On 02/17/2016 08:37 PM, Alan Modra wrote:
>> +/* A set bit indicates an exception is trapping. */
>> +# define FP_TRAPPING_EXCEPTIONS ((_fpscr.i << 22) & FP_EX_ALL)
>
> why then a shift here, since FP_EX_* are defined as the actual
> register bits? Oh, I see. FP_EX_* are the status bits, and you want
> the enable bits. ie. bit 56 rather than bit 34, bit 57 rather than
> bit 35 and so on (bits numbered from 0 as msb). A comment to that
> effect might reduce head scratching.
Thanks for taking a look Alan, and Joseph. I've expanded the comment
to clarify the otherwise mysterious shift with the updated patch.
libgcc
* config/rs6000/sfp-machine.h:
(_FP_DECL_EX): Declare _fpsr as a union of u64 and double.
(FP_TRAPPING_EXCEPTIONS): Return a bitmask of trapping
exceptions.
(FP_INIT_ROUNDMODE): Read the fpscr instead of writing
a mystery value.
(FP_ROUNDMODE): Update the usage of _fpscr.
diff --git a/libgcc/config/rs6000/sfp-machine.h b/libgcc/config/rs6000/sfp-machine.h
index 75d5e1a..8dd8ea3 100644
--- a/libgcc/config/rs6000/sfp-machine.h
+++ b/libgcc/config/rs6000/sfp-machine.h
@@ -130,9 +130,13 @@ void __sfp_handle_exceptions (int);
if (__builtin_expect (_fex, 0)) \
__sfp_handle_exceptions (_fex); \
} while (0);
-/* A set bit indicates an exception is masked and a clear bit indicates it is
- trapping. */
-# define FP_TRAPPING_EXCEPTIONS (~_fpscr & (FP_EX_ALL >> 22))
+
+/* The FP_EX_* bits track whether the exception has occurred. This macro
+ must set the FP_EX_* bits of those exceptions which are configured to
+ trap. The FPSCR bit which indicates this is 22 ISA bits above the
+ respective FP_EX_* bit. Note, the ISA labels bits from msb to lsb,
+ so 22 ISA bits above is 22 bits below when counted from the lsb. */
+# define FP_TRAPPING_EXCEPTIONS ((_fpscr.i << 22) & FP_EX_ALL)
# define FP_RND_NEAREST 0x0
# define FP_RND_ZERO 0x1
@@ -141,16 +145,16 @@ void __sfp_handle_exceptions (int);
# define FP_RND_MASK 0x3
# define _FP_DECL_EX \
- unsigned long long _fpscr __attribute__ ((unused)) = FP_RND_NEAREST
+ union { unsigned long long i; double d; } _fpscr __attribute__ ((unused)) = \
+ { .i = FP_RND_NEAREST }
#define FP_INIT_ROUNDMODE \
do { \
- __asm__ __volatile__ ("mtfsf 255, %0" \
- : \
- : "f" (_fpscr)); \
+ __asm__ __volatile__ ("mffs %0" \
+ : "=f" (_fpscr.d)); \
} while (0)
-# define FP_ROUNDMODE (_fpscr & FP_RND_MASK)
+# define FP_ROUNDMODE (_fpscr.i & FP_RND_MASK)
#endif /* !__FLOAT128__ */
/* Define ALIASNAME as a strong alias for NAME. */
