kbuild,arc: add CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 for ARC

arch/arc/Makefile overrides -O2 with -O3. This is the only user of
ARCH_CFLAGS. There is no user of ARCH_CPPFLAGS or ARCH_AFLAGS.
My plan is to remove ARCH_{CPP,A,C}FLAGS after refactoring the ARC
Makefile.

Currently, ARC has no way to enable -Wmaybe-uninitialized because both
-O3 and -Os disable it. Enabling it will be useful for compile-testing.
This commit allows allmodconfig (, which defaults to -O2) to enable it.

Add CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y to all the defconfig files
in arch/arc/configs/ in order to keep the current config settings.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>

Makefile

@@ -723,10 +723,12 @@ KBUILD_CFLAGS	+= $(call cc-disable-warning, format-truncation)
 KBUILD_CFLAGS	+= $(call cc-disable-warning, format-overflow)
 KBUILD_CFLAGS	+= $(call cc-disable-warning, address-of-packed-member)
 
-ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
-KBUILD_CFLAGS	+= -Os
-else
-KBUILD_CFLAGS   += -O2
+ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
+KBUILD_CFLAGS += -O2
+else ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3
+KBUILD_CFLAGS += -O3
+else ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
+KBUILD_CFLAGS += -Os
 endif
 
 ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED

arch/arc/Makefile

@@ -48,14 +48,6 @@ endif
 cfi := $(call as-instr,.cfi_startproc\n.cfi_endproc,-DARC_DW2_UNWIND_AS_CFI)
 cflags-$(CONFIG_ARC_DW2_UNWIND)		+= -fasynchronous-unwind-tables $(cfi)
 
-ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
-# Generic build system uses -O2, we want -O3
-# Note: No need to add to cflags-y as that happens anyways
-#
-# Disable the false maybe-uninitialized warings gcc spits out at -O3
-ARCH_CFLAGS += -O3 $(call cc-disable-warning,maybe-uninitialized,)
-endif
-
 # small data is default for elf32 tool-chain. If not usable, disable it
 # This also allows repurposing GP as scratch reg to gcc reg allocator
 disable_small_data := y

arch/arc/configs/axs101_defconfig

@@ -9,6 +9,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/axs103_defconfig

@@ -9,6 +9,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/axs103_smp_defconfig

@@ -9,6 +9,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/haps_hs_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EXPERT=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_COMPAT_BRK is not set

arch/arc/configs/haps_hs_smp_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/hsdk_defconfig

@@ -9,6 +9,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
 CONFIG_BLK_DEV_RAM=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/nps_defconfig

@@ -6,6 +6,7 @@ CONFIG_HIGH_RES_TIMERS=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_SYSCTL_SYSCALL=y
 # CONFIG_EPOLL is not set
 # CONFIG_SIGNALFD is not set

arch/arc/configs/nsim_700_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_KALLSYMS_ALL=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y

arch/arc/configs/nsim_hs_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_KALLSYMS_ALL=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y

arch/arc/configs/nsim_hs_smp_defconfig

@@ -8,6 +8,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_KALLSYMS_ALL=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y

arch/arc/configs/nsimosci_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_KALLSYMS_ALL=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y

arch/arc/configs/nsimosci_hs_defconfig

@@ -10,6 +10,7 @@ CONFIG_NAMESPACES=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_KALLSYMS_ALL=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y

arch/arc/configs/nsimosci_hs_smp_defconfig

@@ -8,6 +8,7 @@ CONFIG_IKCONFIG_PROC=y
 # CONFIG_UTS_NS is not set
 # CONFIG_PID_NS is not set
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_COMPAT_BRK is not set
 CONFIG_KPROBES=y

arch/arc/configs/tb10x_defconfig

@@ -14,6 +14,7 @@ CONFIG_INITRAMFS_SOURCE="../tb10x-rootfs.cpio"
 CONFIG_INITRAMFS_ROOT_UID=2100
 CONFIG_INITRAMFS_ROOT_GID=501
 # CONFIG_RD_GZIP is not set
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_SYSCTL_SYSCALL=y
 CONFIG_KALLSYMS_ALL=y
 # CONFIG_AIO is not set

arch/arc/configs/vdk_hs38_defconfig

@@ -4,6 +4,7 @@ CONFIG_HIGH_RES_TIMERS=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

arch/arc/configs/vdk_hs38_smp_defconfig

@@ -4,6 +4,7 @@ CONFIG_HIGH_RES_TIMERS=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_BLK_DEV_INITRD=y
+CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3=y
 CONFIG_EMBEDDED=y
 CONFIG_PERF_EVENTS=y
 # CONFIG_VM_EVENT_COUNTERS is not set

init/Kconfig

@@ -1209,14 +1209,22 @@ choice
 	default CC_OPTIMIZE_FOR_PERFORMANCE
 
 config CC_OPTIMIZE_FOR_PERFORMANCE
-	bool "Optimize for performance"
+	bool "Optimize for performance (-O2)"
 	help
 	  This is the default optimization level for the kernel, building
 	  with the "-O2" compiler flag for best performance and most
 	  helpful compile-time warnings.
 
+config CC_OPTIMIZE_FOR_PERFORMANCE_O3
+	bool "Optimize more for performance (-O3)"
+	depends on ARC
+	imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED  # avoid false positives
+	help
+	  Choosing this option will pass "-O3" to your compiler to optimize
+	  the kernel yet more for performance.
+
 config CC_OPTIMIZE_FOR_SIZE
-	bool "Optimize for size"
+	bool "Optimize for size (-Os)"
 	imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED  # avoid false positives
 	help
 	  Choosing this option will pass "-Os" to your compiler resulting