moc: Cache header lookups to reduce number of file stat's

This improves moc performance on Windows where file-stat'ing is slow
and where the number of project include paths to search is often high
because project third-party headers are installed in separate
directories rather than a shared include path such as /usr/include.

In a real project of non-trivial size it reduces the total
from-scratch build time of an optimized build using CMake+ninja with
32 cores by 11% from ~11m35s to ~10m15s.

Change-Id: Ieed59646927ed75c55ed9efa97600c328b2fed2c
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

2 files changed, 22 insertions, 8 deletions

diff --git a/src/tools/moc/preprocessor.cpp b/src/tools/moc/preprocessor.cpp
index 11bf8d7937..f5639ffe31 100644
--- a/src/tools/moc/preprocessor.cpp
+++ b/src/tools/moc/preprocessor.cpp
@@ -1005,22 +1005,20 @@ static void mergeStringLiterals(Symbols *_symbols)
     }
 }
 
-QByteArray Preprocessor::resolveInclude(const QByteArray &include, const QByteArray &relativeTo)
+static QByteArray searchIncludePaths(const QList<Parser::IncludePath> &includepaths,
+                                     const QByteArray &include)
 {
-    // #### stringery
     QFileInfo fi;
-    if (!relativeTo.isEmpty())
-        fi.setFile(QFileInfo(QString::fromLocal8Bit(relativeTo.constData())).dir(), QString::fromLocal8Bit(include.constData()));
-    for (int j = 0; j < Preprocessor::includes.size() && !fi.exists(); ++j) {
-        const IncludePath &p = Preprocessor::includes.at(j);
+    for (int j = 0; j < includepaths.size() && !fi.exists(); ++j) {
+        const Parser::IncludePath &p = includepaths.at(j);
         if (p.isFrameworkPath) {
             const int slashPos = include.indexOf('/');
             if (slashPos == -1)
                 continue;
             fi.setFile(QString::fromLocal8Bit(p.path + '/' + include.left(slashPos) + ".framework/Headers/"),
-                       QString::fromLocal8Bit(include.mid(slashPos + 1).constData()));
+                       QString::fromLocal8Bit(include.mid(slashPos + 1)));
         } else {
-            fi.setFile(QString::fromLocal8Bit(p.path.constData()), QString::fromLocal8Bit(include.constData()));
+            fi.setFile(QString::fromLocal8Bit(p.path), QString::fromLocal8Bit(include));
         }
         // try again, maybe there's a file later in the include paths with the same name
         // (186067)
@@ -1035,6 +1033,21 @@ QByteArray Preprocessor::resolveInclude(const QByteArray &include, const QByteAr
     return fi.canonicalFilePath().toLocal8Bit();
 }
 
+QByteArray Preprocessor::resolveInclude(const QByteArray &include, const QByteArray &relativeTo)
+{
+    if (!relativeTo.isEmpty()) {
+        QFileInfo fi;
+        fi.setFile(QFileInfo(QString::fromLocal8Bit(relativeTo)).dir(), QString::fromLocal8Bit(include));
+        if (fi.exists() && !fi.isDir())
+            return fi.canonicalFilePath().toLocal8Bit();
+    }
+
+    auto it = nonlocalIncludePathResolutionCache.find(include);
+    if (it == nonlocalIncludePathResolutionCache.end())
+       it = nonlocalIncludePathResolutionCache.insert(include, searchIncludePaths(includes, include));
+    return it.value();
+}
+
 void Preprocessor::preprocess(const QByteArray &filename, Symbols &preprocessed)
 {
     currentFilenames.push(filename);
diff --git a/src/tools/moc/preprocessor.h b/src/tools/moc/preprocessor.h
index a7eb1a19e1..39f56d6e92 100644
--- a/src/tools/moc/preprocessor.h
+++ b/src/tools/moc/preprocessor.h
@@ -61,6 +61,7 @@ public:
     static bool preprocessOnly;
     QList<QByteArray> frameworks;
     QSet<QByteArray> preprocessedIncludes;
+    QHash<QByteArray, QByteArray> nonlocalIncludePathResolutionCache;
     Macros macros;
     QByteArray resolveInclude(const QByteArray &filename, const QByteArray &relativeTo);
     Symbols preprocessed(const QByteArray &filename, QFile *device);