Extend bounds check elimination to constant keys.

src/hydrogen-bce.cc

Index: src/hydrogen-bce.cc
diff --git a/src/hydrogen-bce.cc b/src/hydrogen-bce.cc
index 65c2b142c5f3c803a5a3533b57e9c9cb28ba43fa..c72a8c55d865f7bfdf4c7e21c675a710fd3b9ddd 100644
--- a/src/hydrogen-bce.cc
+++ b/src/hydrogen-bce.cc
@@ -54,6 +54,9 @@ class BoundsCheckKey : public ZoneObject {
         constant = HConstant::cast(index->right());
         index_base = index->left();
       }
+    } else if (check->index()->IsConstant()) {
+      index_base = check->block()->graph()->GetConstant0();
+      constant = HConstant::cast(check->index());
     }
 
     if (constant != NULL && constant->HasInteger32Value()) {
@@ -222,41 +225,56 @@ class BoundsCheckBbData: public ZoneObject {
   void MoveIndexIfNecessary(HValue* index_raw,
                             HBoundsCheck* insert_before,
                             HInstruction* end_of_scan_range) {
-    if (!index_raw->IsAdd() && !index_raw->IsSub()) {
-      // index_raw can be HAdd(index_base, offset), HSub(index_base, offset),
-      // or index_base directly. In the latter case, no need to move anything.
-      return;
-    }
-    HArithmeticBinaryOperation* index =
-        HArithmeticBinaryOperation::cast(index_raw);
-    HValue* left_input = index->left();
-    HValue* right_input = index->right();
-    bool must_move_index = false;
-    bool must_move_left_input = false;
-    bool must_move_right_input = false;
-    for (HInstruction* cursor = end_of_scan_range; cursor != insert_before;) {
-      if (cursor == left_input) must_move_left_input = true;
-      if (cursor == right_input) must_move_right_input = true;
-      if (cursor == index) must_move_index = true;
-      if (cursor->previous() == NULL) {
-        cursor = cursor->block()->dominator()->end();
-      } else {
-        cursor = cursor->previous();
+    // index_raw can be HAdd(index_base, offset), HSub(index_base, offset),
+    // HConstant(offset) or index_base directly.
+    // In the latter case, no need to move anything.
+    if (index_raw->IsAdd() || index_raw->IsSub()) {
+      HArithmeticBinaryOperation* index =
+          HArithmeticBinaryOperation::cast(index_raw);
+      HValue* left_input = index->left();
+      HValue* right_input = index->right();
+      bool must_move_index = false;
+      bool must_move_left_input = false;
+      bool must_move_right_input = false;
+      for (HInstruction* cursor = end_of_scan_range; cursor != insert_before;) {
+        if (cursor == left_input) must_move_left_input = true;
+        if (cursor == right_input) must_move_right_input = true;
+        if (cursor == index) must_move_index = true;
+        if (cursor->previous() == NULL) {
+          cursor = cursor->block()->dominator()->end();
+        } else {
+          cursor = cursor->previous();
+        }
+      }
+      if (must_move_index) {
+        index->Unlink();
+        index->InsertBefore(insert_before);
+      }
+      // The BCE algorithm only selects mergeable bounds checks that share
+      // the same "index_base", so we'll only ever have to move constants.
+      if (must_move_left_input) {
+        HConstant::cast(left_input)->Unlink();
+        HConstant::cast(left_input)->InsertBefore(index);
+      }
+      if (must_move_right_input) {
+        HConstant::cast(right_input)->Unlink();
+        HConstant::cast(right_input)->InsertBefore(index);
+      }
+    } else if (index_raw->IsConstant()) {
+      HConstant* index = HConstant::cast(index_raw);
+      bool must_move = false;
+      for (HInstruction* cursor = end_of_scan_range; cursor != insert_before;) {
+        if (cursor == index) must_move = true;
+        if (cursor->previous() == NULL) {
+          cursor = cursor->block()->dominator()->end();
+        } else {
+          cursor = cursor->previous();
+        }
+      }
+      if (must_move) {
+        index->Unlink();
+        index->InsertBefore(insert_before);
       }
-    }
-    if (must_move_index) {
-      index->Unlink();
-      index->InsertBefore(insert_before);
-    }
-    // The BCE algorithm only selects mergeable bounds checks that share
-    // the same "index_base", so we'll only ever have to move constants.
-    if (must_move_left_input) {
-      HConstant::cast(left_input)->Unlink();
-      HConstant::cast(left_input)->InsertBefore(index);
-    }
-    if (must_move_right_input) {
-      HConstant::cast(right_input)->Unlink();
-      HConstant::cast(right_input)->InsertBefore(index);
     }
   }