Enable precompiled headers on iOS, tvOS, watchOS

The actual blocker for precompiled headers is not the iOS/tvOS/watchOS
platforms, but the way qmake handled multiple-architecture builds on
Apple platforms.

This patch allows multi-arch builds to be performed while using
precompiled headers.

Since df91ef3d6c55692a0236f67b6c6b134a3bf84098 (April 2009), Clang has
had support for PCH files in the driver, which allows to use the
-include flag to automatically translate to -include-pch. We can then
take advantage of the fact that the -include option is allowed to not
be separate from its argument, which lets us take advantage of -Xarch to
specify a per-architecture precompiled header file.

This is done through some magic in the qmake Makefile generator which
"multiplexes" the PCH creation rule across multiple architectures and
replaces a series of tokens with the proper precompiled header paths
and architecture flags at usage point.

Change-Id: I76c8dc9cda7e218869c2919f023d9b04f311c6fd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 23 insertions, 3 deletions

diff --git a/qmake/generators/unix/unixmake.cpp b/qmake/generators/unix/unixmake.cpp
index b0f7593fbe..349dcd2f40 100644
--- a/qmake/generators/unix/unixmake.cpp
+++ b/qmake/generators/unix/unixmake.cpp
@@ -194,6 +194,18 @@ UnixMakefileGenerator::init()
                 if (!language.isEmpty()) {
                     pchFlags.replace(QLatin1String("${QMAKE_PCH_OUTPUT}"),
                                      escapeFilePath(pchBaseName + language + headerSuffix));
+                    const ProStringList pchArchs = project->values("QMAKE_PCH_ARCHS");
+                    for (const ProString &arch : pchArchs) {
+                        QString suffix = headerSuffix;
+                        suffix.replace(QLatin1String("${QMAKE_PCH_ARCH}"), arch.toQString());
+                        if (project->isActiveConfig("clang_pch_style")
+                            && (suffix.endsWith(QLatin1String(".pch"))
+                                || suffix.endsWith(QLatin1String(".gch")))) {
+                            suffix.chop(4); // must omit header suffix for -include to recognize the PCH
+                        }
+                        pchFlags.replace(QLatin1String("${QMAKE_PCH_OUTPUT_") + arch + QLatin1Char('}'),
+                                         escapeFilePath(pchBaseName + language + suffix));
+                    }
                 }
             }
 
@@ -351,9 +363,17 @@ QStringList
                     if (!file.endsWith(extension.toQString()))
                         continue;
 
-                    QString precompiledHeader = header_prefix + language + header_suffix;
-                    if (!ret.contains(precompiledHeader))
-                        ret += precompiledHeader;
+                    ProStringList pchArchs = project->values("QMAKE_PCH_ARCHS");
+                    if (pchArchs.isEmpty())
+                        pchArchs << ProString(); // normal single-arch PCH
+                    for (const ProString &arch : qAsConst(pchArchs)) {
+                        QString suffix = header_suffix;
+                        if (!arch.isEmpty())
+                            suffix.replace(QLatin1String("${QMAKE_PCH_ARCH}"), arch.toQString());
+                        QString precompiledHeader = header_prefix + language + suffix;
+                        if (!ret.contains(precompiledHeader))
+                            ret += precompiledHeader;
+                    }
 
                     goto foundPrecompiledDependency;
                 }