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powerpc: Remove uses of operand modifier (%s) in inline asm

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The operand modifier %s on powerpc is an undocumented internal implementation
detail of GCC.  Besides that, the GCC community wants to remove it.  This patch
rewrites the expressions that use this modifier with logically equivalent
expressions that don't require it.

Explanation for the substitution:

The %s modifier takes an immediate operand and prints 32 less such immediate.
Thus, in the previous code, the expression resulted in:

  32 - __builtin_ffs(e)

where e was guaranteed to have exactly a single bit set, by the following
expressions:

  (e & (e-1) == 0) : e has at most one bit set.
  (e != 0)         : e is not zero, thus it has at least one bit set.

Since we guarantee that there is exactly only one bit set, the following
statement is true:

  32 - __builtin_ffs(e) == __builtin_clz(e)

Thus, we can replace __builtin_ffs with __builtin_clz and remove the %s operand
modifier.
This commit is contained in:
Gabriel F. T. Gomes 2016-01-22 18:05:05 -02:00 committed by Tulio Magno Quites Machado Filho
parent 911569d02d
commit 183a34dc4a
2 changed files with 16 additions and 6 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2016-03-08 Gabriel F. T. Gomes <gftg@linux.vnet.ibm.com>
* sysdeps/powerpc/bits/fenvinline.h (feraiseexcept): Remove use of %s
operand modifier.
(feclearexcept): Likewise.
2016-03-08 Carlos Eduardo Seo <cseo@linux.vnet.ibm.com>
* sysdeps/powerpc/dl-procinfo.c (_dl_powerpc_cap_flags): Updated

12
sysdeps/powerpc/bits/fenvinline.h
View File

@ -32,6 +32,8 @@
warning when __excepts is not a constant. Otherwise, they mean the
same as just plain 'i'. */
# if __GNUC_PREREQ(3, 4)
/* Inline definition for feraiseexcept. */
# define feraiseexcept(__excepts) \
(__extension__ ({ \
@ -42,8 +44,8 @@
&& __e != FE_INVALID) \
{ \
if (__e != 0) \
__asm__ __volatile__ ("mtfsb1 %s0" \
: : "i#*X" (__builtin_ffs (__e))); \
__asm__ __volatile__ ("mtfsb1 %0" \
: : "i#*X" (__builtin_clz (__e))); \
__ret = 0; \
} \
else \
@ -61,8 +63,8 @@
&& __e != FE_INVALID) \
{ \
if (__e != 0) \
__asm__ __volatile__ ("mtfsb0 %s0" \
: : "i#*X" (__builtin_ffs (__e))); \
__asm__ __volatile__ ("mtfsb0 %0" \
: : "i#*X" (__builtin_clz (__e))); \
__ret = 0; \
} \
else \
@ -70,6 +72,8 @@
__ret; \
}))
# endif /* __GNUC_PREREQ(3, 4). */
# endif /* !__NO_MATH_INLINES. */
#endif /* __GNUC__ && !_SOFT_FLOAT && !__NO_FPRS__ */