Document the xorsign optab.

2018-11-27  Tamar Christina  <tamar.christina@arm.com>

	* doc/md.texi (xorsign): Document it.

From-SVN: r266510

gcc/ChangeLog

+2018-11-27  Tamar Christina  <tamar.christina@arm.com>
+
+	* doc/md.texi (xorsign): Document it.
+
 2018-11-27  Martin Liska  <mliska@suse.cz>
 
 	* config/gnu-user.h (TARGET_F951_OPTIONS): New.

gcc/doc/md.texi

@@ -6022,6 +6022,15 @@ vector floating-point mode.
 
 This pattern is not allowed to @code{FAIL}.
 
+@cindex @code{xorsign@var{m}3} instruction pattern
+@item @samp{xorsign@var{m}3}
+Equivalent to @samp{op0 = op1 * copysign (1.0, op2)}: store a value with
+the magnitude of operand 1 and the sign of operand 2 into operand 0.
+All operands have mode @var{m}, which is a scalar or vector
+floating-point mode.
+
+This pattern is not allowed to @code{FAIL}.
+
 @cindex @code{ffs@var{m}2} instruction pattern
 @item @samp{ffs@var{m}2}
 Store into operand 0 one plus the index of the least significant 1-bit