Add flag -ftree-loop-if-convert-stores.

Add flag -ftree-loop-if-convert-stores.

This patch adds a flag that controls the replacement of the memory
writes that are in predicated basic blocks with a full write:

for (...)
  if (cond)
    A[i] = foo

is replaced with:

for (...)
  A[i] = cond ? foo : A[i]

In order to do this, we have to call gimple_could_trap_p instead of
gimple_assign_rhs_could_trap_p, as we have to also check that the LHS
of assign stmts does not trap.

	* common.opt (ftree-loop-if-convert-stores): New flag.
	* doc/invoke.texi (ftree-loop-if-convert-stores): Documented.
	* tree-if-conv.c (ifc_temp_var): Pass an extra parameter GSI.  Insert
	the created statement before GSI.
	(if_convertible_phi_p): Allow virtual phi nodes when
	flag_loop_if_convert_stores is set.
	(if_convertible_gimple_assign_stmt_p): Allow memory reads and writes
	Do not handle types that do not match is_gimple_reg_type.
	Remove loop and bb parameters.  Call gimple_could_trap_p instead of
	when flag_loop_if_convert_stores is set, as LHS can contain
	memory refs.
	(if_convertible_stmt_p): Remove loop and bb parameters.  Update calls
	to if_convertible_gimple_assign_stmt_p.
	(if_convertible_loop_p): Update call to if_convertible_stmt_p.
	(replace_phi_with_cond_gimple_assign_stmt): Renamed
	predicate_scalar_phi.  Do not handle virtual phi nodes.
	(ifconvert_phi_nodes): Renamed predicate_all_scalar_phis.
	Call predicate_scalar_phi.
	(insert_gimplified_predicates): Insert the gimplified predicate of a BB
	just after the labels for flag_loop_if_convert_stores, otherwise
	insert the predicate in the end of the BB.
	(predicate_mem_writes): New.
	(combine_blocks): Call predicate_all_scalar_phis.  When
	flag_loop_if_convert_stores is set, call predicate_mem_writes.
	(tree_if_conversion): Call mark_sym_for_renaming when
	flag_loop_if_convert_stores is set.
	(main_tree_if_conversion): Return TODO_update_ssa_only_virtuals when
	flag_loop_if_convert_stores is set.

	* gcc.dg/tree-ssa/ifc-4.c: New.
	* gcc.dg/tree-ssa/ifc-7.c: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@163530 138bc75d-0d04-0410-961f-82ee72b054a4