VM: Make optimized try-catch work in DBC.

runtime/vm/flow_graph_allocator.cc

Index: runtime/vm/flow_graph_allocator.cc
diff --git a/runtime/vm/flow_graph_allocator.cc b/runtime/vm/flow_graph_allocator.cc
index 7b62e3792c3461fd16262c6b9814eb4e6c5622cc..34e0b0bbfc3c51488235e70c8a8ea9c19d377d68 100644
--- a/runtime/vm/flow_graph_allocator.cc
+++ b/runtime/vm/flow_graph_allocator.cc
@@ -11,6 +11,7 @@
 #include "vm/flow_graph_compiler.h"
 #include "vm/log.h"
 #include "vm/parser.h"
+#include "vm/stack_frame.h"
 
 namespace dart {
 
@@ -612,10 +613,6 @@ void FlowGraphAllocator::BuildLiveRanges() {
     } else if (block->IsCatchBlockEntry()) {
       // Process initial definitions.
       CatchBlockEntryInstr* catch_entry = block->AsCatchBlockEntry();
-#if defined(TARGET_ARCH_DBC)
-      // TODO(vegorov) support try-catch/finally for DBC.
-      flow_graph_.parsed_function().Bailout("FlowGraphAllocator", "Catch");
-#endif
 
       ProcessEnvironmentUses(catch_entry, catch_entry);  // For lazy deopt
 
@@ -631,10 +628,19 @@ void FlowGraphAllocator::BuildLiveRanges() {
       // block start to until the end of the instruction so that they are
       // preserved.
       intptr_t start = catch_entry->start_pos();
-      BlockLocation(Location::RegisterLocation(kExceptionObjectReg),
+#if !defined(TARGET_ARCH_DBC)
+      const Register exception_reg = kExceptionObjectReg;
+      const Register stacktrace_reg = kStackTraceObjectReg;
+#else
+      const intptr_t exception_reg =
+          LocalVarIndex(0, catch_entry->exception_var().index());
+      const intptr_t stacktrace_reg =
+          LocalVarIndex(0, catch_entry->stacktrace_var().index());
+#endif
+      BlockLocation(Location::RegisterLocation(exception_reg),
                     start,
                     ToInstructionEnd(start));
-      BlockLocation(Location::RegisterLocation(kStackTraceObjectReg),
+      BlockLocation(Location::RegisterLocation(stacktrace_reg),
                     start,
                     ToInstructionEnd(start));
     }
@@ -657,8 +663,10 @@ void FlowGraphAllocator::BuildLiveRanges() {
 void FlowGraphAllocator::ProcessInitialDefinition(Definition* defn,
                                                   LiveRange* range,
                                                   BlockEntryInstr* block) {
+#if !defined(TARGET_ARCH_DBC)
   // Save the range end because it may change below.
   intptr_t range_end = range->End();
+#endif
   if (defn->IsParameter()) {
     ParameterInstr* param = defn->AsParameter();
     // Assert that copied and non-copied parameters are mutually exclusive.
@@ -679,7 +687,7 @@ void FlowGraphAllocator::ProcessInitialDefinition(Definition* defn,
       AssignSafepoints(defn, range);
       range->finger()->Initialize(range);
       range->set_assigned_location(Location::RegisterLocation(slot_index));
-      if (range->End() > kNormalEntryPos) {
+      if (block->IsGraphEntry() && (range->End() > kNormalEntryPos)) {
         LiveRange* tail = range->SplitAt(kNormalEntryPos);
         CompleteRange(tail, Location::kRegister);
       }
@@ -726,6 +734,7 @@ void FlowGraphAllocator::ProcessInitialDefinition(Definition* defn,
   }
   ConvertAllUses(range);
   if (defn->IsParameter() && (range->spill_slot().stack_index() >= 0)) {

[Vyacheslav Egorov (Google), 2016/10/04 17:07:54]

I thought we don't support spilling on DBC. How does this work (e.g. where is
the code that ensures that register numbers for live SSA values and register
numbers for spill space for local variables do not intersect?)

[Florian Schneider, 2016/10/04 17:11:02]

You're right. This should be UNREACHABLE() in DBC...

[Vyacheslav Egorov (Google), 2016/10/04 17:55:31]

I am still not completely sure how this stuff manages to work on DBC...

I need to patch this in and look at generated bytecode to convince myself :) I
will do it tomorrow morning. Hope this delay is ok.

+#if !defined(TARGET_ARCH_DBC)
     // Parameters above the frame pointer consume spill slots and are marked
     // in stack maps.
     spill_slots_.Add(range_end);
@@ -738,6 +747,9 @@ void FlowGraphAllocator::ProcessInitialDefinition(Definition* defn,
     spill_slots_.Add(range_end);
     quad_spill_slots_.Add(false);
     untagged_spill_slots_.Add(false);
+#else
+    MarkAsObjectAtSafepoints(range);
+#endif
   }
 }