Remove register counts from VirtualFrame, use register indices instead.

src/virtual-frame.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 39 matching lines @@
 
 
 // When cloned, a frame is a deep copy of the original.
 VirtualFrame::VirtualFrame(VirtualFrame* original)
     : cgen_(original->cgen_),
       masm_(original->masm_),
       elements_(original->elements_.length()),
       parameter_count_(original->parameter_count_),
       local_count_(original->local_count_),
       stack_pointer_(original->stack_pointer_),
-      frame_pointer_(original->frame_pointer_),
-      frame_registers_(original->frame_registers_) {
+      frame_pointer_(original->frame_pointer_) {
   // Copy all the elements from the original.
   for (int i = 0; i < original->elements_.length(); i++) {
     elements_.Add(original->elements_[i]);
   }
   for (int i = 0; i < kNumRegisters; i++) {
     register_locations_[i] = original->register_locations_[i];
   }
 }
 
 
@@ skipping 73 matching lines @@
 
   for (int i = 0; i < count; i++) {
     FrameElement last = elements_.RemoveLast();
     if (last.is_register()) {
       // A hack to properly count register references for the code
       // generator's current frame and also for other frames.  The
       // same code appears in PrepareMergeTo.
       if (cgen_->frame() == this) {
         Unuse(last.reg());
       } else {
-        frame_registers_.Unuse(last.reg());
         register_locations_[last.reg().code()] = kIllegalIndex;
       }
     }
   }
 }
 
 
 void VirtualFrame::Use(Register reg, int index) {
-  ASSERT(frame_registers_.count(reg) == 0);
   ASSERT(register_locations_[reg.code()] == kIllegalIndex);
   register_locations_[reg.code()] = index;
-  frame_registers_.Use(reg);
   cgen_->allocator()->Use(reg);
 }
 
 
 void VirtualFrame::Unuse(Register reg) {
-  ASSERT(frame_registers_.count(reg) == 1);
   ASSERT(register_locations_[reg.code()] != kIllegalIndex);
   register_locations_[reg.code()] = kIllegalIndex;
-  frame_registers_.Unuse(reg);
   cgen_->allocator()->Unuse(reg);
 }
 
 
 void VirtualFrame::Spill(Register target) {
-  if (!frame_registers_.is_used(target)) return;
-  for (int i = 0; i < elements_.length(); i++) {
-    if (elements_[i].is_register() && elements_[i].reg().is(target)) {
-      SpillElementAt(i);
-    }
+  if (is_used(target)) {
+    SpillElementAt(register_index(target));
   }
 }
 
 
 // Spill any register if possible, making its external reference count zero.
 Register VirtualFrame::SpillAnyRegister() {
   // Find the leftmost (ordered by register code), least
   // internally-referenced register whose internal reference count matches
   // its external reference count (so that spilling it from the frame frees
   // it for use).
-  int min_count = kMaxInt;
-  int best_register_code = no_reg.code_;
-
+  // This function must be called with no free registers - all counts
+  // in the CodeGenerator's Allocator must be above 0.

[Kevin Millikin (Chromium), 2009/03/25 09:54:11]

I don't like this comment.  It's not really a true precondition (the function
still works fine otherwise), and if it were a precondition it shouldn't be
buried here in the implementation.

[William Hesse, 2012/05/07 09:35:42]

Done.

   for (int i = 0; i < kNumRegisters; i++) {
-    int count = frame_registers_.count(i);
-    if (count < min_count && count == cgen_->allocator()->count(i)) {
-      min_count = count;
-      best_register_code = i;
+    if (is_used(i) && cgen_->allocator()->count(i) == 1) {
+      Register result = { i };
+      Spill(result);
+      ASSERT(!cgen_->allocator()->is_used(result));
+      return result;
     }
   }
-
-  Register result = { best_register_code };
-  if (result.is_valid()) {
-    Spill(result);
-    ASSERT(!cgen_->allocator()->is_used(result));
-  }
-  return result;
+  return no_reg;
 }
 
 
 // Make the type of the element at a given index be MEMORY.
 void VirtualFrame::SpillElementAt(int index) {
   if (!elements_[index].is_valid()) return;
 
   SyncElementAt(index);
   // The element is now in memory.  Its copied flag is preserved.
   FrameElement new_element = FrameElement::MemoryElement();
@@ skipping 48 matching lines @@
       // No code needs to be generated to move values to memory if
       // they are already synced.  We perform those moves here, before
       // merging.
       if (source.is_register()) {
         // If the frame is the code generator's current frame, we have
         // to decrement both the frame-internal and global register
         // counts.
         if (cgen_->frame() == this) {
           Unuse(source.reg());
         } else {
-          frame_registers_.Unuse(source.reg());
           register_locations_[source.reg().code()] = kIllegalIndex;
         }
       }
       elements_[i] = target;
     } else if (target.is_register() && !target.is_synced() &&
                !source.is_memory()) {
       // If an element's target is a register that doesn't need to be
       // synced, and the element is not in memory, then the sync state
       // of the element is irrelevant.  We clear the sync bit.
       ASSERT(source.is_valid());
@@ skipping 90 matching lines @@
                     && original.handle().is_identical_to(value->handle());
   if (same_register || same_constant) {
     value->Unuse();
     return;
   }
 
   InvalidateFrameSlotAt(frame_index);
 
   FrameElement new_element;
   if (value->is_register()) {
-    // There are two cases depending no whether the register already
-    // occurs in the frame or not.
-    if (register_count(value->reg()) == 0) {
-      Use(value->reg(), frame_index);
-      elements_[frame_index] =
-          FrameElement::RegisterElement(value->reg(),
-                                        FrameElement::NOT_SYNCED);
-    } else {
-      int i = 0;
-      for (; i < elements_.length(); i++) {
-        if (elements_[i].is_register() && elements_[i].reg().is(value->reg())) {
-          break;
-        }
-      }
-      ASSERT(i < elements_.length());
-
+    if (is_used(value->reg())) {
+      // The register already appears on the frame.  Either the existing
+      // register element, or the new element at frame_index, must be made
+      // a copy.
+      int i = register_index(value->reg());
       if (i < frame_index) {
-        // The register backing store is lower in the frame than its copy.
+        // The register FrameElement is lower in the frame than the new copy.
         elements_[frame_index] = CopyElementAt(i);
       } else {
         // There was an early bailout for the case of setting a
         // register element to itself.
         ASSERT(i != frame_index);
         elements_[frame_index] = elements_[i];
         elements_[i] = CopyElementAt(frame_index);
         if (elements_[frame_index].is_synced()) {
           elements_[i].set_sync();
         }
         elements_[frame_index].clear_sync();
         register_locations_[value->reg().code()] = frame_index;
         for (int j = i + 1; j < elements_.length(); j++) {
           if (elements_[j].is_copy() && elements_[j].index() == i) {
             elements_[j].set_index(frame_index);
           }
         }
       }
+    } else {
+      // The register value->reg() was not already used on the frame.
+      Use(value->reg(), frame_index);
+      elements_[frame_index] =
+          FrameElement::RegisterElement(value->reg(),
+                                        FrameElement::NOT_SYNCED);
     }
   } else {
     ASSERT(value->is_constant());
     elements_[frame_index] =
         FrameElement::ConstantElement(value->handle(),
                                       FrameElement::NOT_SYNCED);
   }
   value->Unuse();
 }
 
@@ skipping 51 matching lines @@
       // a different signature.
       UNREACHABLE();
       break;
   }
   PrepareForCall(spilled_args, dropped_args);
   return RawCallCodeObject(code, rmode);
 }
 
 
 void VirtualFrame::Push(Register reg) {
-  FrameElement new_element;
-  if (register_count(reg) == 0) {
+  if (is_used(reg)) {
+    elements_.Add(CopyElementAt(register_index(reg)));
+  } else {
     Use(reg, elements_.length());
-    new_element =
-        FrameElement::RegisterElement(reg, FrameElement::NOT_SYNCED);
-  } else {
-    for (int i = 0; i < elements_.length(); i++) {
-      FrameElement element = elements_[i];
-      if (element.is_register() && element.reg().is(reg)) {
-        new_element = CopyElementAt(i);
-        break;
-      }
-    }
+    elements_.Add(FrameElement::RegisterElement(reg, FrameElement::NOT_SYNCED));
   }
-  elements_.Add(new_element);
 }
 
 
 void VirtualFrame::Push(Handle<Object> value) {
   elements_.Add(FrameElement::ConstantElement(value,
                                               FrameElement::NOT_SYNCED));
 }
 
 
 void VirtualFrame::Push(Result* result) {
@@ skipping 37 matching lines @@
 #ifdef DEBUG
   // These are sanity checks in debug builds, but we do not need to
   // use them to distinguish frames at merge points.
   if (cgen_ != other->cgen_) return false;
   if (masm_ != other->masm_) return false;
   if (parameter_count_ != other->parameter_count_) return false;
   if (local_count_ != other->local_count_) return false;
   if (frame_pointer_ != other->frame_pointer_) return false;
 
   for (int i = 0; i < kNumRegisters; i++) {
-    if (frame_registers_.count(i) != other->frame_registers_.count(i)) {
-      return false;
-    }
     if (register_locations_[i] != other->register_locations_[i]) {
       return false;
     }
   }
   if (elements_.length() != other->elements_.length()) return false;
 #endif
   if (stack_pointer_ != other->stack_pointer_) return false;
   for (int i = 0; i < elements_.length(); i++) {
     if (!elements_[i].Equals(other->elements_[i])) return false;
   }
 
   return true;
 }
 
 } }  // namespace v8::internal