Allocate the environment's location backing store during register allocation.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 9eb0767f1938faba685537f430b2724d10b9900e..701408aabbe24c841b9ac44e88d50d881ea0e128 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -2678,13 +2678,11 @@ class BranchInstr : public InstructionWithInputs {
 class Environment : public ZoneAllocated {
  public:
   // Construct an environment by copying from an array of values.
-  // TODO(vegorov): it's absolutely crucial that locations_ backing store
-  // is preallocated and never reallocated.  We use pointers into it
-  // during register allocation.
   explicit Environment(const GrowableArray<Value*>& values,
                        intptr_t fixed_parameter_count)
       : values_(values.length()),
-        locations_(values.length()),
+        location_count_(0),
+        locations_(NULL),
         fixed_parameter_count_(fixed_parameter_count) {
     values_.AddArray(values);
   }
@@ -2693,16 +2691,22 @@ class Environment : public ZoneAllocated {
     return values_;
   }
 
-  void AddLocation(Location value) {
-    locations_.Add(value);
+  void InitializeLocations() {
+    location_count_ = values_.length();

[srdjan, 2012/08/06 22:49:25]

ASSERT(locations_ == NULL), guaranteeing that we do not reallocate locations_ as
we use pointers into it (add that as comment as well).

+    if (location_count_ > 0) {
+      locations_ =
+          Isolate::Current()->current_zone()->Alloc<Location>(location_count_);

[srdjan, 2012/08/06 22:49:25]

Please initialize locations_ with default Location values.

+    }
   }
 
   Location LocationAt(intptr_t ix) const {
+    ASSERT((ix >= 0) && (ix < location_count_));

[srdjan, 2012/08/06 22:49:25]

ASSERT(locations_ != NULL) .

     return locations_[ix];
   }
 
   Location* LocationSlotAt(intptr_t ix) const {
-    return & locations_[ix];
+    ASSERT((ix >= 0) && (ix < location_count_));

[srdjan, 2012/08/06 22:49:25]

ditto

+    return &locations_[ix];
   }
 
   intptr_t fixed_parameter_count() const {
@@ -2713,7 +2717,8 @@ class Environment : public ZoneAllocated {
 
  private:
   GrowableArray<Value*> values_;
-  GrowableArray<Location> locations_;
+  intptr_t location_count_;
+  Location* locations_;
   const intptr_t fixed_parameter_count_;
 
   DISALLOW_COPY_AND_ASSIGN(Environment);