Change the handling of stack check on backward branches

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 7550809ae105f2a6c2e598ef191a93884767ff9c..ce9915b90403ba2641f0e381bdf7b51556cd3430 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -163,14 +163,13 @@ void HBasicBlock::Finish(HControlInstruction* end) {
 }
 
 
-void HBasicBlock::Goto(HBasicBlock* block, bool include_stack_check) {
+void HBasicBlock::Goto(HBasicBlock* block) {
   if (block->IsInlineReturnTarget()) {
     AddInstruction(new(zone()) HLeaveInlined);
     last_environment_ = last_environment()->outer();
   }
   AddSimulate(AstNode::kNoNumber);
   HGoto* instr = new(zone()) HGoto(block);
-  instr->set_include_stack_check(include_stack_check);
   Finish(instr);
 }
 
@@ -576,7 +575,7 @@ HBasicBlock* HGraphBuilder::CreateLoop(IterationStatement* statement,
                                        HBasicBlock* body_exit,
                                        HBasicBlock* loop_successor,
                                        HBasicBlock* break_block) {
-  if (body_exit != NULL) body_exit->Goto(loop_entry, true);
+  if (body_exit != NULL) body_exit->Goto(loop_entry);
   loop_entry->PostProcessLoopHeader(statement);
   if (break_block != NULL) {
     if (loop_successor != NULL) loop_successor->Goto(break_block);
@@ -1234,8 +1233,6 @@ class HStackCheckEliminator BASE_EMBEDDED {
   void Process();
 
  private:
-  void RemoveStackCheck(HBasicBlock* block);
-
   HGraph* graph_;
 };
 
@@ -1254,7 +1251,7 @@ void HStackCheckEliminator::Process() {
         HInstruction* instr = dominator->first();
         while (instr != NULL) {
           if (instr->IsCall()) {
-            RemoveStackCheck(back_edge);
+            block->loop_information()->stack_check()->set_eliminated(true);

[fschneider, 2011/06/22 07:41:18]

Idea for improvement: Can you delete the HStackCheck instruction from the graph
instead of marking it here and eliminating it in the code generator? This would
eliminate the environment uses before doing register allocation and could
potentially help shortening live ranges.

[Søren Thygesen Gjesse, 2011/06/27 11:07:52]

Good point. Changed the elimination to unlink the stack check instruction from
the graph instead of having a boolean flag on it.

             break;
           }
           instr = instr->next();
@@ -1271,18 +1268,6 @@ void HStackCheckEliminator::Process() {
 }
 
 
-void HStackCheckEliminator::RemoveStackCheck(HBasicBlock* block) {
-  HInstruction* instr = block->first();
-  while (instr != NULL) {
-    if (instr->IsGoto()) {
-      HGoto::cast(instr)->set_include_stack_check(false);
-      return;
-    }
-    instr = instr->next();
-  }
-}
-
-
 // Simple sparse set with O(1) add, contains, and clear.
 class SparseSet {
  public:
@@ -2136,8 +2121,8 @@ void TestContext::BuildBranch(HValue* value) {
   HTest* test = new(zone()) HTest(value, empty_true, empty_false);
   builder->current_block()->Finish(test);
 
-  empty_true->Goto(if_true(), false);
-  empty_false->Goto(if_false(), false);
+  empty_true->Goto(if_true());
+  empty_false->Goto(if_false());
   builder->set_current_block(NULL);
 }
 
@@ -2229,7 +2214,7 @@ HGraph* HGraphBuilder::CreateGraph() {
     }
     SetupScope(scope);
     VisitDeclarations(scope->declarations());
-    AddInstruction(new(zone()) HStackCheck());
+    AddInstruction(new(zone()) HStackCheck(HStackCheck::kFunctionEntry));
 
     // Add an edge to the body entry.  This is warty: the graph's start
     // environment will be used by the Lithium translation as the initial
@@ -2567,7 +2552,7 @@ void HGraphBuilder::VisitReturnStatement(ReturnStatement* stmt) {
                       test->if_false());
     } else if (context->IsEffect()) {
       CHECK_ALIVE(VisitForEffect(stmt->expression()));
-      current_block()->Goto(function_return(), false);
+      current_block()->Goto(function_return());
     } else {
       ASSERT(context->IsValue());
       CHECK_ALIVE(VisitForValue(stmt->expression()));
@@ -2758,6 +2743,19 @@ void HGraphBuilder::PreProcessOsrEntry(IterationStatement* statement) {
 }
 
 
+void HGraphBuilder::VisitLoopBody(Statement* body,
+                                  HBasicBlock* loop_entry,
+                                  BreakAndContinueInfo* break_info) {
+  BreakAndContinueScope push(break_info, this);
+  HStackCheck* stack_check =
+      new(zone()) HStackCheck(HStackCheck::kBackwardsBranch);
+  AddInstruction(stack_check);
+  ASSERT(loop_entry->IsLoopHeader());
+  loop_entry->loop_information()->set_stack_check(stack_check);
+  CHECK_BAILOUT(Visit(body));
+}
+
+
 void HGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
@@ -2765,13 +2763,11 @@ void HGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
   ASSERT(current_block() != NULL);
   PreProcessOsrEntry(stmt);
   HBasicBlock* loop_entry = CreateLoopHeaderBlock();
-  current_block()->Goto(loop_entry, false);
+  current_block()->Goto(loop_entry);
   set_current_block(loop_entry);
 
   BreakAndContinueInfo break_info(stmt);
-  { BreakAndContinueScope push(&break_info, this);
-    CHECK_BAILOUT(Visit(stmt->body()));
-  }
+  CHECK_BAILOUT(VisitLoopBody(stmt->body(), loop_entry, &break_info));
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
   HBasicBlock* loop_successor = NULL;
@@ -2809,7 +2805,7 @@ void HGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
   ASSERT(current_block() != NULL);
   PreProcessOsrEntry(stmt);
   HBasicBlock* loop_entry = CreateLoopHeaderBlock();
-  current_block()->Goto(loop_entry, false);
+  current_block()->Goto(loop_entry);
   set_current_block(loop_entry);
 
   // If the condition is constant true, do not generate a branch.
@@ -2832,7 +2828,7 @@ void HGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
   BreakAndContinueInfo break_info(stmt);
   if (current_block() != NULL) {
     BreakAndContinueScope push(&break_info, this);
-    CHECK_BAILOUT(Visit(stmt->body()));
+    CHECK_BAILOUT(VisitLoopBody(stmt->body(), loop_entry, &break_info));
   }
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
@@ -2855,7 +2851,7 @@ void HGraphBuilder::VisitForStatement(ForStatement* stmt) {
   ASSERT(current_block() != NULL);
   PreProcessOsrEntry(stmt);
   HBasicBlock* loop_entry = CreateLoopHeaderBlock();
-  current_block()->Goto(loop_entry, false);
+  current_block()->Goto(loop_entry);
   set_current_block(loop_entry);
 
   HBasicBlock* loop_successor = NULL;
@@ -2877,7 +2873,7 @@ void HGraphBuilder::VisitForStatement(ForStatement* stmt) {
   BreakAndContinueInfo break_info(stmt);
   if (current_block() != NULL) {
     BreakAndContinueScope push(&break_info, this);
-    CHECK_BAILOUT(Visit(stmt->body()));
+    CHECK_BAILOUT(VisitLoopBody(stmt->body(), loop_entry, &break_info));
   }
   HBasicBlock* body_exit =
       JoinContinue(stmt, current_block(), break_info.continue_block());
@@ -4486,7 +4482,7 @@ bool HGraphBuilder::TryInline(Call* expr) {
       ASSERT(function_return() != NULL);
       ASSERT(call_context()->IsEffect() || call_context()->IsValue());
       if (call_context()->IsEffect()) {
-        current_block()->Goto(function_return(), false);
+        current_block()->Goto(function_return());
       } else {
         current_block()->AddLeaveInlined(undefined, function_return());
       }
@@ -4501,8 +4497,8 @@ bool HGraphBuilder::TryInline(Call* expr) {
       HTest* test = new(zone()) HTest(undefined, empty_true, empty_false);
       current_block()->Finish(test);
 
-      empty_true->Goto(inlined_test_context()->if_true(), false);
-      empty_false->Goto(inlined_test_context()->if_false(), false);
+      empty_true->Goto(inlined_test_context()->if_true());
+      empty_false->Goto(inlined_test_context()->if_false());
     }
   }
 
@@ -4519,12 +4515,12 @@ bool HGraphBuilder::TryInline(Call* expr) {
     if (if_true->HasPredecessor()) {
       if_true->SetJoinId(expr->id());
       HBasicBlock* true_target = TestContext::cast(ast_context())->if_true();
-      if_true->Goto(true_target, false);
+      if_true->Goto(true_target);
     }
     if (if_false->HasPredecessor()) {
       if_false->SetJoinId(expr->id());
       HBasicBlock* false_target = TestContext::cast(ast_context())->if_false();
-      if_false->Goto(false_target, false);
+      if_false->Goto(false_target);
     }
     set_current_block(NULL);