Bug 1288778: Add a telemetry probe for usage of asm.js / wasm; r=luke, data-review=bsmedberg

MozReview-Commit-ID: D8yiiobompo

--HG--
extra : rebase_source : 889800ed00a5f05522bd8235491dfd0bee059f9a
extra : amend_source : 268b1d5b811e58d2748f9780992e4769432cb681

js/src/asmjs/WasmBinary.h

@@ -24,6 +24,14 @@
 namespace js {
 namespace wasm {
 
+// Telemetry sample values for the JS_AOT_USAGE key, indicating whether asm.js
+// or WebAssembly is used.
+
+enum class Telemetry {
+    ASMJS = 0,
+    WASM = 1
+};
+
 static const uint32_t MagicNumber        = 0x6d736100; // "\0asm"
 static const uint32_t EncodingVersion    = 0x0b;
 

js/src/asmjs/WasmModule.cpp

@@ -870,5 +870,8 @@ Module::instantiate(JSContext* cx,
         }
     }
 
+    uint32_t mode = uint32_t(metadata().isAsmJS() ? Telemetry::ASMJS : Telemetry::WASM);
+    cx->runtime()->addTelemetry(JS_TELEMETRY_AOT_USAGE, mode);
+
     return true;
 }

js/src/jsfriendapi.h

@@ -133,6 +133,7 @@ enum {
     JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_CONTENT,
     JS_TELEMETRY_DEPRECATED_LANGUAGE_EXTENSIONS_IN_ADDONS,
     JS_TELEMETRY_ADDON_EXCEPTIONS,
+    JS_TELEMETRY_AOT_USAGE,
     JS_TELEMETRY_END
 };
 

js/xpconnect/src/XPCJSRuntime.cpp

@@ -3159,6 +3159,9 @@ AccumulateTelemetryCallback(int id, uint32_t sample, const char* key)
       case JS_TELEMETRY_ADDON_EXCEPTIONS:
         Telemetry::Accumulate(Telemetry::JS_TELEMETRY_ADDON_EXCEPTIONS, nsDependentCString(key), sample);
         break;
+      case JS_TELEMETRY_AOT_USAGE:
+        Telemetry::Accumulate(Telemetry::JS_AOT_USAGE, sample);
+        break;
       default:
         MOZ_ASSERT_UNREACHABLE("Unexpected JS_TELEMETRY id");
     }

toolkit/components/telemetry/Histograms.json

@@ -10299,5 +10299,13 @@
     "keyed": true,
     "n_values": 6,
     "description": "Number of revoke actions on permissions in the control center, keyed by permission id. Values represent the permission type that was revoked. (0=unknown, 1=permanently allowed, 2=permanently blocked, 3=temporarily allowed, 4=temporarily blocked)"
+  },
+  "JS_AOT_USAGE": {
+    "alert_emails": ["luke@mozilla.com", "bbouvier@mozilla.com"],
+    "bug_numbers": [1288778],
+    "expires_in_version": "56",
+    "kind": "enumerated",
+    "n_values": 4,
+    "description": "Counts the number of asm.js vs WebAssembly modules instanciations, at the time modules are getting instanciated."
   }
 }