1 files changed, 9 insertions, 0 deletions
diff --git a/src/tools/moc/preprocessor.cpp b/src/tools/moc/preprocessor.cpp
index a2a1a958cf..a47896d722 100644
--- a/src/tools/moc/preprocessor.cpp
+++ b/src/tools/moc/preprocessor.cpp
@@ -154,6 +154,11 @@ bool Preprocessor::skipBranch()
 Symbols Preprocessor::tokenize(const QByteArray& input, int lineNum, Preprocessor::TokenizeMode mode)
 {
     Symbols symbols;
+    // Preallocate some space to speed up the code below.
+    // The magic divisor value was found by calculating the average ratio between
+    // input size and the final size of symbols.
+    // This yielded a value of 16.x when compiling Qt Base.
+    symbols.reserve(input.size() / 16);
     const char *begin = input.constData();
     const char *data = begin;
     while (*data) {
@@ -1217,6 +1222,10 @@ Symbols Preprocessor::preprocessed(const QByteArray &filename, QFile *file)
 
     // phase 3: preprocess conditions and substitute macros
     Symbols result;
+    // Preallocate some space to speed up the code below.
+    // The magic value was found by logging the final size
+    // and calculating an average when running moc over FOSS projects.
+    result.reserve(file->size() / 300000);
     preprocess(filename, result);
     mergeStringLiterals(&result);