Commit f782ddf2 authored Apr 21, 2017 by Christophe Leroy Committed by Michael Ellerman Jun 02, 2017

powerpc: Remove __ilog2()s and use generic ones



With the __ilog2() function as defined in
arch/powerpc/include/asm/bitops.h, GCC will not optimise the code
in case of constant parameter.

The generic ilog2() function in include/linux/log2.h is written
to handle the case of the constant parameter.

This patch discards the three __ilog2() functions and
defines __ilog2() as ilog2()

For non constant calls, the generated code is doing the same:
int test__ilog2(unsigned long x)
{
	return __ilog2(x);
}

int test__ilog2_u32(u32 n)
{
	return __ilog2_u32(n);
}

int test__ilog2_u64(u64 n)
{
	return __ilog2_u64(n);
}

On PPC32 before the patch:
00000000 <test__ilog2>:
   0:	7c 63 00 34 	cntlzw  r3,r3
   4:	20 63 00 1f 	subfic  r3,r3,31
   8:	4e 80 00 20 	blr

0000000c <test__ilog2_u32>:
   c:	7c 63 00 34 	cntlzw  r3,r3
  10:	20 63 00 1f 	subfic  r3,r3,31
  14:	4e 80 00 20 	blr

On PPC32 after the patch:
00000000 <test__ilog2>:
   0:	7c 63 00 34 	cntlzw  r3,r3
   4:	20 63 00 1f 	subfic  r3,r3,31
   8:	4e 80 00 20 	blr

0000000c <test__ilog2_u32>:
   c:	7c 63 00 34 	cntlzw  r3,r3
  10:	20 63 00 1f 	subfic  r3,r3,31
  14:	4e 80 00 20 	blr

On PPC64 before the patch:
0000000000000000 <.test__ilog2>:
   0:	7c 63 00 74 	cntlzd  r3,r3
   4:	20 63 00 3f 	subfic  r3,r3,63
   8:	7c 63 07 b4 	extsw   r3,r3
   c:	4e 80 00 20 	blr

0000000000000010 <.test__ilog2_u32>:
  10:	7c 63 00 34 	cntlzw  r3,r3
  14:	20 63 00 1f 	subfic  r3,r3,31
  18:	7c 63 07 b4 	extsw   r3,r3
  1c:	4e 80 00 20 	blr

0000000000000020 <.test__ilog2_u64>:
  20:	7c 63 00 74 	cntlzd  r3,r3
  24:	20 63 00 3f 	subfic  r3,r3,63
  28:	7c 63 07 b4 	extsw   r3,r3
  2c:	4e 80 00 20 	blr

On PPC64 after the patch:
0000000000000000 <.test__ilog2>:
   0:	7c 63 00 74 	cntlzd  r3,r3
   4:	20 63 00 3f 	subfic  r3,r3,63
   8:	7c 63 07 b4 	extsw   r3,r3
   c:	4e 80 00 20 	blr

0000000000000010 <.test__ilog2_u32>:
  10:	7c 63 00 34 	cntlzw  r3,r3
  14:	20 63 00 1f 	subfic  r3,r3,31
  18:	7c 63 07 b4 	extsw   r3,r3
  1c:	4e 80 00 20 	blr

0000000000000020 <.test__ilog2_u64>:
  20:	7c 63 00 74 	cntlzd  r3,r3
  24:	20 63 00 3f 	subfic  r3,r3,63
  28:	7c 63 07 b4 	extsw   r3,r3
  2c:	4e 80 00 20 	blr

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent 22ef33b3

arch/powerpc/Kconfig

+0 −8

Original line number	Diff line number	Diff line
		@@ -109,14 +109,6 @@ config GENERIC_LOCKBREAK
		default y
		depends on SMP && PREEMPT

		config ARCH_HAS_ILOG2_U32
		bool
		default y

		config ARCH_HAS_ILOG2_U64
		bool
		default y if 64BIT

		config GENERIC_HWEIGHT
		bool
		default y

arch/powerpc/include/asm/bitops.h

+1 −26

Original line number	Diff line number	Diff line
		@@ -206,32 +206,7 @@ static __inline__ void __clear_bit_unlock(int nr, volatile unsigned long *addr)
		* Return the zero-based bit position (LE, not IBM bit numbering) of
		* the most significant 1-bit in a double word.
		*/
		static __inline__ __attribute__((const))
		int __ilog2(unsigned long x)
		{
		int lz;

		asm (PPC_CNTLZL "%0,%1" : "=r" (lz) : "r" (x));
		return BITS_PER_LONG - 1 - lz;
		}

		static inline __attribute__((const))
		int __ilog2_u32(u32 n)
		{
		int bit;
		asm ("cntlzw %0,%1" : "=r" (bit) : "r" (n));
		return 31 - bit;
		}

		#ifdef __powerpc64__
		static inline __attribute__((const))
		int __ilog2_u64(u64 n)
		{
		int bit;
		asm ("cntlzd %0,%1" : "=r" (bit) : "r" (n));
		return 63 - bit;
		}
		#endif
		#define __ilog2(x) ilog2(x)

		#include <asm-generic/bitops/ffz.h>

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