Add support for WritableRegister policy in the register allocator.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index d27b20aea1921945bcd55f1d302755eaf05ed376..c28234b65b0964b06bd3bda6f62c0a6929a1c14d 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -920,7 +920,8 @@ LocationSummary* StoreIndexedInstr::MakeLocationSummary() const {
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
   locs->set_in(0, Location::RequiresRegister());
   locs->set_in(1, Location::RequiresRegister());
-  locs->set_in(2, Location::RequiresRegister());
+  locs->set_in(2, value()->NeedsStoreBuffer() ? Location::WritableRegister()
+                                              : Location::RequiresRegister());
   if (receiver_type() == kGrowableObjectArrayCid) {
     locs->set_temp(0, Location::RequiresRegister());
   }
@@ -997,7 +998,9 @@ LocationSummary* StoreInstanceFieldInstr::MakeLocationSummary() const {
   LocationSummary* summary =
       new LocationSummary(kNumInputs, num_temps, LocationSummary::kNoCall);
   summary->set_in(0, Location::RequiresRegister());
-  summary->set_in(1, Location::RequiresRegister());
+  summary->set_in(1,
+      value()->NeedsStoreBuffer() ? Location::WritableRegister()
+                                  : Location::RequiresRegister());
   return summary;
 }
 
@@ -1031,10 +1034,9 @@ void LoadStaticFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 
 LocationSummary* StoreStaticFieldInstr::MakeLocationSummary() const {
   LocationSummary* locs = new LocationSummary(1, 1, LocationSummary::kNoCall);
-  locs->set_in(0, Location::RequiresRegister());
+  locs->set_in(0, value()->NeedsStoreBuffer() ? Location::WritableRegister()
+                                              : Location::RequiresRegister());
   locs->set_temp(0, Location::RequiresRegister());
-  locs->set_out(is_used() ? Location::SameAsFirstInput()
-                          : Location::NoLocation());
   return locs;
 }
 
@@ -1042,7 +1044,6 @@ LocationSummary* StoreStaticFieldInstr::MakeLocationSummary() const {
 void StoreStaticFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register value = locs()->in(0).reg();
   Register temp = locs()->temp(0).reg();
-  ASSERT(!is_used() || (locs()->out().reg() == value));
 
   __ LoadObject(temp, field());
   if (this->value()->NeedsStoreBuffer()) {