On Fri, Sep 30, 2022 at 10:07:59AM -0500, Segher Boessenkool wrote:
> Hi!
>
> On Thu, Sep 29, 2022 at 12:01:43PM +0200, Jakub Jelinek via Gcc-patches wrote:
> > --- gcc/config/i386/i386.cc.jj 2022-09-29 09:13:25.713718513 +0200
> > +++ gcc/config/i386/i386.cc 2022-09-29 11:29:20.828358152 +0200
> > @@ -22725,6 +22725,9 @@ ix86_mangle_type (const_tree type)
> > && TREE_CODE (type) != INTEGER_TYPE && TREE_CODE (type) != REAL_TYPE)
> > return NULL;
> >
> > + if (type == float128_type_node || type == float64x_type_node)
> > + return NULL;
>
> Is float128_type_node always IEEE QP, never double-double? I couldn't
> find this documented anywhere. If this is not true, this part of the
> patch is incorrect.
It is always IEEE quad, if there is no IEEE quad support, it is NULL.
The C++ wording is:
"If the implementation supports an extended floating-point type whose
properties are specified by the ISO/IEC/IEEE 60559 floating-point
interchange format binary128, then the typedef-name std::float128_t is
defined in the header <stdfloat> and names such a type, the macro
__STDCPP_FLOAT128_T__ is defined, and the floating-point literal suffixes
f128 and F128 are supported."
and C:
Types designated:
_FloatN
where N is 16, 32, 64, or ≥128 and a multiple of 32; and, types designated
_DecimalN
where N ≥ 32 and a multiple of 32, are collectively called the interchange
floating types. Each
interchange floating type has the IEC 60559 interchange format corresponding to
its width (N) and
radix (2 for _FloatN, 10 for _DecimalN). Each interchange floating type is not
compatible with any
other type."
So, _Float128 and std::float128_t which we use float128_type_node for
must be IEEE binary128, nothing else.
Internally, it is implemented by using targetm.floatn_mode hook to query
which mode if any is the IEEE one with corresponding width.
Jakub
