[maglev] Show dead bytecodes when building the graph

Bug: v8:7700
Change-Id: I3da7bbd928e0a587b4eb2c90c86f71405da67323
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3876378
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83042}

src/maglev/maglev-graph-builder.h

@@ -167,6 +167,13 @@ class MaglevGraphBuilder {
 
   void MarkBytecodeDead() {
     DCHECK_NULL(current_block_);
+    if (FLAG_trace_maglev_graph_building) {
+      std::cout << "== Dead ==\n"
+                << std::setw(4) << iterator_.current_offset() << " : ";
+      interpreter::BytecodeDecoder::Decode(std::cout,
+                                           iterator_.current_address());
+      std::cout << std::endl;
+    }
 
     // If the current bytecode is a jump to elsewhere, then this jump is
     // also dead and we should make sure to merge it as a dead predecessor.