arm: Use builtins for ffs/fls
Since ARMv5, the clz instruction allows for efficient implementation of
ffs/fls with builtins. Until ARMv7 (with Thumb-2), this instruction is
only available in ARM mode. LTO makes it difficult to force specific
functions to be in ARM mode, as it is effectively a form of very
aggressive inlining. To work around this, fls/ffs are implemented in
assembly for ARMv5 and ARMv6 when compiling U-Boot in Thumb mode.
Overall, this saves around 75 bytes per call.
This code is synced with v5.15 of the Linux kernel.
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 62cf80f..b1bcd37 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -113,6 +113,11 @@
AFLAGS_REMOVE_memcpy.o := -mthumb -mthumb-interwork
AFLAGS_memset.o := -DMEMSET_NO_THUMB_BUILD
AFLAGS_memcpy.o := -DMEMCPY_NO_THUMB_BUILD
+
+# This is only necessary to force ARM mode on THUMB1 targets.
+ifneq ($(CONFIG_SYS_ARM_ARCH),4)
+obj-y += bitops.o
+endif
endif
endif