re PR rtl-optimization/54919 (gcc.dg/torture/pr54877.c FAILs with -fvariable-expansion-in-unroller)

gcc/
	PR rtl-optimization/54919
	* loop-unroll.c (struct var_to_expand): Remove accum_pos field.
	(analyze_insn_to_expand_var): Do not record accum_pos.
	(expand_var_during_unrolling): Use validate_replace_rtx_group to
	perform replacement of all references to SET_DEST (set) with the
	new register, including references in REG_EQUAL notes.
	(insert_var_expansion_initialization): Insert initializatio insns
	at the bottom of the pre-header of the loop.

testsuite/
	PR rtl-optimization/54919
	* gcc.dg/pr54919.c: New testcase.

From-SVN: r192439