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commit 0b3c9e57a41d9f7c26fb6aa45b99f671bef9c7e0
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Author: Paul A. Clarke <pc@us.ibm.com>
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Date: Tue Aug 20 15:57:35 2019 -0500
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[powerpc] fegetenv_status: simplify instruction generation
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fegetenv_status() wants to use the lighter weight instruction 'mffsl'
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for reading the Floating-Point Status and Control Register (FPSCR).
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It currently will use it directly if compiled '-mcpu=power9', and will
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perform a runtime check (cpu_supports("arch_3_00")) otherwise.
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Nicely, it turns out that the 'mffsl' instruction will decode to
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'mffs' on architectures older than "arch_3_00" because the additional
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bits set for 'mffsl' are "don't care" for 'mffs'. 'mffs' is a superset
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of 'mffsl'.
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So, just generate 'mffsl'.
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diff --git a/sysdeps/powerpc/fpu/fenv_libc.h b/sysdeps/powerpc/fpu/fenv_libc.h
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index b244770d115ea7bb..e8d40ea256b6c5bc 100644
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--- a/sysdeps/powerpc/fpu/fenv_libc.h
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+++ b/sysdeps/powerpc/fpu/fenv_libc.h
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@@ -36,9 +36,12 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
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({ fenv_t env; asm volatile ("mffs %0" : "=f" (env)); env; })
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/* Equivalent to fegetenv_register, but only returns bits for
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- status, exception enables, and mode. */
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-
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-#define fegetenv_status_ISA300() \
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+ status, exception enables, and mode.
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+ Nicely, it turns out that the 'mffsl' instruction will decode to
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+ 'mffs' on architectures older than "power9" because the additional
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+ bits set for 'mffsl' are "don't care" for 'mffs'. 'mffs' is a superset
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+ of 'mffsl'. */
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+#define fegetenv_status() \
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({register double __fr; \
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__asm__ __volatile__ ( \
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".machine push; .machine \"power9\"; mffsl %0; .machine pop" \
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@@ -46,18 +49,6 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
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__fr; \
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})
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-#ifdef _ARCH_PWR9
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-# define fegetenv_status() fegetenv_status_ISA300()
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-#elif defined __BUILTIN_CPU_SUPPORTS__
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-# define fegetenv_status() \
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- (__glibc_likely (__builtin_cpu_supports ("arch_3_00")) \
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- ? fegetenv_status_ISA300() \
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- : fegetenv_register() \
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- )
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-#else
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-# define fegetenv_status() fegetenv_register ()
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-#endif
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-
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/* Equivalent to fesetenv, but takes a fenv_t instead of a pointer. */
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#define fesetenv_register(env) \
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do { \
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