middle-end/97521 - fix VECTOR_CST expansion

middle-end/97521 - fix VECTOR_CST expansion

This fixes expansion of VECTOR_BOOLEAN_TYPE_P VECTOR_CSTs which
when using an integer mode are not always "mask-mode" but may
be using an integer mode when there's no supported vector mode.

The patch makes sure to only go the mask-mode expansion if
the elements do not line up to cover the full integer mode
(when they do and the mode was an actual mask-mode there's
no actual difference in both expansions).

2020-10-22  Richard Biener  <rguenther@suse.de>

	PR middle-end/97521
	* expr.c (expand_expr_real_1): Be more careful when
	expanding a VECTOR_BOOLEAN_TYPE_P VECTOR_CSTs.

	* gcc.target/i386/pr97521.c: New testcase.