https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91690
kargl at gcc dot gnu.org changed:
What |Removed |Added
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CC| |kargl at gcc dot gnu.org
--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to Rich Townsend from comment #0)
> Created attachment 46844 [details]
> Demo program
>
> The intrinsics provided by the IEEE_ARITHMETIC module appear to be
> significantly slower than an equivalent implementation based on inspecting
> bits.
>
The implementations are not equivalent. -fdump-tree-original may
shield some light.
is_nan_bits() isn't worried about FPU state (ie., keeping track of
exceptions). is_nan_bits is reduced to something simply using simple
bit twiddling. The following is somewhat edited to reduce length
is_nan_bits (real(kind=4) & x)
{
integer(kind=4) expn, frac, is_nan, ix, sign;
{
integer(kind=8) D.3904, D.3905, D.3906, transfer.0;
D.3904 = 4;
D.3905 = 4;
__builtin_memcpy ((void *) &transfer.0, (void *) x,
(unsigned long) MAX_EXPR <MIN_EXPR <D.3905, D.3904>, 0>);
ix = transfer.0;
}
frac = NON_LVALUE_EXPR <ix> & 8388607;
expn = ix >> 23 & 255;
sign = (integer(kind=4)) ((unsigned int) ix >> 31);
is_nan = expn == 255 && frac != 0;
return is_nan;
}
is_nan_ieee is reduced to something with 2 function calls
to maintain fpu state.
is_nan_ieee (real(kind=4) & restrict x)
{
c_char fpstate.1[33];
logical(kind=4) is_nan;
try
{
_gfortran_ieee_procedure_entry ((void *) &fpstate.1);
is_nan = SAVE_EXPR <*x> unord SAVE_EXPR <*x>;
return is_nan;
}
finally
{
_gfortran_ieee_procedure_exit ((void *) &fpstate.1);
}
}
Both _entry and _exit are manipulating the FPU.
