Indirectly dispatch all backtracking jumps through the same block.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 250651e3bb61c3cee1b4fec56e64c5add6da63d7..17e86baedb6d2c771b6198e9d64adebf5f2ea91a 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -2530,6 +2530,41 @@ void TargetEntryInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 }
 
 
+void IndirectGotoInstr::ComputeOffsetTable(Isolate* isolate) {
+  if (GetBlock()->offset() < 0) {
+    // Don't generate a table when contained in an unreachable block.
+    return;
+  }
+  ASSERT(SuccessorCount() == offsets_.Capacity());
+  offsets_.SetLength(SuccessorCount());
+  for (intptr_t i = 0; i < SuccessorCount(); i++) {
+    TargetEntryInstr* target = SuccessorAt(i);
+    intptr_t offset = target->offset();
+
+    // The intermediate block might be compacted, if so, use the indirect entry.
+    if (offset < 0) {
+      // Optimizations might have modified the immediate target block, but it
+      // must end with a goto to the indirect entry. Also, we can't use
+      // last_instruction because 'target' is compacted/unreachable.
+      Instruction* last = target->next();
+      while (last != NULL && !last->IsGoto()) {
+        last = last->next();
+      }
+      ASSERT(last);
+      IndirectEntryInstr* ientry =
+          last->AsGoto()->successor()->AsIndirectEntry();
+      ASSERT(ientry != NULL);
+      ASSERT(ientry->indirect_id() == i);
+      offset = ientry->offset();
+    }
+
+    ASSERT(offset > 0);
+    offset -= Assembler::EntryPointToPcMarkerOffset();
+    offsets_.SetAt(i, Smi::ZoneHandle(isolate, Smi::New(offset)));
+  }
+}
+
+
 LocationSummary* IndirectEntryInstr::MakeLocationSummary(
     Isolate* isolate, bool optimizing) const {
   return JoinEntryInstr::MakeLocationSummary(isolate, optimizing);