Add configure flag to optimize Qt for size

Adds default off configure flag to use compiler optimizations
for size instead of the default speed/size trade-off.

Change-Id: I36702064ef2cc743d2d03a386adf5cefd5371b6e
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

config_help.txt

@@ -83,6 +83,7 @@ Build options:
                          debugging turned on [yes] (Apple and Windows only)
   -optimize-debug ...... Enable debug-friendly optimizations in debug builds
                          [auto] (Not supported with MSVC)
+  -optimize-size ....... Optimize release builds for size instead of speed [no]
   -optimized-tools ..... Build optimized host tools even in debug build [no]
   -force-debug-info .... Create symbol files for release builds [no]
   -separate-debug-info . Split off debug information to separate files [no]

configure.json

@@ -93,6 +93,7 @@
             "nomake": { "type": "addString", "values": [ "examples", "tests", "tools" ] },
             "opensource": { "type": "void", "name": "commercial", "value": "no" },
             "optimize-debug": { "type": "boolean", "name": "optimize_debug" },
+            "optimize-size": { "type": "boolean", "name": "optimize_size" },
             "optimized-qmake": { "type": "boolean", "name": "release_tools" },
             "optimized-tools":  { "type": "boolean", "name": "release_tools" },
             "pch": { "type": "boolean", "name": "precompile_header" },
@@ -485,6 +486,12 @@
             "condition": "!config.msvc && (features.debug || features.debug_and_release) && tests.optimize_debug",
             "output": [ "privateConfig" ]
         },
+        "optimize_size": {
+            "label": "Optimize release build for size",
+            "autoDetect": false,
+            "condition": "!features.debug || features.debug_and_release",
+            "output": [ "privateConfig" ]
+        },
         "architecture": {
             "label": "Architecture",
             "output": [ "architecture" ]
@@ -1090,6 +1097,11 @@ Configure with '-qreal float' to create a build that is binary-compatible with 5
                     "args": "optimize_debug",
                     "condition": "!config.msvc && (features.debug || features.debug_and_release)"
                 },
+                {
+                    "type": "feature",
+                    "args": "optimize_size",
+                    "condition": "!features.debug || features.debug_and_release"
+                },
                 "shared",
                 {
                     "message": "Using C++ standard",

mkspecs/common/gcc-base.conf

@@ -34,6 +34,7 @@
 QMAKE_CFLAGS_OPTIMIZE      = -O2
 QMAKE_CFLAGS_OPTIMIZE_FULL = -O3
 QMAKE_CFLAGS_OPTIMIZE_DEBUG = -Og
+QMAKE_CFLAGS_OPTIMIZE_SIZE = -Os
 
 QMAKE_CFLAGS               += -pipe
 QMAKE_CFLAGS_DEPS          += -M

mkspecs/common/msvc-desktop.conf

@@ -19,6 +19,9 @@ contains(QMAKE_TARGET.arch, x86_64) {
     QMAKE_COMPILER_DEFINES += _WIN64
 }
 
+QMAKE_CFLAGS_OPTIMIZE      = -O2
+QMAKE_CFLAGS_OPTIMIZE_SIZE = -O1
+
 QMAKE_CC                = cl
 QMAKE_LEX               = flex
 QMAKE_LEXFLAGS          =
@@ -27,8 +30,8 @@ QMAKE_YACCFLAGS         = -d
 QMAKE_CFLAGS            = -nologo -Zc:wchar_t
 QMAKE_CFLAGS_WARN_ON    = -W3
 QMAKE_CFLAGS_WARN_OFF   = -W0
-QMAKE_CFLAGS_RELEASE    = -O2 -MD
-QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += -O2 -MD -Zi
+QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE -MD
+QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += $$QMAKE_CFLAGS_OPTIMIZE -MD -Zi
 QMAKE_CFLAGS_DEBUG      = -Zi -MDd
 QMAKE_CFLAGS_YACC       =
 QMAKE_CFLAGS_LTCG       = -GL

mkspecs/features/default_post.prf

@@ -38,7 +38,14 @@ force_debug_info {
     QMAKE_LFLAGS_RELEASE = $$QMAKE_LFLAGS_RELEASE_WITH_DEBUGINFO
 }
 
-optimize_full {
+optimize_size {
+    !isEmpty(QMAKE_CFLAGS_OPTIMIZE):!isEmpty(QMAKE_CFLAGS_OPTIMIZE_SIZE)  {
+        QMAKE_CFLAGS_RELEASE -= $$QMAKE_CFLAGS_OPTIMIZE
+        QMAKE_CXXFLAGS_RELEASE -= $$QMAKE_CFLAGS_OPTIMIZE
+        QMAKE_CFLAGS_RELEASE += $$QMAKE_CFLAGS_OPTIMIZE_SIZE
+        QMAKE_CXXFLAGS_RELEASE += $$QMAKE_CFLAGS_OPTIMIZE_SIZE
+    }
+} else: optimize_full {
     !isEmpty(QMAKE_CFLAGS_OPTIMIZE):!isEmpty(QMAKE_CFLAGS_OPTIMIZE_FULL)  {
         QMAKE_CFLAGS_RELEASE -= $$QMAKE_CFLAGS_OPTIMIZE
         QMAKE_CXXFLAGS_RELEASE -= $$QMAKE_CFLAGS_OPTIMIZE

mkspecs/linux-icc/qmake.conf

@@ -6,6 +6,9 @@ MAKEFILE_GENERATOR      = UNIX
 
 QMAKE_COMPILER          = gcc intel_icc   # icc pretends to be gcc
 
+QMAKE_CFLAGS_OPTIMIZE      = -O2
+QMAKE_CFLAGS_OPTIMIZE_SIZE = -Os
+
 QMAKE_CC                = icc
 QMAKE_LEX               = flex
 QMAKE_LEXFLAGS          =
@@ -16,7 +19,7 @@ QMAKE_CFLAGS_APP        = -fPIC
 QMAKE_CFLAGS_DEPS       = -M
 QMAKE_CFLAGS_WARN_ON    = -w1 -Wall -Wcheck -wd1572,873,2259,2261,3373
 QMAKE_CFLAGS_WARN_OFF   = -w
-QMAKE_CFLAGS_RELEASE    = -O2
+QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE
 QMAKE_CFLAGS_DEBUG      = -O0 -g
 QMAKE_CFLAGS_SHLIB      = -fPIC
 QMAKE_CFLAGS_STATIC_LIB = $$QMAKE_CFLAGS_SHLIB

mkspecs/macx-icc/qmake.conf

@@ -11,12 +11,15 @@ QMAKE_COMPILER_DEFINES += __APPLE__ __GNUC__
 
 QMAKE_COMPILER          = gcc clang intel_icc   # icc pretends to be gcc and clang
 
+QMAKE_CFLAGS_OPTIMIZE      = -O2
+QMAKE_CFLAGS_OPTIMIZE_SIZE = -Os
+
 QMAKE_CC                = icc
 QMAKE_CFLAGS            =
 QMAKE_CFLAGS_DEPS       = -M
 QMAKE_CFLAGS_WARN_ON    = -w1 -Wcheck -wd654,1572,411,873,1125,2259,2261,3280,3373
 QMAKE_CFLAGS_WARN_OFF   = -w
-QMAKE_CFLAGS_RELEASE    = -O2
+QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE
 QMAKE_CFLAGS_DEBUG      = -g -O0
 QMAKE_CFLAGS_SHLIB      = -fPIC
 QMAKE_CFLAGS_STATIC_LIB = $$QMAKE_CFLAGS_SHLIB