Don't optimize away static field initialization when precompiling.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 8754ecfe48fe31b2a08e3ff188e891276f82b49b..c526fe03b14e5f67f74c60301b87fe0e749e7e10 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -37,6 +37,8 @@ DEFINE_FLAG(bool, two_args_smi_icd, true,
     "Generate special IC stubs for two args Smi operations");
 DEFINE_FLAG(bool, unbox_numeric_fields, true,
     "Support unboxed double and float32x4 fields.");
+DEFINE_FLAG(bool, fields_may_be_reset, false,
+            "Don't optimize away static field initialization");

[hausner, 2015/09/10 22:55:12]

The flag name and the description are quite different. It would be nice to have
a comment explaining what is going on. (Why can't the initializers be optimized
away?)

OTOH, do we really need a separate flag for this? I'm not familiar with all the
different flags we have that affect the VM when pre-compilation is used, but
maybe this can be combined with one of the other flags.

[rmacnak, 2015/09/11 00:07:13]

Added:

  // When precompiling, the fact that a field is currently initialized does not
  // make it safe to omit code that checks if the field needs initialization
  // because the field will be reset so it starts uninitialized in the process
  // running the precompiled code. We must be prepared to reinitialize fields.
--precompile is a flag handler that flips a number of other flags. Having
separate flags lets us test alternate compilations independent of
precompilation.

 DECLARE_FLAG(bool, eliminate_type_checks);
 DECLARE_FLAG(bool, trace_optimization);
 DECLARE_FLAG(bool, throw_on_javascript_int_overflow);
@@ -385,7 +387,7 @@ Instruction* InitStaticFieldInstr::Canonicalize(FlowGraph* flow_graph) {
   const bool is_initialized =
       (field_.StaticValue() != Object::sentinel().raw()) &&
       (field_.StaticValue() != Object::transition_sentinel().raw());
-  return is_initialized ? NULL : this;
+  return is_initialized && !FLAG_fields_may_be_reset ? NULL : this;
 }