[turbofan] Ensure AstGraphBuilder::CheckOsrEntry hits once.

The predicate in question should only trigger once and hence the stack
height should not be updated incrementally. This puts checks into place
ensuring this holds.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2333923008
Cr-Commit-Position: refs/heads/master@{#39472}

src/compilation-info.cc

@@ -79,7 +79,7 @@ CompilationInfo::CompilationInfo(ParseInfo* parse_info,
                        isolate->is_profiling()),
       parameter_count_(0),
       optimization_id_(-1),
-      osr_expr_stack_height_(0),
+      osr_expr_stack_height_(-1),
       debug_name_(debug_name) {}
 
 CompilationInfo::~CompilationInfo() {

src/compiler/ast-graph-builder.cc

@@ -3988,8 +3988,8 @@ Node* AstGraphBuilder::TryFastToName(Node* input) {
 
 bool AstGraphBuilder::CheckOsrEntry(IterationStatement* stmt) {
   if (info()->osr_ast_id() == stmt->OsrEntryId()) {
-    info()->set_osr_expr_stack_height(std::max(
-        environment()->stack_height(), info()->osr_expr_stack_height()));
+    DCHECK_EQ(-1, info()->osr_expr_stack_height());
+    info()->set_osr_expr_stack_height(environment()->stack_height());
     return true;
   }
   return false;