Bug 1499507 - Use AppendPrintf to concatenate the label with the dynamic string. r=njn

This code is run during JSON serialization so performance is not a big concern.

Depends on D9195

Differential Revision: https://phabricator.services.mozilla.com/D9197

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

tools/profiler/core/ProfileBufferEntry.cpp

@@ -949,7 +949,7 @@ ProfileBuffer::StreamSamplesToJSON(SpliceableJSONWriter& aWriter, int aThreadId,
                                    double aSinceTime,
                                    UniqueStacks& aUniqueStacks) const
 {
-  UniquePtr<char[]> strbuf = MakeUnique<char[]>(kMaxFrameKeyLength);
+  UniquePtr<char[]> dynStrBuf = MakeUnique<char[]>(kMaxFrameKeyLength);
 
   EntryGetter e(*this);
 
@@ -1024,30 +1024,20 @@ ProfileBuffer::StreamSamplesToJSON(SpliceableJSONWriter& aWriter, int aThreadId,
       } else if (e.Get().IsLabel()) {
         numFrames++;
 
-        // Copy the label into strbuf.
         const char* label = e.Get().u.mString;
-        strncpy(strbuf.get(), label, kMaxFrameKeyLength);
-        size_t i = strlen(label);
+
         e.Next();
 
-        bool seenFirstDynamicStringFragment = false;
+        // Copy potential dynamic string fragments into dynStrBuf, so that
+        // dynStrBuf will then contain the entire dynamic string.
+        size_t i = 0;
+        dynStrBuf[0] = '\0';
         while (e.Has()) {
           if (e.Get().IsDynamicStringFragment()) {
-            // If this is the first dynamic string fragment and we have a
-            // non-empty label, insert a ' ' after the label and before the
-            // dynamic string.
-            if (!seenFirstDynamicStringFragment) {
-              if (i > 0 && i < kMaxFrameKeyLength) {
-                strbuf[i] = ' ';
-                i++;
-              }
-              seenFirstDynamicStringFragment = true;
-            }
-
             for (size_t j = 0; j < ProfileBufferEntry::kNumChars; j++) {
               const char* chars = e.Get().u.mChars;
               if (i < kMaxFrameKeyLength) {
-                strbuf[i] = chars[j];
+                dynStrBuf[i] = chars[j];
                 i++;
               }
             }
@@ -1056,7 +1046,15 @@ ProfileBuffer::StreamSamplesToJSON(SpliceableJSONWriter& aWriter, int aThreadId,
             break;
           }
         }
-        strbuf[kMaxFrameKeyLength - 1] = '\0';
+        dynStrBuf[kMaxFrameKeyLength - 1] = '\0';
+        bool hasDynamicString = (i != 0);
+
+        nsCString frameLabel;
+        if (label[0] != '\0' && hasDynamicString) {
+          frameLabel.AppendPrintf("%s %s", label, dynStrBuf.get());
+        } else {
+          frameLabel.Append(label);
+        }
 
         Maybe<unsigned> line;
         if (e.Has() && e.Get().IsLineNumber()) {
@@ -1077,7 +1075,8 @@ ProfileBuffer::StreamSamplesToJSON(SpliceableJSONWriter& aWriter, int aThreadId,
         }
 
         stack = aUniqueStacks.AppendFrame(
-          stack, UniqueStacks::FrameKey(strbuf.get(), line, column, category));
+          stack, UniqueStacks::FrameKey(std::move(frameLabel), line, column,
+                                        category));
 
       } else if (e.Get().IsJitReturnAddr()) {
         numFrames++;

tools/profiler/core/ProfileBufferEntry.h

@@ -235,10 +235,10 @@ public:
     {
     }
 
-    FrameKey(const char* aLocation, const mozilla::Maybe<unsigned>& aLine,
+    FrameKey(nsCString&& aLocation, const mozilla::Maybe<unsigned>& aLine,
              const mozilla::Maybe<unsigned>& aColumn,
              const mozilla::Maybe<unsigned>& aCategory)
-      : mData(NormalFrameData{ nsCString(aLocation), aLine, aColumn, aCategory })
+      : mData(NormalFrameData{ aLocation, aLine, aColumn, aCategory })
     {
     }