cd_dce: Return TODO_update_address_taken from last cd_dce [PR96271]

cd_dce: Return TODO_update_address_taken from last cd_dce [PR96271]

On the following testcase, handle_builtin_memcmp in the strlen pass folds
the memcmp into comparison of two MEM_REFs.  But nothing triggers updating
of addressable vars afterwards, so even when the parameters are no longer
address taken, we force the parameters to stack and back anyway.

This patch causes TODO_update_address_taken to happen right before last forwprop
pass (at the end of last cd_dce), so after strlen1 too.

2021-01-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96271
	* passes.def: Pass false argument to first two pass_cd_dce
	instances and true to last instance.  Add comment that
	last instance rewrites no longer addressed locals.
	* tree-ssa-dce.c (pass_cd_dce): Add update_address_taken_p member and
	initialize it.
	(pass_cd_dce::set_pass_param): New method.
	(pass_cd_dce::execute): Return TODO_update_address_taken from
	last cd_dce instance.

	* gcc.target/i386/pr96271.c: New test.