Introduce qmake feature use_gold_linker

This patch adds the feature use_gold_linker to use the gold linker that
has been part of of GNU binutils since 2008. Gold links C++ libraries
much faster and use less memory.

The feature is autodetected when building Qt on Linux, but can be disabled
in configure. On MingW builds it is default off but can be enabled for
cross builds.

Change-Id: Icdd6ba2e706b2c791bcf44b6e718c2b7a5eb2218
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

configure

@@ -698,6 +698,7 @@ CFG_INOTIFY=auto
 CFG_EVENTFD=auto
 CFG_RPATH=yes
 CFG_FRAMEWORK=auto
+CFG_USE_GOLD_LINKER=auto
 DEFINES=
 INCLUDES=
 D_FLAGS=
@@ -1592,6 +1593,13 @@ while [ "$#" -gt 0 ]; do
             UNKNOWN_OPT=yes
         fi
         ;;
+    use-gold-linker)
+        if [ "$VAL" = "yes" ] || [ "$VAL" = "no" ]; then
+            CFG_USE_GOLD_LINKER="$VAL"
+        else
+            UNKNOWN_OPT=yes
+        fi
+        ;;
     zlib)
         [ "$VAL" = "qt" ] && VAL=yes
         if [ "$VAL" = "yes" ] || [ "$VAL" = "no" ] || [ "$VAL" = "system" ]; then
@@ -2465,6 +2473,9 @@ Additional options:
                               linker optimizations (Qt/X11 and Qt for Embedded Linux only;
                               experimental; needs GNU ld >= 2.18).
 
+    -no-use-gold-linker ..... Do not link using the GNU gold linker.
+ +  -use-gold-linker ........ Link using the GNU gold linker if available.
+
     -force-asserts ........ Force Q_ASSERT to be enabled even in release builds.
 
     -device <name> ............... Cross-compile for device <name> (experimental)
@@ -3230,6 +3241,19 @@ if [ "$CFG_REDUCE_EXPORTS" != "no" ]; then
     fi
 fi
 
+# auto-detect -fuse-ld=gold support
+if [ "$CFG_USE_GOLD_LINKER" != "no" ]; then
+    if linkerSupportsFlag $TEST_COMPILER -fuse-ld=gold; then
+       CFG_USE_GOLD_LINKER=yes
+    else
+        if [ "$CFG_USE_GOLD_LINKER" = "yes" ]; then
+            echo "-use-gold-linker was requested but this compiler does not support it"
+            exit 1
+        fi
+        CFG_USE_GOLD_LINKER=no
+    fi
+fi
+
 # auto-detect -fstack-protector-strong support (for QNX only currently)
 if [ "$XPLATFORM_QNX" = "yes" ]; then
     if compilerSupportsFlag $TEST_COMPILER -fstack-protector-strong; then
@@ -5598,6 +5622,7 @@ fi
 [ "$CFG_REDUCE_RELOCATIONS" = "yes" ] && QT_CONFIG="$QT_CONFIG reduce_relocations"
 [ "$CFG_STRIP" = "no" ] && QMAKE_CONFIG="$QMAKE_CONFIG nostrip"
 [ "$CFG_PRECOMPILE" = "yes" ] && QMAKE_CONFIG="$QMAKE_CONFIG precompile_header"
+[ "$CFG_USE_GOLD_LINKER" = "yes" ] && QMAKE_CONFIG="$QMAKE_CONFIG use_gold_linker"
 if [ "$CFG_SEPARATE_DEBUG_INFO" = "yes" ]; then
     QT_CONFIG="$QT_CONFIG separate_debug_info"
 fi
@@ -6472,6 +6497,7 @@ else
 fi
 unset build_mode release
 echo "  Using C++11 ............ $CFG_CXX11"
+echo "  Using gold linker....... $CFG_USE_GOLD_LINKER"
 echo "  Using PCH .............. $CFG_PRECOMPILE"
 echo "  Target compiler supports:"
 if [ "$CFG_ARCH" = "i386" -o "$CFG_ARCH" = "x86_64" ]; then

mkspecs/common/gcc-base-unix.conf

@@ -16,6 +16,7 @@ QMAKE_LFLAGS_SONAME    += -Wl,-soname,
 QMAKE_LFLAGS_THREAD    +=
 QMAKE_LFLAGS_RPATH      = -Wl,-rpath,
 QMAKE_LFLAGS_RPATHLINK  = -Wl,-rpath-link,
+QMAKE_LFLAGS_USE_GOLD   = -fuse-ld=gold
 
 # -Bsymbolic-functions (ld) support
 QMAKE_LFLAGS_BSYMBOLIC_FUNC = -Wl,-Bsymbolic-functions

mkspecs/features/default_post.prf

@@ -61,6 +61,8 @@ debug {
     QMAKE_LIBFLAGS += $$QMAKE_LIBFLAGS_RELEASE
 }
 
+use_gold_linker: QMAKE_LFLAGS += $$QMAKE_LFLAGS_USE_GOLD
+
 dll:win32: QMAKE_LFLAGS += $$QMAKE_LFLAGS_DLL
 static:mac: QMAKE_LFLAGS += $$QMAKE_LFLAGS_STATIC_LIB
 staticlib:unix {

mkspecs/win32-g++/qmake.conf

@@ -78,6 +78,7 @@ QMAKE_LFLAGS_WINDOWS    = -Wl,-subsystem,windows
 QMAKE_LFLAGS_DLL        = -shared
 QMAKE_LFLAGS_CXX11      =
 QMAKE_LFLAGS_GCSECTIONS = -Wl,--gc-sections
+QMAKE_LFLAGS_USE_GOLD   = -fuse-ld=gold
 QMAKE_LINK_OBJECT_MAX   = 10
 QMAKE_LINK_OBJECT_SCRIPT = object_script
 QMAKE_PREFIX_STATICLIB  = lib

tools/configure/configureapp.cpp

@@ -250,6 +250,8 @@ Configure::Configure(int& argc, char** argv)
 
     dictionary[ "C++11" ]           = "auto";
 
+    dictionary[ "USE_GOLD_LINKER" ] = "no";
+
     dictionary[ "SHARED" ]          = "yes";
 
     dictionary[ "ZLIB" ]            = "auto";
@@ -461,6 +463,10 @@ void Configure::parseCmdLine()
             dictionary[ "C++11" ] = "yes";
         else if (configCmdLine.at(i) == "-no-c++11")
             dictionary[ "C++11" ] = "no";
+        else if (configCmdLine.at(i) == "-use-gold-linker")
+            dictionary[ "USE_GOLD_LINKER" ] = "yes";
+        else if (configCmdLine.at(i) == "-no-use-gold-linker")
+            dictionary[ "USE_GOLD_LINKER" ] = "no";
         else if (configCmdLine.at(i) == "-shared")
             dictionary[ "SHARED" ] = "yes";
         else if (configCmdLine.at(i) == "-static")
@@ -1762,6 +1768,9 @@ bool Configure::displayHelp()
         desc("C++11", "yes", "-c++11",                  "Compile Qt with C++11 support enabled.");
         desc("C++11", "no", "-no-c++11",                "Do not compile Qt with C++11 support enabled.\n");
 
+        desc("USE_GOLD_LINKER", "yes", "-use-gold-linker",                  "Link using the GNU gold linker (gcc only).");
+        desc("USE_GOLD_LINKER", "no", "-no-use-gold-linker",                "Do not link using the GNU gold linker.\n");
+
         desc("SHARED", "yes",   "-shared",              "Create and use shared Qt libraries.");
         desc("SHARED", "no",    "-static",              "Create and use static Qt libraries.\n");
 
@@ -2609,6 +2618,9 @@ void Configure::generateOutputVars()
     if (dictionary[ "C++11" ] == "yes")
         qtConfig += "c++11";
 
+    if (dictionary[ "USE_GOLD_LINKER" ] == "yes")
+        qmakeConfig += "use_gold_linker";
+
     if (dictionary[ "SHARED" ] == "no")
         qtConfig += "static";
     else