aarch64: Take issue rate into account for vector loop costs

aarch64: Take issue rate into account for vector loop costs

When SVE is enabled, GCC needs to do a three-way comparison
between scalar, Advanced SIMD and SVE code.  The normal costs
tend to be latency-based, which is well-suited to SLP.  However,
comparing sums of latency costs means that we effectively treat
the code as executing sequentially.  This can hide the effect of
pipeline bubbles or resource contention that in practice are quite
important for loop vectorisation.  This is particularly true for
loops that involve reductions.

This patch therefore tries to estimate how quickly each piece
of code could issue, using a very (very) simplistic model.
It then uses this to adjust the loop vector costs up or down as
appropriate.  Part of the Advanced SIMD vs. SVE adjustment is
opt-in and is not enabled by default even for use_new_vector_costs.

Like with the previous patches, this one only becomes active if
a CPU selects use_new_vector_costs.  It should therefore have
a very low impact on other CPUs.  The code also mostly ignores
CPUs that have no issue information, even if use_new_vector_costs
is enabled for some reason.

gcc/
	* config/aarch64/aarch64.opt
	(-param=aarch64-loop-vect-issue-rate-niters=): New parameter.
	* doc/invoke.texi: Document it.
	* config/aarch64/aarch64-protos.h (aarch64_base_vec_issue_info)
	(aarch64_scalar_vec_issue_info, aarch64_simd_vec_issue_info)
	(aarch64_advsimd_vec_issue_info, aarch64_sve_vec_issue_info)
	(aarch64_vec_issue_info): New structures.
	(cpu_vector_cost): Write comments above the variables rather
	than to the side.
	(cpu_vector_cost::issue_info): New member variable.
	* config/aarch64/aarch64.c: Include gimple-pretty-print.h
	and tree-ssa-loop-niter.h.
	(generic_vector_cost, a64fx_vector_cost, qdf24xx_vector_cost)
	(thunderx_vector_cost, tsv110_vector_cost, cortexa57_vector_cost)
	(exynosm1_vector_cost, xgene1_vector_cost, thunderx2t99_vector_cost)
	(thunderx3t110_vector_cost): Initialize issue_info to null.
	(neoversev1_scalar_issue_info, neoversev1_advsimd_issue_info)
	(neoversev1_sve_issue_info, neoversev1_vec_issue_info): New structures.
	(neoversev1_vector_cost): Use them.
	(aarch64_vec_op_count, aarch64_sve_op_count): New structures.
	(aarch64_vector_costs::saw_sve_only_op): New member variable.
	(aarch64_vector_costs::num_vector_iterations): Likewise.
	(aarch64_vector_costs::scalar_ops): Likewise.
	(aarch64_vector_costs::advsimd_ops): Likewise.
	(aarch64_vector_costs::sve_ops): Likewise.
	(aarch64_vector_costs::seen_loads): Likewise.
	(aarch64_simd_vec_costs_for_flags): New function.
	(aarch64_analyze_loop_vinfo): Initialize num_vector_iterations.
	Count the number of predicate operations required by SVE WHILE
	instructions.
	(aarch64_comparison_type, aarch64_multiply_add_p): New functions.
	(aarch64_sve_only_stmt_p, aarch64_in_loop_reduction_latency): Likewise.
	(aarch64_count_ops): Likewise.
	(aarch64_add_stmt_cost): Record whether see an SVE operation
	that cannot currently be implementing using Advanced SIMD.
	Record issue information about the scalar, Advanced SIMD
	and (where relevant) SVE versions of a loop.
	(aarch64_vec_op_count::dump): New function.
	(aarch64_sve_op_count::dump): Likewise.
	(aarch64_estimate_min_cycles_per_iter): Likewise.
	(aarch64_adjust_body_cost): If issue information is available,
	try to compare the issue rates of the various loop implementations
	and increase or decrease the vector body cost accordingly.