re PR tree-optimization/53265 (Warn when undefined behavior implies smaller iteration count)

	PR tree-optimization/53265
	* common.opt (Waggressive-loop-optimizations): New option.
	* tree-ssa-loop-niter.c: Include tree-pass.h.
	(do_warn_aggressive_loop_optimizations): New function.
	(record_estimate): Call it.  Don't add !is_exit bounds to loop->bounds
	if number_of_latch_executions returned constant.
	(estimate_numbers_of_iterations_loop): Call number_of_latch_executions
	early.  If number_of_latch_executions returned constant, set
	nb_iterations_upper_bound back to it.
	* cfgloop.h (struct loop): Add warned_aggressive_loop_optimizations
	field.
	* Makefile.in (tree-ssa-loop-niter.o): Depend on $(TREE_PASS_H).
	* doc/invoke.texi (-Wno-aggressive-loop-optimizations): Document.

	* gcc.dg/pr53265.c: New test.
	* gcc.dg/torture/pr49518.c: Add -Wno-aggressive-loop-optimizations
	to dg-options.
	* g++.dg/opt/longbranch2.C (EBCOTLut): Double sizes of a2 and a3
	arrays.
	* gcc.dg/tree-ssa/cunroll-10.c (main): Rename to foo.  Add argument
	n, use it as high bound instead of 4.

	* unwind-dw2.c (execute_cfa_program): Avoid
	-Waggressive-array-optimizations warnings for DW_CFA_GNU_window_save
	on targets with DWARF_FRAME_REGISTERS < 32.

	* testsuite/libmudflap.c/fail37-frag.c: Add optimization barrier.

From-SVN: r196650