[70/77] Make expand_fix/float check for scalar modes

[70/77] Make expand_fix/float check for scalar modes

The expand_float code:

  /* Unsigned integer, and no way to convert directly.  Convert as signed,
     then unconditionally adjust the result.  */

and the expand_fix code:

  /* For an unsigned conversion, there is one more way to do it.
     If we have a signed conversion, we generate code that compares
     the real value to the largest representable positive number.  If if
     is smaller, the conversion is done normally.  Otherwise, subtract
     one plus the highest signed number, convert, and add it back.

are restricted to scalars, since the expansion branches on a
comparison of the value.  This patch makes that explicit.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* optabs.c (expand_float): Explicitly check for scalars before
	using a branching expansion.
	(expand_fix): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@251521 138bc75d-0d04-0410-961f-82ee72b054a4