[powerpc] fegetenv_and_set_rn now uses the builtins provided by GCC.
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Commit Message
On powerpc, SET_RESTORE_ROUND uses inline assembly to optimize the
prologue get/save/set rounding mode operations for POWER9 and
later by using 'mffscrn' where possible, this was introduced by
commit f1c56cdff09f650ad721fae026eb6a3651631f3d.
GCC version 14 onwards supports builtins as __builtin_set_fpscr_rn
which now returns the FPSCR fields in a double. This feature is
available on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro
is defined.
GCC commit ef3bbc69d15707e4db6e2f198c621effb636cc26 adds
this feature.
Changes are done to use __builtin_set_fpscr_rn instead of mffscrn
or mffscrni in __fe_mffscrn(rn).
Suggested-by: Carl Love <cel@us.ibm.com>
---
sysdeps/powerpc/fpu/fenv_libc.h | 9 +++++++++
1 file changed, 9 insertions(+)
Comments
On 23/09/23 12:49, Manjunath Matti wrote:
> On powerpc, SET_RESTORE_ROUND uses inline assembly to optimize the
> prologue get/save/set rounding mode operations for POWER9 and
> later by using 'mffscrn' where possible, this was introduced by
> commit f1c56cdff09f650ad721fae026eb6a3651631f3d.
>
> GCC version 14 onwards supports builtins as __builtin_set_fpscr_rn
> which now returns the FPSCR fields in a double. This feature is
> available on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro
> is defined.
> GCC commit ef3bbc69d15707e4db6e2f198c621effb636cc26 adds
> this feature.
>
> Changes are done to use __builtin_set_fpscr_rn instead of mffscrn
> or mffscrni in __fe_mffscrn(rn).
>
> Suggested-by: Carl Love <cel@us.ibm.com>
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> sysdeps/powerpc/fpu/fenv_libc.h | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/sysdeps/powerpc/fpu/fenv_libc.h b/sysdeps/powerpc/fpu/fenv_libc.h
> index fa5e1c697e..a2a12d914b 100644
> --- a/sysdeps/powerpc/fpu/fenv_libc.h
> +++ b/sysdeps/powerpc/fpu/fenv_libc.h
> @@ -68,6 +68,14 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
> __fr; \
> })
>
> +/* Starting with GCC 14 __builtin_set_fpscr_rn can be used to return the
> + FPSCR fields as a double. This support is available
> + on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro is defined.
> + To retain backward compatibility with older GCC, we still retain the
> + old inline assembly implementation.*/
> +#ifdef __SET_FPSCR_RN_RETURNS_FPSCR__
> +#define __fe_mffscrn(rn) __builtin_set_fpscr_rn (rn)
> +#else
> #define __fe_mffscrn(rn) \
> ({register fenv_union_t __fr; \
> if (__builtin_constant_p (rn)) \
> @@ -83,6 +91,7 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
> } \
> __fr.fenv; \
> })
> +#endif
>
> /* Like fegetenv_control, but also sets the rounding mode. */
> #ifdef _ARCH_PWR9
On 9/23/23 10:49 AM, Manjunath Matti wrote:
> GCC version 14 onwards supports builtins as __builtin_set_fpscr_rn
> which now returns the FPSCR fields in a double. This feature is
> available on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro
> is defined.
The last sentence is not completely correct, since the feature is available
on pre-Power9 cpus too. The first sentence could be worded a little better
too. How about:
GCC version 14 onwards supports the __builtin_set_fpscr_rn built-in,
which now returns the FPSCR fields in a double. This feature is
available when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro is defined.
Peter
@@ -68,6 +68,14 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
__fr; \
})
+/* Starting with GCC 14 __builtin_set_fpscr_rn can be used to return the
+ FPSCR fields as a double. This support is available
+ on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro is defined.
+ To retain backward compatibility with older GCC, we still retain the
+ old inline assembly implementation.*/
+#ifdef __SET_FPSCR_RN_RETURNS_FPSCR__
+#define __fe_mffscrn(rn) __builtin_set_fpscr_rn (rn)
+#else
#define __fe_mffscrn(rn) \
({register fenv_union_t __fr; \
if (__builtin_constant_p (rn)) \
@@ -83,6 +91,7 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
} \
__fr.fenv; \
})
+#endif
/* Like fegetenv_control, but also sets the rounding mode. */
#ifdef _ARCH_PWR9