Bug 1500692 - Add an AUTO_PROFILER_LABEL_CATEGORY_PAIR macro. r=njn

This is similar to AUTO_PROFILER_LABEL, but with only one argument: a category pair.
This reduces duplication for label frames that want just the subcategory name as
their label: Instead of AUTO_PROFILER_LABEL("Layer building", GRAPHICS_LayerBuilding),
you can now just write AUTO_PROFILER_LABEL_CATEGORY_PAIR(GRAPHICS_LayerBuilding) and
the string will automatically be taken from the subcategory.

Differential Revision: https://phabricator.services.mozilla.com/D11339

--HG--
extra : moz-landing-system : lando

js/public/ProfilingStack.h

@@ -157,7 +157,7 @@ class ProfilingStackFrame {
                   mozilla::recordreplay::Behavior::DontPreserve>
       pcOffsetIfJS_;
 
-  // Bits 0...7 hold the Flags. Bits 8...31 hold the category pair.
+  // Bits 0...8 hold the Flags. Bits 9...31 hold the category pair.
   mozilla::Atomic<uint32_t, mozilla::ReleaseAcquire,
                   mozilla::recordreplay::Behavior::DontPreserve>
       flagsAndCategoryPair_;
@@ -178,8 +178,8 @@ class ProfilingStackFrame {
     return *this;
   }
 
-  // 8 bits for the flags.
-  // That leaves 32 - 8 = 25 bits for the category pair.
+  // 9 bits for the flags.
+  // That leaves 32 - 9 = 23 bits for the category pair.
   enum class Flags : uint32_t {
     // The first three flags describe the kind of the frame and are
     // mutually exclusive. (We still give them individual bits for
@@ -217,7 +217,11 @@ class ProfilingStackFrame {
     // tree view.
     RELEVANT_FOR_JS = 1 << 7,
 
-    FLAGS_BITCOUNT = 8,
+    // If set, causes the label on this ProfilingStackFrame to be ignored
+    // and to be replaced by the subcategory's label.
+    LABEL_DETERMINED_BY_CATEGORY_PAIR = 1 << 8,
+
+    FLAGS_BITCOUNT = 9,
     FLAGS_MASK = (1 << FLAGS_BITCOUNT) - 1
   };
 
@@ -254,8 +258,16 @@ class ProfilingStackFrame {
     }
   }
 
-  void setLabel(const char* aLabel) { label_ = aLabel; }
-  const char* label() const { return label_; }
+  const char* label() const {
+    uint32_t flagsAndCategoryPair = flagsAndCategoryPair_;
+    if (flagsAndCategoryPair &
+        uint32_t(Flags::LABEL_DETERMINED_BY_CATEGORY_PAIR)) {
+      auto categoryPair = JS::ProfilingCategoryPair(
+          flagsAndCategoryPair >> uint32_t(Flags::FLAGS_BITCOUNT));
+      return JS::GetProfilingCategoryPairInfo(categoryPair).mLabel;
+    }
+    return label_;
+  }
 
   const char* dynamicString() const { return dynamicString_; }
 

tools/profiler/public/GeckoProfiler.h

@@ -42,6 +42,7 @@
 #  define PROFILER_CLEAR_JS_CONTEXT()
 
 #  define AUTO_PROFILER_LABEL(label, categoryPair)
+#  define AUTO_PROFILER_LABEL_CATEGORY_PAIR(categoryPair)
 #  define AUTO_PROFILER_LABEL_DYNAMIC_CSTR(label, categoryPair, cStr)
 #  define AUTO_PROFILER_LABEL_DYNAMIC_NSCSTRING(label, categoryPair, nsCStr)
 #  define AUTO_PROFILER_LABEL_DYNAMIC_LOSSY_NSSTRING(label, categoryPair, nsStr)
@@ -522,6 +523,16 @@ mozilla::Maybe<ProfilerBufferInfo> profiler_get_buffer_info();
     mozilla::AutoProfilerLabel PROFILER_RAII(      \
         label, nullptr, JS::ProfilingCategoryPair::categoryPair)
 
+// Similar to AUTO_PROFILER_LABEL, but with only one argument: the category
+// pair. The label string is taken from the category pair. This is convenient
+// for labels like AUTO_PROFILER_LABEL_CATEGORY_PAIR(GRAPHICS_LayerBuilding)
+// which would otherwise just repeat the string.
+#  define AUTO_PROFILER_LABEL_CATEGORY_PAIR(categoryPair)     \
+    mozilla::AutoProfilerLabel PROFILER_RAII(                 \
+        "", nullptr, JS::ProfilingCategoryPair::categoryPair, \
+        uint32_t(js::ProfilingStackFrame::Flags::             \
+                     LABEL_DETERMINED_BY_CATEGORY_PAIR))
+
 // Similar to AUTO_PROFILER_LABEL, but with an additional string. The inserted
 // RAII object stores the cStr pointer in a field; it does not copy the string.
 //