Remove code that adjusts synced and copied flags in MergeTo.

Review URL: http://codereview.chromium.org/113524

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1998 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/frame-element.h

@@ -152,24 +152,27 @@ class FrameElement BASE_EMBEDDED {
   }
 
   bool Equals(FrameElement other) {
-    if (value_ == other.value_) return true;
-
-    if (type() != other.type() ||
-        is_copied() != other.is_copied() ||
-        is_synced() != other.is_synced() ||
-        !(static_type() == other.static_type())) {
-      return false;
+    uint32_t masked_difference = (value_ ^ other.value_) & ~CopiedField::mask();
+    if (!masked_difference) {
+      // The elements are equal if they agree exactly except on copied field.
+      return true;
+    } else {
+      // If two constants have the same value, and agree otherwise, return true.
+       return !(masked_difference & ~DataField::mask()) &&
+              is_constant() &&
+              handle().is_identical_to(other.handle());
     }
+  }
 
-    if (is_register()) {
-      if (!reg().is(other.reg())) return false;
-    } else if (is_constant()) {
-      if (!handle().is_identical_to(other.handle())) return false;
-    } else if (is_copy()) {
-      if (index() != other.index()) return false;
+  // Test if two FrameElements refer to the same memory or register location.
+  bool SameLocation(FrameElement* other) {
+    if (type() == other->type()) {
+      if (value_ == other->value_) return true;
+      if (is_constant() && handle().is_identical_to(other->handle())) {
+        return true;
+      }
     }
-
-    return true;
+    return false;
   }
 
   // Given a pair of non-null frame element pointers, return one of them
@@ -179,14 +182,7 @@ class FrameElement BASE_EMBEDDED {
     if (!is_valid()) return this;
     if (!other->is_valid()) return other;
 
-    // If they do not have the exact same location we reallocate.
-    bool not_same_location =
-        (type() != other->type()) ||
-        (is_register() && !reg().is(other->reg())) ||
-        (is_constant() && !handle().is_identical_to(other->handle())) ||
-        (is_copy() && index() != other->index());
-    if (not_same_location) return NULL;
-
+    if (!SameLocation(other)) return NULL;
     // If either is unsynced, the result is.  The result static type is
     // the merge of the static types.  It's safe to set it on one of the
     // frame elements, and harmless too (because we are only going to

src/ia32/virtual-frame-ia32.cc

@@ -187,16 +187,6 @@ void VirtualFrame::MakeMergable(int mergable_elements) {
   ASSERT(mergable_elements <= elements_.length());
 
   int start_index = elements_.length() - mergable_elements;
-
-  // The is_copied flags on entry frame elements are expected to be
-  // exact.  Set them for the elements below the water mark.
-  for (int i = 0; i < start_index; i++) {
-    elements_[i].clear_copied();
-    if (elements_[i].is_copy()) {
-      elements_[elements_[i].index()].set_copied();
-    }
-  }
-
   for (int i = start_index; i < elements_.length(); i++) {
     FrameElement element = elements_[i];
 
@@ -272,23 +262,6 @@ void VirtualFrame::MergeTo(VirtualFrame* expected) {
   MergeMoveRegistersToRegisters(expected);
   MergeMoveMemoryToRegisters(expected);
 
-  // Fix any sync flag problems from the bottom-up and make the copied
-  // flags exact.  This assumes that the backing store of copies is
-  // always lower in the frame.
-  for (int i = 0; i < elements_.length(); i++) {
-    FrameElement source = elements_[i];
-    FrameElement target = expected->elements_[i];
-    if (source.is_synced() && !target.is_synced()) {
-      elements_[i].clear_sync();
-    } else if (!source.is_synced() && target.is_synced()) {
-      SyncElementAt(i);
-    }
-    elements_[i].clear_copied();
-    if (elements_[i].is_copy()) {
-      elements_[elements_[i].index()].set_copied();
-    }
-  }
-
   // Adjust the stack pointer downward if necessary.
   if (stack_pointer_ > expected->stack_pointer_) {
     int difference = stack_pointer_ - expected->stack_pointer_;
@@ -314,11 +287,9 @@ void VirtualFrame::MergeMoveRegistersToMemory(VirtualFrame* expected) {
   // of the index of the frame element esi is caching or kIllegalIndex
   // if esi has not been disturbed.
   int esi_caches = kIllegalIndex;
-  // Loop downward from the stack pointer or the top of the frame if
-  // the stack pointer is floating above the frame.
-  int start = Min(static_cast<int>(stack_pointer_), elements_.length() - 1);
-  for (int i = start; i >= 0; i--) {
+  for (int i = elements_.length() - 1; i >= 0; i--) {
     FrameElement target = expected->elements_[i];
+    if (target.is_register()) continue;  // Handle registers later.
     if (target.is_memory()) {
       FrameElement source = elements_[i];
       switch (source.type()) {
@@ -368,8 +339,8 @@ void VirtualFrame::MergeMoveRegistersToMemory(VirtualFrame* expected) {
           }
           break;
       }
-      elements_[i] = target;
     }
+    elements_[i] = target;
   }
 
   if (esi_caches != kIllegalIndex) {
@@ -421,7 +392,8 @@ void VirtualFrame::MergeMoveRegistersToRegisters(VirtualFrame* expected) {
 
 void VirtualFrame::MergeMoveMemoryToRegisters(VirtualFrame* expected) {
   // Move memory, constants, and copies to registers.  This is the
-  // final step and is done from the bottom up so that the backing
+  // final step and since it is not done from the bottom up, but in
+  // register code order, we have special code to ensure that the backing
   // elements of copies are in their correct locations when we
   // encounter the copies.
   for (int i = 0; i < kNumRegisters; i++) {
@@ -430,7 +402,7 @@ void VirtualFrame::MergeMoveMemoryToRegisters(VirtualFrame* expected) {
       FrameElement source = elements_[index];
       FrameElement target = expected->elements_[index];
       Register target_reg = { i };
-      ASSERT(expected->elements_[index].reg().is(target_reg));
+      ASSERT(target.reg().is(target_reg));
       switch (source.type()) {
         case FrameElement::INVALID:  // Fall through.
           UNREACHABLE();

src/virtual-frame.cc

@@ -218,12 +218,6 @@ void VirtualFrame::PrepareMergeTo(VirtualFrame* expected) {
       ASSERT(source.is_valid());
       elements_[i].clear_sync();
     }
-
-    elements_[i].clear_copied();
-    if (elements_[i].is_copy()) {
-      elements_[elements_[i].index()].set_copied();
-    }
-
     // No code needs to be generated to change the static type of an
     // element.
     elements_[i].set_static_type(target.static_type());