We didn't take the cost of generating loop masks into account, and so
tended to underestimate the cost of loops that need multiple masks.

2019-11-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-loop.c (vect_estimate_min_profitable_iters): Include
	the cost of generating loop masks.

gcc/testsuite/
	* gcc.target/aarch64/sve/mask_struct_store_3.c: Add
	-fno-vect-cost-model.
	* gcc.target/aarch64/sve/mask_struct_store_3_run.c: Likewise.
	* gcc.target/aarch64/sve/peel_ind_2.c: Likewise.
	* gcc.target/aarch64/sve/peel_ind_2_run.c: Likewise.
	* gcc.target/aarch64/sve/peel_ind_3.c: Likewise.
	* gcc.target/aarch64/sve/peel_ind_3_run.c: Likewise.

From-SVN: r278125