Experimental: thread live register references to deferred code....

src/codegen.cc

Index: src/codegen.cc
===================================================================
--- src/codegen.cc	(revision 969)
+++ src/codegen.cc	(working copy)
@@ -40,7 +40,7 @@
 DeferredCode::DeferredCode(CodeGenerator* generator)
   : masm_(generator->masm()),
     generator_(generator),
-    enter_(generator),
+    frame_(NULL),
     exit_(generator),
     statement_position_(masm_->last_statement_position()),
     position_(masm_->last_position()) {
@@ -51,6 +51,39 @@
 }
 
 
+void DeferredCode::BranchTo(Condition cc) {
+  // Set the register file and frame based on the first branch to the
+  // deferred code.
+  if (frame_ == NULL) {
+    generator()->allocator()->SaveTo(&registers_);
+    frame_ = new VirtualFrame(generator()->frame());
+  } else {
+    // The frame and register file must match the existing ones.
+    ASSERT(generator()->allocator()->Matches(&registers_));
+    ASSERT(generator()->frame()->Equals(frame_));
+  }
+
+  // Emit the branch.
+  masm_->j(cc, &enter_, not_taken);
+}
+
+
+void DeferredCode::BindExit() {
+  exit_.Bind();
+}
+
+void DeferredCode::ExitIfBound() {
+  if (exit_.is_bound()) {
+    // This backward jump will emit code to merge the code generator's
+    // current frame to the exit frame and then delete the current frame.
+    exit_.Jump();
+  } else {
+    // Don't leak the code generator's current frame.
+    generator()->DeleteFrame();
+  }
+}
+
+
 void CodeGenerator::ProcessDeferred() {
   while (!deferred_.is_empty()) {
     DeferredCode* code = deferred_.RemoveLast();
@@ -63,13 +96,17 @@
       masm->RecordPosition(code->position());
     }
     // Bind labels and generate the code.
-    code->enter()->Bind();
+    masm->bind(code->enter());
+    allocator()->RestoreFrom(code->registers());
+    // Transfer ownership of the deferred code's expected frame to the code
+    // generator.
+    SetFrame(code->frame());
+    code->clear_frame();
+    // For now, we spill before entering any deferred code.
     frame_->SpillAll();
     Comment cmnt(masm, code->comment());
     code->Generate();
-    if (code->exit()->is_bound()) {
-      code->exit()->Jump();
-    }
+    code->ExitIfBound();

[William Hesse, 2008/12/16 09:10:54]

Do we have any deferred code objects that don't return at the end, in which case
this would produce dead code?  Or does JumpTarget::Jump check for an empty
frame?

   }
 }