DBC: Handle constants correctly in the optimizing backend

runtime/vm/intermediate_language_dbc.cc

Index: runtime/vm/intermediate_language_dbc.cc
diff --git a/runtime/vm/intermediate_language_dbc.cc b/runtime/vm/intermediate_language_dbc.cc
index 859f7d432f3faa8106d55636a27ca97ab0e79fbd..b0f867d3f64939376e1fc987d1ede91247b6bf6e 100644
--- a/runtime/vm/intermediate_language_dbc.cc
+++ b/runtime/vm/intermediate_language_dbc.cc
@@ -338,7 +338,7 @@ EMIT_NATIVE_CODE(LoadClassId, 1, Location::RequiresRegister()) {
 
 
 EMIT_NATIVE_CODE(Constant, 0, Location::RequiresRegister()) {
-  if (compiler->is_optimizing()) {
+  if (compiler->is_optimizing() && locs()->out(0).IsRegister()) {

[Vyacheslav Egorov (Google), 2016/11/03 11:11:50]

We will end up Pushing the constant on the stack here.

Maybe you wanted to do:

if (... is_optimizing()) {
  if (... IsRegister()) {
  }
} else ...

Instead?

[Florian Schneider, 2016/11/03 11:22:59]

Done. Yes, of course. I simplfified the code incorrectly somehow.

     __ LoadConstant(locs()->out(0).reg(), value());
   } else {
     __ PushConstant(value());