Split LoadStatic into two instructions: load static filed, load value.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
===================================================================
--- runtime/vm/intermediate_language_ia32.cc	(revision 24013)
+++ runtime/vm/intermediate_language_ia32.cc	(working copy)
@@ -1759,16 +1759,22 @@
 
 
 LocationSummary* LoadStaticFieldInstr::MakeLocationSummary() const {
-  return LocationSummary::Make(0,
-                               Location::RequiresRegister(),
-                               LocationSummary::kNoCall);
+  const intptr_t kNumInputs = 1;
+  const intptr_t kNumTemps = 0;
+  LocationSummary* summary =
+      new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
+  summary->set_in(0, Location::RequiresRegister());
+  // By specifying same register as input, our simple register allocator can
+  // generate better code.

[Florian Schneider, 2013/06/14 08:55:05]

Side note: We have a similar issue for LoadField: Ideally, I think we want to
have a policy that allows re-using the input as result, but does not enforce it
(MayUseSameAsFirst)

It may be good to use a different register because of register hints sometimes,
other times re-using the same register saves freeing up another register.

[srdjan, 2013/06/14 14:00:04]

Yes, that is a good idea. I think that would help especially ia32 quite a bit.
Next CL.

+  summary->set_out(Location::SameAsFirstInput());
+  return summary;
 }
 
 
 void LoadStaticFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  Register field = locs()->in(0).reg();
   Register result = locs()->out().reg();
-  __ LoadObject(result, field());
-  __ movl(result, FieldAddress(result, Field::value_offset()));
+  __ movl(result, FieldAddress(field, Field::value_offset()));

[Florian Schneider, 2013/06/14 08:55:05]

Do static fields move in memory due to GC?

If not, we could just load from the absolute address directly? This way there is
also no need for an input register and tuning for the best register policy.

[srdjan, 2013/06/14 14:00:04]

They don't now, but they will.

 }