[gdb] Add gdb macro 'pn' that prints TurboFan nodes

The macro pn ensures that TurboFan nodes can be easily
printed in gdb, even in release builds where Node::Print
is sometimes not available (because all uses have been
inlined).

This CL also modifies the print function to deal gracefully
with nullptr input nodes, which is helpful for debugging.

Change-Id: Ib5f58aa13b719c8390826bc89dfe21cf58586de5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1672941Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62422}

src/compiler/node.cc

@@ -303,7 +303,13 @@ void Node::Print() const {
 void Node::Print(std::ostream& os) const {
   os << *this << std::endl;
   for (Node* input : this->inputs()) {
-    os << "  " << *input << std::endl;
+    os << "  ";
+    if (input) {
+      os << *input;
+    } else {
+      os << "(NULL)";
+    }
+    os << std::endl;
   }
 }
 

src/diagnostics/DEPS

 include_rules = [
   "+components/crash/core/common/crash_key.h",
+  "+src/compiler/node.h",
 ]

src/diagnostics/objects-printer.cc

@@ -50,6 +50,7 @@
 #include "src/objects/js-segment-iterator-inl.h"
 #include "src/objects/js-segmenter-inl.h"
 #endif  // V8_INTL_SUPPORT
+#include "src/compiler/node.h"
 #include "src/objects/js-weak-refs-inl.h"
 #include "src/objects/literal-objects-inl.h"
 #include "src/objects/microtask-inl.h"
@@ -2829,3 +2830,7 @@ V8_EXPORT_PRIVATE extern void _v8_internal_Print_TransitionTree(void* object) {
 #endif
   }
 }
+
+V8_EXPORT_PRIVATE extern void _v8_internal_Node_Print(void* object) {
+  reinterpret_cast<i::compiler::Node*>(object)->Print();
+}

tools/gdbinit

@@ -65,6 +65,15 @@ Print the current JavaScript stack trace
 Usage: jst
 end
 
+# Print TurboFan graph node.
+define pn
+call _v8_internal_Node_Print((void*)($arg0))
+end
+document pn
+Print a v8 TurboFan graph node
+Usage: pn node_address
+end
+
 # Skip the JavaScript stack.
 define jss
 set $js_entry_sp=v8::internal::Isolate::Current()->thread_local_top()->js_entry_sp_