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Date: Wed, 21 Dec 2022 21:40:24 +0000
From: Joseph Myers <joseph@codesourcery.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
CC: Kewen.Lin <linkw@linux.ibm.com>, GCC Patches <gcc-patches@gcc.gnu.org>,
	Michael Meissner <meissner@linux.ibm.com>, David Edelsohn
	<dje.gcc@gmail.com>, Jakub Jelinek <jakub@redhat.com>, Peter Bergner
	<bergner@linux.ibm.com>, Richard Biener <richard.guenther@gmail.com>, Richard
 Sandiford <richard.sandiford@arm.com>
Subject: Re: [RFC/PATCH] Remove the workaround for _Float128 precision
 [PR107299]
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References: <718677e7-614d-7977-312d-05a75e1fd5b4@linux.ibm.com> <20221221212407.GU25951@gate.crashing.org>
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On Wed, 21 Dec 2022, Segher Boessenkool wrote:

> > --- a/gcc/tree.cc
> > +++ b/gcc/tree.cc
> > @@ -9442,15 +9442,6 @@ build_common_tree_nodes (bool signed_char)
> >        if (!targetm.floatn_mode (n, extended).exists (&mode))
> >  	continue;
> >        int precision = GET_MODE_PRECISION (mode);
> > -      /* Work around the rs6000 KFmode having precision 113 not
> > -	 128.  */
> 
> It has precision 126 now fwiw.
> 
> Joseph: what do you think about this patch?  Is the workaround it
> removes still useful in any way, do we need to do that some other way if
> we remove this?

I think it's best for the TYPE_PRECISION, for any type with the binary128 
format, to be 128 (not 126).

It's necessary that _Float128, _Float64x and long double all have the same 
TYPE_PRECISION when they have the same (binary128) format, or at least 
that TYPE_PRECISION for _Float128 >= that for long double >= that for 
_Float64x, so that the rules in c_common_type apply properly.

How the TYPE_PRECISION compares to that of __ibm128, or of long double 
when that's double-double, is less important.

-- 
Joseph S. Myers
joseph@codesourcery.com