linux-kernel - [PATCH] powerpc/bitops: Force inlining of fls()

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Message-Id: <adc9c9d6378f6b5008246ca717993d7870188efb.1644569473.git.christophe.leroy@csgroup.eu>
Date:   Fri, 11 Feb 2022 09:51:32 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/bitops: Force inlining of fls()

Building a kernel with CONFIG_CC_OPTIMISE_FOR_SIZE leads to
the following functions being copied several times in vmlinux:

	31 times __ilog2_u32()
	34 times fls()

Disassembly follows:

	c00f476c <fls>:
	c00f476c:	7c 63 00 34 	cntlzw  r3,r3
	c00f4770:	20 63 00 20 	subfic  r3,r3,32
	c00f4774:	4e 80 00 20 	blr

	c00f4778 <__ilog2_u32>:
	c00f4778:	94 21 ff f0 	stwu    r1,-16(r1)
	c00f477c:	7c 08 02 a6 	mflr    r0
	c00f4780:	90 01 00 14 	stw     r0,20(r1)
	c00f4784:	4b ff ff e9 	bl      c00f476c <fls>
	c00f4788:	80 01 00 14 	lwz     r0,20(r1)
	c00f478c:	38 63 ff ff 	addi    r3,r3,-1
	c00f4790:	7c 08 03 a6 	mtlr    r0
	c00f4794:	38 21 00 10 	addi    r1,r1,16
	c00f4798:	4e 80 00 20 	blr

When forcing inlining of fls(), we get

	c0008b80 <__ilog2_u32>:
	c0008b80:	7c 63 00 34 	cntlzw  r3,r3
	c0008b84:	20 63 00 1f 	subfic  r3,r3,31
	c0008b88:	4e 80 00 20 	blr

vmlinux size gets reduced by 1 kbyte with that change.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/include/asm/bitops.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h
index f18b1eac6b54..7df7fee774e5 100644
--- a/arch/powerpc/include/asm/bitops.h
+++ b/arch/powerpc/include/asm/bitops.h
@@ -288,7 +288,7 @@ static __always_inline void arch___clear_bit_unlock(int nr, volatile unsigned lo
  * fls: find last (most-significant) bit set.
  * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
  */
-static inline int fls(unsigned int x)
+static __always_inline int fls(unsigned int x)
 {
 	int lz;
 
@@ -306,7 +306,7 @@ static inline int fls(unsigned int x)
  * 32-bit fls calls.
  */
 #ifdef CONFIG_PPC64
-static inline int fls64(__u64 x)
+static __always_inline int fls64(__u64 x)
 {
 	int lz;
 
-- 
2.34.1