[v8-dev] Optimize array literal boilerplate copy for fast cases. (issue 8590026)

[danno]

Reviewers: Jakob,

Message:
ptal
Description:
Optimize array literal boilerplate copy for fast cases.

R=jkumme...@chromium.org
BUG=none
TEST=none


Please review this at http://codereview.chromium.org/8590026/

SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge

Affected files:
  M src/ia32/full-codegen-ia32.cc
  M src/x64/full-codegen-x64.cc


Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index  
10a3422ea1d429f899bd4ee8ae056e1ee244ee31..c329dc72f85964da164b98f251c74000e4372a01  
100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1477,6 +1477,8 @@ void  
FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   int length = subexprs->length();
   Handle<FixedArray> constant_elements = expr->constant_elements();
   ASSERT_EQ(2, constant_elements->length());
+  ElementsKind constant_elements_kind =
+       
static_cast<ElementsKind>(Smi::cast(constant_elements->get(0))->value());
   Handle<FixedArrayBase> constant_elements_values(
       FixedArrayBase::cast(constant_elements->get(1)));

@@ -1497,8 +1499,19 @@ void  
FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
       __ IncrementCounter(isolate()->counters()->cow_arrays_created_stub(),
                           1);
     }
-    FastCloneShallowArrayStub stub(
-        FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS, length);
+    FastCloneShallowArrayStub::Mode mode =
+        FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS;
+    if (constant_elements_kind == FAST_ELEMENTS) {
+      // If the elements are already FAST_ELEMENTS, the boilerplate cannot
+      // change, so it's possible to specialize the stub in advance.
+      if (constant_elements_values->map() ==
+          isolate()->heap()->fixed_cow_array_map()) {
+        mode = FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS;
+      } else {
+        mode = FastCloneShallowArrayStub::CLONE_ELEMENTS;
+      }
+    }
+    FastCloneShallowArrayStub stub(mode, length);
     __ CallStub(&stub);
   }

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index  
9a001266c9f3b8b56d888058792584cac25d87e7..83888cf9345c925ad0fabca788829df5bc84db13  
100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1502,8 +1502,19 @@ void  
FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
       __ IncrementCounter(isolate()->counters()->cow_arrays_created_stub(),
                           1);
     }
-    FastCloneShallowArrayStub stub(
-        FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS, length);
+    FastCloneShallowArrayStub::Mode mode =
+        FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS;
+    if (constant_elements_kind == FAST_ELEMENTS) {
+      // If the elements are already FAST_ELEMENTS, the boilerplate cannot
+      // change, so it's possible to specialize the stub in advance.
+      if (constant_elements_values->map() ==
+          isolate()->heap()->fixed_cow_array_map()) {
+        mode = FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS;
+      } else {
+        mode = FastCloneShallowArrayStub::CLONE_ELEMENTS;
+      }
+    }
+    FastCloneShallowArrayStub stub(mode, length);
     __ CallStub(&stub);
   }



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