Include the loop header block when eliminating stack checks

In simple unconditional loops - like the following - the hydrogen stack check elimination did not detect the call as the loop header block itself was not considered.

function f(o) {
  while(true) {
    o.a();
  }
}

R=fschneider@chromium.org

BUG=none
TEST=none

Review URL: http://codereview.chromium.org//7210010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8329 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -1250,16 +1250,20 @@ void HStackCheckEliminator::Process() {
     if (block->IsLoopHeader()) {
       HBasicBlock* back_edge = block->loop_information()->GetLastBackEdge();
       HBasicBlock* dominator = back_edge;
-      bool back_edge_dominated_by_call = false;
-      while (dominator != block && !back_edge_dominated_by_call) {
+      while (true) {
         HInstruction* instr = dominator->first();
-        while (instr != NULL && !back_edge_dominated_by_call) {
+        while (instr != NULL) {
           if (instr->IsCall()) {
             RemoveStackCheck(back_edge);
-            back_edge_dominated_by_call = true;
+            break;
           }
           instr = instr->next();
         }
+
+        // Done when the loop header is processed.
+        if (dominator == block) break;
+
+        // Move up the dominator tree.
         dominator = dominator->dominator();
       }
     }