJSBuiltin(Builtins::STRING_ADD_LEFT);
+        Add<HPushArguments>(left, right);
+        return AddUncasted<HInvokeFunction>(function, 2);
+      }
     }
 
     // Fast paths for empty constant strings.