Force the selection operand of a GIMPLE COND_EXPR to be a register

Force the selection operand of a GIMPLE COND_EXPR to be a register

This goes away with the selection operand allowed to be a GENERIC
tcc_comparison tree.  It keeps those for vectorizer pattern recog,
those are short lived and removing this instance is a bigger task.

The patch doesn't yet remove dead code and functionality, that's
left for a followup.  Instead the patch makes sure to produce
valid GIMPLE IL and continue to optimize COND_EXPRs where the
previous IL allowed and the new IL showed regressions in the testsuite.

2022-05-16  Richard Biener  <rguenther@suse.de>

	* gimple-expr.cc (is_gimple_condexpr): Equate to is_gimple_val.
	* gimplify.cc (gimplify_pure_cond_expr): Gimplify the condition
	as is_gimple_val.
	* gimple-fold.cc (valid_gimple_rhs_p): Simplify.
	* tree-cfg.cc (verify_gimple_assign_ternary): Likewise.
	* gimple-loop-interchange.cc (loop_cand::undo_simple_reduction):
	Build the condition of the COND_EXPR separately.
	* tree-ssa-loop-im.cc (move_computations_worker): Likewise.
	* tree-vect-generic.cc (expand_vector_condition): Likewise.
	* tree-vect-loop.cc (vect_create_epilog_for_reduction):
	Likewise.
	* vr-values.cc (simplify_using_ranges::simplify): Likewise.
	* tree-vect-patterns.cc: Add comment indicating we are
	building invalid COND_EXPRs and why.
	* omp-expand.cc (expand_omp_simd): Gimplify the condition
	to the COND_EXPR separately.
	(expand_omp_atomic_cas): Note part that should be unreachable
	now.
	* tree-ssa-forwprop.cc (forward_propagate_into_cond): Adjust
	condition for valid replacements.
	* tree-if-conv.cc (predicate_bbs): Simulate previous
	re-folding of the condition in folded COND_EXPRs which
	is necessary because of unfolded GIMPLE_CONDs in the IL
	as in for example gcc.dg/fold-bopcond-1.c.
	* gimple-range-gori.cc (gori_compute::condexpr_adjust):
	Handle that the comparison is now in the def stmt of
	the select operand.  Required by gcc.dg/pr104526.c.

	* gcc.dg/gimplefe-27.c: Adjust.
	* gcc.dg/gimplefe-45.c: Likewise.
	* gcc.dg/pr101145-2.c: Likewise.
	* gcc.dg/pr98211.c: Likewise.
	* gcc.dg/torture/pr89595.c: Likewise.
	* gcc.dg/tree-ssa/divide-7.c: Likewise.
	* gcc.dg/tree-ssa/ssa-lim-12.c: Likewise.