expansion: Fix ICEs with BLKmode VIEW_CONVERT_EXPR around non-BLKmode VAR_DECLs

expansion: Fix ICEs with BLKmode VIEW_CONVERT_EXPR around non-BLKmode VAR_DECLs

On aarch64 the backend decides to use non-BLKmode for some arrays
like unsigned long[4] - OImode in that case, but the corresponding
BITINT_TYPEs have BLKmode (like structures containing that many limb
elements).
This later causes ICEs durring expansion when expanding VIEW_CONVERT_EXPR
from non-BLKmode VAR_DECL to BLKmode BITINT_TYPE.

The following fix contains two parts, the discover_nonconstant_array_refs_r
is make sure we force such variables into memory and the expand_expr_real_1
change makes sure we don't try to extract a bitfield or something similar
which doesn't really work for BLKmode - as op0 is a MEM, all we need is
the op0 = adjust_address (op0, mode, 0); at the end to change the MEM's mode
to BLKmode.

2024-01-19  Jakub Jelinek  <jakub@redhat.com>
	    Richard Biener  <rguenther@suse.de>

	* cfgexpand.cc (discover_nonconstant_array_refs_r): Force non-BLKmode
	VAR_DECLs referenced in BLKmode VIEW_CONVERT_EXPRs into memory.
	* expr.cc (expand_expr_real_1) <case VIEW_CONVERT_EXPR>: Do nothing
	but adjust_address also for BLKmode mode and MEM op0.