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

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

This reapplies SVN r24024 with a bugfix.

After OSR compilation, restore the pre-OSR code (which might be already
optimized) rather than the unoptimized code (which might have its entry
patched).  When the optimized code entry is patched it is only safe to call
it as a static call, not as an instance call.

R=fschneider@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24088

[Kevin Millikin (Google), 2013-06-17 08:51:29]

The only diff from the original version is:

--- a/runtime/vm/code_generator.cc
+++ b/runtime/vm/code_generator.cc
@@ -1287,20 +1287,21 @@ DEFINE_RUNTIME_ENTRY(StackOverflow, 0) {
                 osr_id);
     }
 
+    const Code& original_code = Code::Handle(function.CurrentCode());
     const Error& error =
         Error::Handle(Compiler::CompileOptimizedFunction(function, osr_id));
     if (!error.IsNull()) Exceptions::PropagateError(error);
 
     const Code& optimized_code = Code::Handle(function.CurrentCode());
-    // The current code will not be optimized in the case that the compiler
-    // bailed out (not an error) during OSR compilation.
-    if (optimized_code.is_optimized()) {
+    // The current code will not be changed in the case that the compiler
+    // bailed out during OSR compilation.
+    if (optimized_code.raw() != original_code.raw()) {
       // The OSR code does not work for calling the function, so restore the
       // unoptimized code.  Patch the stack frame to return into the OSR
       // code.
-      intptr_t optimized_entry =
+      uword optimized_entry =
           Instructions::Handle(optimized_code.instructions()).EntryPoint();
-      function.SetCode(Code::Handle(function.unoptimized_code()));
+      function.SetCode(original_code);
       frame->set_pc(optimized_entry);
     }
   }

[Florian Schneider, 2013-06-17 09:00:26]

lgtm

[Kevin Millikin (Google), 2013-06-17 11:05:35]

Committed patchset #1 manually as r24088 (presubmit successful).