Revert "Revert "Introduce Goto instructions to the flow graph.""

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 8cc93e3e980e69d44179ac9d65a0f14058d86dec..f250a5761ff8a421ae53a4f3974c22043f6e1634 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -258,6 +258,22 @@ void ThrowInstr::SetInputAt(intptr_t i, Value* value) {
 }
 
 
+intptr_t GotoInstr::InputCount() const {
+  return 0;
+}
+
+
+Value* GotoInstr::InputAt(intptr_t i) const {
+  UNREACHABLE();
+  return NULL;
+}
+
+
+void GotoInstr::SetInputAt(intptr_t i, Value* value) {
+  UNREACHABLE();
+}
+
+
 intptr_t ReturnInstr::InputCount() const {
   return 1;
 }
@@ -487,7 +503,9 @@ void BlockEntryInstr::DiscoverBlocks(
            !next_instr->IsBranch()) {
       if (vars != NULL) next_instr->RecordAssignedVars(vars);
       set_last_instruction(next_instr);
-      next_instr = next_instr->next();
+      GotoInstr* goto_instr = next_instr->AsGoto();
+      next_instr =
+          (goto_instr != NULL) ? goto_instr->successor() : next_instr->next();
     }
   }
   if (next_instr != NULL) {
@@ -539,13 +557,15 @@ void JoinEntryInstr::InsertPhi(intptr_t var_index, intptr_t var_count) {
 
 
 intptr_t Instruction::SuccessorCount() const {
-  ASSERT(next() == NULL || next()->IsBlockEntry());
-  return (next() != NULL) ? 1 : 0;
+  return 0;
 }
 
 
 BlockEntryInstr* Instruction::SuccessorAt(intptr_t index) const {
-  return next()->AsBlockEntry();
+  // Called only if index is in range.  Only control-transfer instructions
+  // can have non-zero successor counts and they override this function.
+  UNREACHABLE();
+  return NULL;
 }
 
 
@@ -573,6 +593,22 @@ BlockEntryInstr* BranchInstr::SuccessorAt(intptr_t index) const {
 }
 
 
+intptr_t GotoInstr::SuccessorCount() const {
+  return 1;
+}
+
+
+BlockEntryInstr* GotoInstr::SuccessorAt(intptr_t index) const {
+  ASSERT(index == 0);
+  return successor();
+}
+
+
+void Instruction::Goto(JoinEntryInstr* entry) {
+  set_next(new GotoInstr(entry));
+}
+
+
 // ==== Support for propagating static type.
 RawAbstractType* ConstantVal::StaticType() const {
   if (value().IsInstance()) {
@@ -987,6 +1023,20 @@ void ReThrowInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
 }
 
 
+LocationSummary* GotoInstr::MakeLocationSummary() const {
+  return new LocationSummary(0, 0);
+}
+
+
+void GotoInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  // We can fall through if the successor is the next block in the list.
+  // Otherwise, we need a jump.
+  if (!compiler->IsNextBlock(successor())) {
+    __ jmp(compiler->GetBlockLabel(successor()));
+  }
+}
+
+
 LocationSummary* BranchInstr::MakeLocationSummary() const {
   if (is_fused_with_comparison()) {
     return fused_with_comparison_->locs();