Initial implementation of on-stack replacement (OSR).

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 500ca7148997a911f68cdfd8bc779c4868520ea0..b322ce0df29bc6d611243fb4c970d0c120b395c5 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -23,6 +23,7 @@ namespace dart {
 
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, propagate_ic_data);
+DECLARE_FLAG(bool, use_osr);
 
 // Generic summary for call instructions that have all arguments pushed
 // on the stack and return the result in a fixed register EAX.
@@ -2122,6 +2123,13 @@ class CheckStackOverflowSlowPath : public SlowPathCode {
                                   instruction_->deopt_id(),
                                   kStackOverflowRuntimeEntry,
                                   instruction_->locs());
+
+    if (FLAG_use_osr && !compiler->is_optimizing() && instruction_->is_loop()) {
+      // In unoptimized code, record loop stack checks as possible OSR entries.
+      compiler->AddCurrentDescriptor(PcDescriptors::kOsrEntry,
+                                     instruction_->deopt_id(),
+                                     0);  // No token position.
+    }
     compiler->pending_deoptimization_env_ = NULL;
     compiler->RestoreLiveRegisters(instruction_->locs());
     __ jmp(exit_label());
@@ -2139,6 +2147,14 @@ void CheckStackOverflowInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ cmpl(ESP,
           Address::Absolute(Isolate::Current()->stack_limit_address()));
   __ j(BELOW_EQUAL, slow_path->entry_label());
+  if (FLAG_use_osr && !compiler->is_optimizing() && is_loop()) {
+    // In unoptimized code check the usage counter to trigger OSR at loop
+    // stack checks.
+    __ LoadObject(EDI, compiler->parsed_function().function());
+    __ cmpl(FieldAddress(EDI, Function::usage_counter_offset()),
+            Immediate(2 * FLAG_optimization_counter_threshold));
+    __ j(GREATER_EQUAL, slow_path->entry_label());
+  }
   __ Bind(slow_path->exit_label());
 }