From: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Subject: asm-generic: force inlining of get_order() to work around gcc10 poor decision
When building mpc885_ads_defconfig with gcc 10.1,
the function get_order() appears 50 times in vmlinux:
[linux]# ppc-linux-objdump -x vmlinux | grep get_order | wc -l
50
[linux]# size vmlinux
text data bss dec hex filename
3842620 675624 135160 4653404 47015c vmlinux
In the old days, marking a function 'static inline' was forcing
GCC to inline, but since commit ac7c3e4ff401 ("compiler: enable
CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline
a function.
It looks like GCC 10 is taking poor decisions on this.
get_order() compiles into the following tiny function,
occupying 20 bytes of text.
0000007c <get_order>:
7c: 38 63 ff ff addi r3,r3,-1
80: 54 63 a3 3e rlwinm r3,r3,20,12,31
84: 7c 63 00 34 cntlzw r3,r3
88: 20 63 00 20 subfic r3,r3,32
8c: 4e 80 00 20 blr
By forcing get_order() to be __always_inline, the size of text is
reduced by 1940 bytes, that is almost twice the space occupied by
50 times get_order()
[linux-powerpc]# size vmlinux
text data bss dec hex filename
3840680 675588 135176 4651444 46f9b4 vmlinux
Link: https://lkml.kernel.org/r/96c6172d619c51acc5c1c4884b80785c59af4102.1602949927.git.christophe.leroy@xxxxxxxxxx
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Reviewed-by: Joel Stanley <joel@xxxxxxxxx>
Cc: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/asm-generic/getorder.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/include/asm-generic/getorder.h~asm-generic-force-inlining-of-get_order-to-work-around-gcc10-poor-decision
+++ a/include/asm-generic/getorder.h
@@ -26,7 +26,7 @@
*
* The result is undefined if the size is 0.
*/
-static inline __attribute_const__ int get_order(unsigned long size)
+static __always_inline __attribute_const__ int get_order(unsigned long size)
{
if (__builtin_constant_p(size)) {
if (!size)
_
