[PING] Loop-optimizer patches

[Paolo Bonzini]

All these older patches are by Zdenek, but if approved I could take care 
of redoing bootstraps and regtests, and applying them:

http://gcc.gnu.org/ml/gcc-patches/2005-03/msg01611.html
merging of equivalent invariants in rtl level invariant motion

http://gcc.gnu.org/ml/gcc-patches/2005-03/msg02577.html
reenables loop header predictor

http://gcc.gnu.org/ml/gcc/2005-01/msg00059.html
This is for PR19210.  The patch was missing a changelog, so here it is.

	* common.opt (funsafe-loop-optimizations, Wloop-assumptions):
	New flag.
	* loop-iv.c (iv_number_of_iterations): If
	-funsafe-loop-optimizations, assume that no overflows or
	infinite loops occurs with a warning if also -Wloop-assumptions;
	if not, warn if -Wloop-assumptions and gcc cannot optimize a
	loop because of possible overflows or infinite loops.
	* tree-ssa-loop-niter.c (number_of_iterations_cond): Ditto.
	(number_of_iterations_exit): Add a parameter to control
	warnings.
	* tree-ssa-dce.c (find_obviously_necessary_stmts): Assume that
	loops are not infinite if -funsafe-loop-optimizations.
	* doc/invoke.texi (-funsafe-loop-optimizations): Document.
	(-Wloop-assumptions): Document.

Paolo