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authorGabriel F. T. Gomes <gftg@linux.vnet.ibm.com>2016-01-22 18:05:05 -0200
committerTulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>2016-03-08 15:30:28 -0300
commit183a34dc4a07cad723cd78e494d16a5ef0b6a63e (patch)
treeddbc585df379835c6347b72cf6c3ebf9d781fb16 /sysdeps/powerpc/bits
parent911569d02dec023d949d96aa7b0e828c91c06f55 (diff)
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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.
Diffstat (limited to 'sysdeps/powerpc/bits')
-rw-r--r--sysdeps/powerpc/bits/fenvinline.h16
1 files changed, 10 insertions, 6 deletions
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__ */