cfgrtl: Fix MEM_EXPR update in duplicate_insn_chain [PR114924]

cfgrtl: Fix MEM_EXPR update in duplicate_insn_chain [PR114924]

The PR shows that when cfgrtl.cc:duplicate_insn_chain attempts to
update the MR_DEPENDENCE_CLIQUE information for a MEM_EXPR we can end up
accidentally dropping (e.g.) an ARRAY_REF from the MEM_EXPR and end up
replacing it with the underlying MEM_REF.  This leads to an
inconsistency in the MEM_EXPR information, and could lead to wrong code.

While the walk down to the MEM_REF is necessary to update
MR_DEPENDENCE_CLIQUE, we should use the outer tree expression for the
MEM_EXPR.  This patch does that.

gcc/ChangeLog:

	PR rtl-optimization/114924
	* cfgrtl.cc (duplicate_insn_chain): When updating MEM_EXPRs,
	don't strip (e.g.) ARRAY_REFs from the final MEM_EXPR.