Add --print-flow-graph-filter to allow filtering debugging output.

runtime/vm/il_printer.cc

Index: runtime/vm/il_printer.cc
diff --git a/runtime/vm/il_printer.cc b/runtime/vm/il_printer.cc
index c81ac93ec1280d8a67eaba9f26d150cd7e2065d3..6889e3cb496dc88da977fde8bdba5d7d9d73c2c6 100644
--- a/runtime/vm/il_printer.cc
+++ b/runtime/vm/il_printer.cc
@@ -12,7 +12,8 @@
 namespace dart {
 
 DEFINE_FLAG(bool, print_environments, false, "Print SSA environments.");
-
+DEFINE_FLAG(charp, print_flow_graph_filter, NULL,
+    "Print only IR of functions with matching names");
 
 void BufferFormatter::Print(const char* format, ...) {
   va_list args;
@@ -33,6 +34,52 @@ void BufferFormatter::VPrint(const char* format, va_list args) {
 }
 
 
+// Checks whether function's name matches the given filter, which is
+// a comma-separated list of strings.
+bool FlowGraphPrinter::PassesFilter(const char* filter,
+                                    const Function& function) {
+  if (filter == NULL) {
+    return true;
+  }
+
+  char* save_ptr;  // Needed for strtok_r.
+  const char* function_name = function.ToFullyQualifiedCString();
+  intptr_t function_name_len = strlen(function_name);
+
+  intptr_t len = strlen(filter) + 1;  // Length with \0.
+  char* filter_buffer = new char[len];
+  strncpy(filter_buffer, filter, len);  // strtok modifies arg 1.
+  char* token = strtok_r(filter_buffer, ",", &save_ptr);
+  bool found = false;
+  while (token != NULL) {
+    if (strstr(function_name, token) != NULL) {
+      found = true;
+      break;
+    }
+    const intptr_t token_len = strlen(token);
+    if (token[token_len - 1] == '%') {
+      if (function_name_len > token_len) {
+        const char* suffix = function_name +
+            (function_name_len - token_len + 1);
+        if (strncmp(suffix, token, token_len - 1) == 0) {
+          found = true;
+          break;
+        }
+      }
+    }
+    token = strtok_r(NULL, ",", &save_ptr);
+  }
+  delete[] filter_buffer;
+
+  return found;
+}
+
+
+bool FlowGraphPrinter::ShouldPrint(const Function& function) {
+  return PassesFilter(FLAG_print_flow_graph_filter, function);
+}
+
+
 void FlowGraphPrinter::PrintGraph(const char* phase, FlowGraph* flow_graph) {
   OS::Print("*** BEGIN CFG\n%s\n", phase);
   FlowGraphPrinter printer(*flow_graph);