perf(profiling): do slightly less work when possible (#15025)

## Description

This PR updates a small part of the logic in the Profiler / Stack V2 to
only fetch the `filename_str` if we are going to use it (which may not
be the case if we are pushing a "Task name frame".

## Risks

As far as I can tell, this is a functional no-op as it is effectively
only deferring the declaration (and populating) of a variable –
`filename_str` – to later in the code.

Author: KowalskiThomas

ddtrace/internal/datadog/profiling/stack_v2/src/stack_renderer.cpp

@@ -129,25 +129,17 @@ StackRenderer::render_frame(Frame& frame)
     // some defaults.
     static constexpr std::string_view missing_filename = "<unknown file>";
     static constexpr std::string_view missing_name = "<unknown function>";
-    std::string_view filename_str;
-    std::string_view name_str;
 
-    auto maybe_filename_str = string_table.lookup(frame.filename);
-    if (maybe_filename_str) {
-        filename_str = maybe_filename_str->get();
-    } else {
-        filename_str = missing_filename;
-    }
+    auto line = frame.location.line;
 
+    std::string_view name_str;
     auto maybe_name_str = string_table.lookup(frame.name);
     if (maybe_name_str) {
         name_str = maybe_name_str->get();
     } else {
         name_str = missing_name;
     }
 
-    auto line = frame.location.line;
-
     // DEV: Echion pushes a dummy frame containing task name, and its line
     // number is set to 0.
     if (line == 0) {
@@ -159,6 +151,14 @@ StackRenderer::render_frame(Frame& frame)
         return;
     }
 
+    std::string_view filename_str;
+    auto maybe_filename_str = string_table.lookup(frame.filename);
+    if (maybe_filename_str) {
+        filename_str = maybe_filename_str->get();
+    } else {
+        filename_str = missing_filename;
+    }
+
     ddup_push_frame(sample, name_str, filename_str, 0, line);
 }
 

ddtrace/internal/datadog/profiling/stack_v2/src/stack_v2.cpp

@@ -3,9 +3,6 @@
 #include "sampler.hpp"
 #include "thread_span_links.hpp"
 
-#include <mutex>
-#include <unordered_map>
-
 using namespace Datadog;
 
 static PyObject*

ddtrace/internal/datadog/profiling/stack_v2/src/thread_span_links.cpp

@@ -1,6 +1,5 @@
 #include "thread_span_links.hpp"
 
-#include <iostream>
 #include <mutex>
 #include <optional>
 #include <stdint.h>