[PATCH] Add PowerPC configuration option --with-long-double-format={ibm,ieee}

[Michael Meissner]

On Wed, Jan 10, 2018 at 11:48:30PM +0000, Joseph Myers wrote:
> On Wed, 10 Jan 2018, Michael Meissner wrote:
> 
> > This patch is next in my series of patches to enable us to configure the long
> > double type on PowerPC systems.  This patch is only about the configuration
> > option.  A future patch will contain the multilib support.
> 
> In general we expect configure options to be documented in install.texi.  
> Is this one being deliberately omitted because it is only actually usable 
> for toolchain development at present, with various ways in which the 
> support for IEEE long double is not yet completely functional and library 
> support is missing - with documentation intended to be added later once 
> fully functional?

Here is the first pass at documentation.  Segher is this ok?

2018-01-11  Michael Meissner  <meissner@linux.vnet.ibm.com>

	* doc/install.texi (--with-long-double-format=): Document the
	switch, and note it isn't for general use at the moment.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.vnet.ibm.com, phone: +1 (978) 899-4797
-------------- next part --------------
Index: gcc/doc/install.texi
===================================================================
--- gcc/doc/install.texi	(revision 256556)
+++ gcc/doc/install.texi	(working copy)
@@ -1877,6 +1877,18 @@ When neither of these configure options
 128-bit @code{long double} when built against GNU C Library 2.4 and later,
 64-bit @code{long double} otherwise.
 
+@item --with-long-double-format=ibm
+@itemx --with-long-double-format=ieee
+Specify what format 128-bit @code{long double} should use on PowerPC
+VSX systems, If you use @code{--with-long-double-format=ibm},
+@code{long double} will be IBM extended double, which consists of a
+pair of @code{double} values to give a larger mantissa range.  If you
+use @code{--with-long-double-format=ieee}, @code{long double} will use
+the IEEE 128-bit floating point format.  At the present time, this
+option is only useful for people adding support to the compiler and
+libraries to ultimately switch to the IEEE 128-bit floating point
+format in the future.
+
 @item --enable-fdpic
 On SH Linux systems, generate ELF FDPIC code.