[builtins] String.prototype.slice as a CSA builtin.

src/code-stub-assembler.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #include "src/code-stub-assembler.h"
 #include "src/code-factory.h"
 #include "src/frames-inl.h"
 #include "src/frames.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 3530 matching lines @@
     a->Goto(&end);
   }
 
   a->BIND(&end);
   return var_result.value();
 }
 
 }  // namespace
 
 Node* CodeStubAssembler::SubString(Node* context, Node* string, Node* from,
-                                   Node* to) {
+                                   Node* to, SubStringFlags flags) {
+  DCHECK(flags == SubStringFlags::NONE ||
+         flags == SubStringFlags::FROM_TO_ARE_BOUNDED);
   VARIABLE(var_result, MachineRepresentation::kTagged);
   ToDirectStringAssembler to_direct(state(), string);
   Label end(this), runtime(this);
 
   // Make sure first argument is a string.
   CSA_ASSERT(this, TaggedIsNotSmi(string));
   CSA_ASSERT(this, IsString(string));
 
   // Make sure that both from and to are non-negative smis.
 
-  GotoIfNot(TaggedIsPositiveSmi(from), &runtime);
-  GotoIfNot(TaggedIsPositiveSmi(to), &runtime);
+  if (flags == SubStringFlags::NONE) {
+    GotoIfNot(TaggedIsPositiveSmi(from), &runtime);
+    GotoIfNot(TaggedIsPositiveSmi(to), &runtime);
+  } else {
+    CSA_ASSERT(this, TaggedIsPositiveSmi(from));
+    CSA_ASSERT(this, TaggedIsPositiveSmi(to));
+  }
 
   Node* const substr_length = SmiSub(to, from);
   Node* const string_length = LoadStringLength(string);
 
   // Begin dispatching based on substring length.
 
   Label original_string_or_invalid_length(this);
   GotoIf(SmiAboveOrEqual(substr_length, string_length),
          &original_string_or_invalid_length);
 
@@ skipping 80 matching lines @@
   // Substrings of length 1 are generated through CharCodeAt and FromCharCode.
   BIND(&single_char);
   {
     Node* char_code = StringCharCodeAt(string, from);
     var_result.Bind(StringFromCharCode(char_code));
     Goto(&end);
   }
 
   BIND(&original_string_or_invalid_length);
   {
-    // Longer than original string's length or negative: unsafe arguments.
-    GotoIf(SmiAbove(substr_length, string_length), &runtime);
+    if (flags == SubStringFlags::NONE) {
+      // Longer than original string's length or negative: unsafe arguments.
+      GotoIf(SmiAbove(substr_length, string_length), &runtime);
+    } else {
+      // with flag SubStringFlags::FROM_TO_ARE_BOUNDED, the only way we can
+      // get here is if substr_length is equal to string_length.
+      CSA_ASSERT(this, SmiEqual(substr_length, string_length));
+    }
 
     // Equal length - check if {from, to} == {0, str.length}.
     GotoIf(SmiAbove(from, SmiConstant(Smi::kZero)), &runtime);
 
     // Return the original string (substr_length == string_length).
 
     Counters* counters = isolate()->counters();
     IncrementCounter(counters->sub_string_native(), 1);
 
     var_result.Bind(string);
@@ skipping 5404 matching lines @@
         formatted.c_str(), TENURED);
     CallRuntime(Runtime::kGlobalPrint, NoContextConstant(),
                 HeapConstant(string));
   }
   CallRuntime(Runtime::kDebugPrint, NoContextConstant(), tagged_value);
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8