[PATCH v2] build system: allow users to select the optimization mode

[Bartosz Golaszewski]

In some scenarios busybox performance may be prefered over its
small size.

Allow users to select the compiler optimization level by adding
appropriate config options.

Signed-off-by: Bartosz Golaszewski <bartekgola at gmail.com>
---
version 2:
- make the choice simplier for less advanced users by leaving only
  the choice between optimization for speed and optimization for
  size (default)

version 1:
http://lists.busybox.net/pipermail/busybox/2015-April/082765.html

 Config.in      | 25 +++++++++++++++++++++++++
 Makefile.flags | 10 +++++-----
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/Config.in b/Config.in
index 07b4bf3..227fc78 100644
--- a/Config.in
+++ b/Config.in
@@ -514,6 +514,31 @@ config PIE
 
 	  Most people will leave this set to 'N'.
 
+choice
+	prompt "Compiler optimization"
+	default OPTIMIZE_SIZE
+	help
+	  Set the compiler optimization mode.
+
+config OPTIMIZE_SIZE
+	bool "Optimize for size"
+	help
+	  Optimize for size. This enables all standard speed
+	  optimizations that do not typically increase code size.
+	  It also performs further optimizations designed to reduce
+	  code size.
+
+	  This is the default for busybox.
+
+config OPTIMIZE_SPEED
+	bool "Optimize for speed"
+	help
+	  Perform nearly all supported optimizations that do not involve
+	  a space-speed tradeoff. This option increases both compilation
+	  time and the performance of the generated code.
+
+endchoice
+
 config NOMMU
 	bool "Force NOMMU build"
 	default n
diff --git a/Makefile.flags b/Makefile.flags
index a1ed148..a7eaee1 100644
--- a/Makefile.flags
+++ b/Makefile.flags
@@ -61,17 +61,17 @@ CFLAGS += $(call cc-option,-fno-asynchronous-unwind-tables,)
 # be fixed..
 #CFLAGS += $(call cc-option,-Wconversion,)
 
-ifneq ($(CONFIG_DEBUG),y)
-CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
-else
+ifeq ($(CONFIG_DEBUG),y)
 CFLAGS += $(call cc-option,-g,)
-#CFLAGS += "-D_FORTIFY_SOURCE=2"
+endif
+
 ifeq ($(CONFIG_DEBUG_PESSIMIZE),y)
 CFLAGS += $(call cc-option,-O0,)
+else ifeq ($(CONFIG_OPTIMIZE_SPEED),y)
+CFLAGS += $(call cc-option,-O2,)
 else
 CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
 endif
-endif
 
 # If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
 ARCH_FPIC ?= -fpic
-- 
2.1.4