Disable precompiled headers for small modules

Creating a precompiled header exclusively for a one- or two-file module
is wasteful. The time that it takes to build the precompiled source is
on the same order as a regular compilation, so enabling precompiled
headers for those modules just makes the build slower.

Also make it possible to override the precompiled header by just setting
PRECOMPILED_HEADER to empty.

Change-Id: I0e1a09998253489388abfffd14b5f221288c4826
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

10 files changed, 11 insertions, 14 deletions

diff --git a/mkspecs/features/qt_module_headers.prf b/mkspecs/features/qt_module_headers.prf
index 648723d6ff..c77db2193b 100644
--- a/mkspecs/features/qt_module_headers.prf
+++ b/mkspecs/features/qt_module_headers.prf
@@ -157,12 +157,18 @@ MODULE_MASTER_DEPS_HEADER = $$MODULE_BASE_OUTDIR/include/$$MODULE_INCNAME/$${MOD
 }
 SYNCQT.HEADER_FILES += $$MODULE_MASTER_DEPS_HEADER
 
-# Automatically enable precompiled headers for Qt modules,
-# except for Gcc/Windows: Larger precompiled headers crash cc1plus.exe
-# (e.g. with i686-4.8.2-release-posix-dwarf-rt_v3-rev3)
-!if(gcc:equals(QMAKE_HOST.os, Windows)):!equals(TEMPLATE, aux) {
-    isEmpty(PRECOMPILED_HEADER): PRECOMPILED_HEADER = $$MODULE_MASTER_DEPS_HEADER
+# Automatically enable precompiled headers for Qt modules with more than 2 sources
+combined_SOURCES = $$SOURCES $$OBJECTIVE_SOURCES
+count(combined_SOURCES, 2, >) {
+    # except for Gcc/Windows: Larger precompiled headers crash cc1plus.exe
+    # (e.g. with i686-4.8.2-release-posix-dwarf-rt_v3-rev3)
+    !if(gcc:equals(QMAKE_HOST.os, Windows)):!equals(TEMPLATE, aux) {
+        !defined(PRECOMPILED_HEADER, "var"): PRECOMPILED_HEADER = $$MODULE_MASTER_DEPS_HEADER
+    }
+} else {
+    CONFIG -= precompile_header
 }
+unset(combined_SOURCES)
 
 headersclean:!internal_module {
     # Make sure that the header compiles with our strict options
diff --git a/src/platformsupport/accessibility/accessibility.pro b/src/platformsupport/accessibility/accessibility.pro
index 5004dc8cbe..1806d75630 100644
--- a/src/platformsupport/accessibility/accessibility.pro
+++ b/src/platformsupport/accessibility/accessibility.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS += \
     qaccessiblebridgeutils_p.h
diff --git a/src/platformsupport/cglconvenience/cglconvenience.pro b/src/platformsupport/cglconvenience/cglconvenience.pro
index 0422a844aa..89d1fc4643 100644
--- a/src/platformsupport/cglconvenience/cglconvenience.pro
+++ b/src/platformsupport/cglconvenience/cglconvenience.pro
@@ -5,7 +5,6 @@ QT = core-private gui
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS += \
     cglconvenience_p.h
diff --git a/src/platformsupport/clipboard/clipboard.pro b/src/platformsupport/clipboard/clipboard.pro
index 336d81fe46..def2a061a0 100644
--- a/src/platformsupport/clipboard/clipboard.pro
+++ b/src/platformsupport/clipboard/clipboard.pro
@@ -5,7 +5,6 @@ QT = core-private gui
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS += qmacmime_p.h
 SOURCES += qmacmime.mm
diff --git a/src/platformsupport/devicediscovery/devicediscovery.pro b/src/platformsupport/devicediscovery/devicediscovery.pro
index b429b8b97e..881ec4d41e 100644
--- a/src/platformsupport/devicediscovery/devicediscovery.pro
+++ b/src/platformsupport/devicediscovery/devicediscovery.pro
@@ -6,7 +6,6 @@ QT_FOR_CONFIG += gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS += qdevicediscovery_p.h
 
diff --git a/src/platformsupport/glxconvenience/glxconvenience.pro b/src/platformsupport/glxconvenience/glxconvenience.pro
index 41c96d8f0d..58fa9fc479 100644
--- a/src/platformsupport/glxconvenience/glxconvenience.pro
+++ b/src/platformsupport/glxconvenience/glxconvenience.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 LIBS_PRIVATE += $$QMAKE_LIBS_X11
 
diff --git a/src/platformsupport/graphics/graphics.pro b/src/platformsupport/graphics/graphics.pro
index 878fca7f49..9886ee0332 100644
--- a/src/platformsupport/graphics/graphics.pro
+++ b/src/platformsupport/graphics/graphics.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS += $$PWD/qrasterbackingstore_p.h
 SOURCES += $$PWD/qrasterbackingstore.cpp
diff --git a/src/platformsupport/kmsconvenience/kmsconvenience.pro b/src/platformsupport/kmsconvenience/kmsconvenience.pro
index d0ff0d4efb..5ea2e3f208 100644
--- a/src/platformsupport/kmsconvenience/kmsconvenience.pro
+++ b/src/platformsupport/kmsconvenience/kmsconvenience.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 HEADERS +=
     qkmsdevice_p.h
diff --git a/src/platformsupport/platformcompositor/platformcompositor.pro b/src/platformsupport/platformcompositor/platformcompositor.pro
index 633e71fb9d..81c31571d0 100644
--- a/src/platformsupport/platformcompositor/platformcompositor.pro
+++ b/src/platformsupport/platformcompositor/platformcompositor.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 SOURCES += \
     qopenglcompositor.cpp \
diff --git a/src/platformsupport/themes/themes.pro b/src/platformsupport/themes/themes.pro
index 2aeb1f89ad..aeed4d2f47 100644
--- a/src/platformsupport/themes/themes.pro
+++ b/src/platformsupport/themes/themes.pro
@@ -5,7 +5,6 @@ QT = core-private gui-private
 CONFIG += static internal_module
 
 DEFINES += QT_NO_CAST_FROM_ASCII
-PRECOMPILED_HEADER = ../../corelib/global/qt_pch.h
 
 unix:!darwin: \
     include($$PWD/genericunix/genericunix.pri)