Implement basic support for deferred slow path code with calls that save and restore live registers.

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 28b4a649502b0a875866fe37351f599d16bf778b..ea64413883067b5b61a5ef0e4ec04ea03728b0d4 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -205,7 +205,36 @@ bool FlowGraphCompiler::IsNextBlock(BlockEntryInstr* block_entry) const {
 }
 
 
+void FlowGraphCompiler::SaveLiveRegisters(LocationSummary* locs) {
+  // TODO(vegorov): consider saving only caller save (volatile) registers.
+  for (intptr_t reg_idx = 0; reg_idx < kNumberOfCpuRegisters; ++reg_idx) {
+    Register reg = static_cast<Register>(reg_idx);
+    if (locs->live_registers()->Contains(reg)) {
+      assembler()->PushRegister(reg);

[srdjan, 2012/08/15 00:12:03]

How does GC work here, e.g., if a register contains an object? Is it only
because all registers currently contain boxed values and are above the
spill-slot limit, i.e., they are automatically considered objects? Please add
comment, thanks.

[Kevin Millikin (Google), 2012/08/15 08:02:15]

Exactly.  It works now but needs to be changed when we begin deferring more
code.

I'm working on a change to the stackmaps to count these register values, and
when that lands I can safely look for more code to defer.

+    }
+  }
+}
+
+
+void FlowGraphCompiler::RestoreLiveRegisters(LocationSummary* locs) {
+  for (intptr_t reg_idx = kNumberOfCpuRegisters - 1; reg_idx >= 0; --reg_idx) {
+    Register reg = static_cast<Register>(reg_idx);
+    if (locs->live_registers()->Contains(reg)) {
+      assembler()->PopRegister(reg);
+    }
+  }
+}
+
+
+void FlowGraphCompiler::AddSlowPathCode(SlowPathCode* code) {
+  slow_path_code_.Add(code);
+}
+
+
 void FlowGraphCompiler::GenerateDeferredCode() {
+  for (intptr_t i = 0; i < slow_path_code_.length(); i++) {
+    slow_path_code_[i]->EmitNativeCode(this);
+  }
   for (intptr_t i = 0; i < deopt_stubs_.length(); i++) {
     deopt_stubs_[i]->GenerateCode(this, i);
   }
@@ -678,7 +707,7 @@ void FrameRegisterAllocator::AllocateRegisters(Instruction* instr) {
 
   // If this instruction is call spill everything that was not consumed by
   // input locations.
-  if (locs->is_call() || instr->IsBranch() || instr->IsGoto()) {
+  if (locs->contains_call() || instr->IsBranch() || instr->IsGoto()) {
     Spill();
   }