gimple-low: Fix up handling of volatile automatic vars in assume attribute [PR110754]

gimple-low: Fix up handling of volatile automatic vars in assume attribute [PR110754]

As the following testcases show, the gimple-low outlining of assume
magic functions handled volatile automatic vars (including
parameters/results) like non-volatile ones except it copied volatile
to the new PARM_DECL, which has the undesirable effect that a load
from the volatile var is passed to IFN_ASSUME and so there is a
side-effect there even when side-effects of the assume attribute
shouldn't be evaluated.

The following patch fixes that by passing address of the volatile
variables/parameters/results instead and doing loads or stores from it
or to it where it was originally accessed in the assume attribute
expression.

2024-02-10  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/110754
	* gimple-low.cc (assumption_copy_decl): For TREE_THIS_VOLATILE
	decls create PARM_DECL with pointer to original type, set
	TREE_READONLY and keep TREE_THIS_VOLATILE, TREE_ADDRESSABLE,
	DECL_NOT_GIMPLE_REG_P and DECL_BY_REFERENCE cleared.
	(adjust_assumption_stmt_op): For remapped TREE_THIS_VOLATILE decls
	wrap PARM_DECL into a simple TREE_THIS_NO_TRAP MEM_REF.
	(lower_assumption): For TREE_THIS_VOLATILE vars pass ADDR_EXPR
	of the var as argument.

	* gcc.dg/attr-assume-6.c: New test.
	* g++.dg/cpp23/attr-assume12.C: New test.