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| author | Gabriel F. T. Gomes <gftg@linux.vnet.ibm.com> | 2016-01-22 18:05:05 -0200 |
|---|---|---|
| committer | Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com> | 2016-03-08 15:30:28 -0300 |
| commit | 183a34dc4a07cad723cd78e494d16a5ef0b6a63e (patch) | |
| tree | ddbc585df379835c6347b72cf6c3ebf9d781fb16 | |
| parent | 911569d02dec023d949d96aa7b0e828c91c06f55 (diff) | |
| download | glibc-183a34dc4a07cad723cd78e494d16a5ef0b6a63e.tar.gz glibc-183a34dc4a07cad723cd78e494d16a5ef0b6a63e.tar.xz glibc-183a34dc4a07cad723cd78e494d16a5ef0b6a63e.zip | |
powerpc: Remove uses of operand modifier (%s) in inline asm
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.
| -rw-r--r-- | ChangeLog | 6 | ||||
| -rw-r--r-- | sysdeps/powerpc/bits/fenvinline.h | 16 |
2 files changed, 16 insertions, 6 deletions
diff --git a/ChangeLog b/ChangeLog index 79a09044b7..585c9c2d2e 100644 --- a/ChangeLog +++ b/ChangeLog @@ -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 diff --git a/sysdeps/powerpc/bits/fenvinline.h b/sysdeps/powerpc/bits/fenvinline.h index 4a7b2af6aa..c283ede060 100644 --- a/sysdeps/powerpc/bits/fenvinline.h +++ b/sysdeps/powerpc/bits/fenvinline.h @@ -32,8 +32,10 @@ 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) \ +# define feraiseexcept(__excepts) \ (__extension__ ({ \ int __e = __excepts; \ int __ret; \ @@ -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 \ @@ -52,7 +54,7 @@ })) /* Inline definition for feclearexcept. */ -# define feclearexcept(__excepts) \ +# define feclearexcept(__excepts) \ (__extension__ ({ \ int __e = __excepts; \ int __ret; \ @@ -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__ */ |