Revert "Initial implementation of on-stack replacement (OSR)."

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index 0bd92a7f05f383cf0930a90e53af663736cdb3a8..c93b79a3227b5b4b60470e02b9d4e153fe6a8f38 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -24,7 +24,6 @@ namespace dart {
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, propagate_ic_data);
 DECLARE_FLAG(bool, throw_on_javascript_int_overflow);
-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 RAX.
@@ -2102,13 +2101,6 @@ class CheckStackOverflowSlowPath : public SlowPathCode {
                                   instruction_->deopt_id(),
                                   kStackOverflowRuntimeEntry,
                                   instruction_->locs());
-
-    if (FLAG_use_osr && !compiler->is_optimizing() && instruction_->in_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());
@@ -2128,14 +2120,6 @@ void CheckStackOverflowInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   __ movq(temp, Immediate(Isolate::Current()->stack_limit_address()));
   __ cmpq(RSP, Address(temp, 0));
   __ j(BELOW_EQUAL, slow_path->entry_label());
-  if (FLAG_use_osr && !compiler->is_optimizing() && in_loop()) {
-    // In unoptimized code check the usage counter to trigger OSR at loop
-    // stack checks.
-    __ LoadObject(temp, compiler->parsed_function().function());
-    __ cmpq(FieldAddress(temp, Function::usage_counter_offset()),
-            Immediate(2 * FLAG_optimization_counter_threshold));
-    __ j(GREATER_EQUAL, slow_path->entry_label());
-  }
   __ Bind(slow_path->exit_label());
 }