re PR target/77834 (ICE: in make_decl_rtl, at varasm.c:1311 with -O -ftree-pre -mstringop-strategy=libcall)

	PR target/77834
	* dse.c (dse_step5): Call scan_reads even if just
	insn_info->frame_read.  Improve and fix dump file messages.

From-SVN: r241917