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powerpc: Use builtin functions for fls()/__fls()/fls64()

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

This patch replaces __fls() by the builtin function, and modifies
fls() and fls64() to use builtins instead of inline assembly

For non constant calls, the generated code is doing the same:

int testfls(unsigned int x)
{
	return fls(x);
}

unsigned long test__fls(unsigned long x)
{
	return __fls(x);
}

int testfls64(__u64 x)
{
	return fls64(x);
}

On PPC32, before the patch:
00000064 <testfls>:
  64:	7c 63 00 34 	cntlzw  r3,r3
  68:	20 63 00 20 	subfic  r3,r3,32
  6c:	4e 80 00 20 	blr

00000070 <test__fls>:
  70:	7c 63 00 34 	cntlzw  r3,r3
  74:	20 63 00 1f 	subfic  r3,r3,31
  78:	4e 80 00 20 	blr

0000007c <testfls64>:
  7c:	2c 03 00 00 	cmpwi   r3,0
  80:	40 82 00 10 	bne     90 <testfls64+0x14>
  84:	7c 83 00 34 	cntlzw  r3,r4
  88:	20 63 00 20 	subfic  r3,r3,32
  8c:	4e 80 00 20 	blr
  90:	7c 63 00 34 	cntlzw  r3,r3
  94:	20 63 00 40 	subfic  r3,r3,64
  98:	4e 80 00 20 	blr

On PPC32, after the patch:
00000054 <testfls>:
  54:	7c 63 00 34 	cntlzw  r3,r3
  58:	20 63 00 20 	subfic  r3,r3,32
  5c:	4e 80 00 20 	blr

00000060 <test__fls>:
  60:	7c 63 00 34 	cntlzw  r3,r3
  64:	20 63 00 1f 	subfic  r3,r3,31
  68:	4e 80 00 20 	blr

0000006c <testfls64>:
  6c:	2c 03 00 00 	cmpwi   r3,0
  70:	41 82 00 10 	beq     80 <testfls64+0x14>
  74:	7c 63 00 34 	cntlzw  r3,r3
  78:	20 63 00 40 	subfic  r3,r3,64
  7c:	4e 80 00 20 	blr
  80:	7c 83 00 34 	cntlzw  r3,r4
  84:	20 63 00 40 	subfic  r3,r3,32
  88:	4e 80 00 20 	blr

On PPC64, before the patch:
00000000000000a0 <.testfls>:
  a0:	7c 63 00 34 	cntlzw  r3,r3
  a4:	20 63 00 20 	subfic  r3,r3,32
  a8:	7c 63 07 b4 	extsw   r3,r3
  ac:	4e 80 00 20 	blr

00000000000000b0 <.test__fls>:
  b0:	7c 63 00 74 	cntlzd  r3,r3
  b4:	20 63 00 3f 	subfic  r3,r3,63
  b8:	7c 63 07 b4 	extsw   r3,r3
  bc:	4e 80 00 20 	blr

00000000000000c0 <.testfls64>:
  c0:	7c 63 00 74 	cntlzd  r3,r3
  c4:	20 63 00 40 	subfic  r3,r3,64
  c8:	7c 63 07 b4 	extsw   r3,r3
  cc:	4e 80 00 20 	blr

On PPC64, after the patch:
0000000000000090 <.testfls>:
  90:	7c 63 00 34 	cntlzw  r3,r3
  94:	20 63 00 20 	subfic  r3,r3,32
  98:	7c 63 07 b4 	extsw   r3,r3
  9c:	4e 80 00 20 	blr

00000000000000a0 <.test__fls>:
  a0:	7c 63 00 74 	cntlzd  r3,r3
  a4:	20 63 00 3f 	subfic  r3,r3,63
  a8:	4e 80 00 20 	blr
  ac:	60 00 00 00 	nop

00000000000000b0 <.testfls64>:
  b0:	7c 63 00 74 	cntlzd  r3,r3
  b4:	20 63 00 40 	subfic  r3,r3,64
  b8:	7c 63 07 b4 	extsw   r3,r3
  bc:	4e 80 00 20 	blr

Those builtins have been in GCC since at least 3.4.6 (see
https://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Other-Builtins.html )

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christophe Leroy 2017-04-21 13:18:48 +02:00 committed by Michael Ellerman
parent f83647d642
commit 2fcff790dc
1 changed files with 3 additions and 21 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

24
arch/powerpc/include/asm/bitops.h
View file

@ -263,33 +263,15 @@ static __inline__ unsigned long ffz(unsigned long x)
*/
static __inline__ int fls(unsigned int x)
{
int lz;
asm ("cntlzw %0,%1" : "=r" (lz) : "r" (x));
return 32 - lz;
return 32 - __builtin_clz(x);
}
static __inline__ unsigned long __fls(unsigned long x)
{
return __ilog2(x);
}
#include <asm-generic/bitops/builtin-__fls.h>
/*
* 64-bit can do this using one cntlzd (count leading zeroes doubleword)
* instruction; for 32-bit we use the generic version, which does two
* 32-bit fls calls.
*/
#ifdef __powerpc64__
static __inline__ int fls64(__u64 x)
{
int lz;
asm ("cntlzd %0,%1" : "=r" (lz) : "r" (x));
return 64 - lz;
return 64 - __builtin_clzll(x);
}
#else
#include <asm-generic/bitops/fls64.h>
#endif /* __powerpc64__ */
#ifdef CONFIG_PPC64
unsigned int __arch_hweight8(unsigned int w);