Elide expand_constructor if move by pieces is preferred

Elide expand_constructor if move by pieces is preferred

Elide expand_constructor when the constructor is static storage and not
mostly zeros and we can move it by pieces prefer to do so since that's
usually more efficient than performing a series of stores from immediates.

2021-05-21  Richard Biener  <rguenther@suse.de>
	    H.J. Lu  <hjl.tools@gmail.com>

gcc/

	PR middle-end/90773
	* expr.c (expand_constructor): Elide expand_constructor if
	move by pieces is preferred.

gcc/testsuite/

	* gcc.target/i386/pr90773-24.c: New test.
	* gcc.target/i386/pr90773-25.c: Likewise.