re PR rtl-optimization/20376 (The missed-optimization of general induction variables in the new rtl-level loop optimizer cause performance degradation.)

	PR rtl-optimization/20376
	* toplev.c (process_options): Enable -fweb and -frename-registers when
	unrolling.
	* doc/invoke.texi: Update the information about when -fweb and
	-frename-registers are enabled.

From-SVN: r101961