RISC-V: Move RVV V_REGS liveness computation into analyze_loop_vinfo

RISC-V: Move RVV V_REGS liveness computation into analyze_loop_vinfo

Currently, we compute RVV V_REGS liveness during better_main_loop_than_p which is not appropriate
time to do that since we for example, when have the codes will finally pick LMUL = 8 vectorization
factor, we compute liveness for LMUL = 8 multiple times which are redundant.

Since we have leverage the current ARM SVE COST model:

  /* Do one-time initialization based on the vinfo.  */
  loop_vec_info loop_vinfo = dyn_cast<loop_vec_info> (m_vinfo);
  if (!m_analyzed_vinfo)
    {
      if (loop_vinfo)
	analyze_loop_vinfo (loop_vinfo);

      m_analyzed_vinfo = true;
    }

Analyze COST model only once for each cost model.

So here we move dynamic LMUL liveness information into analyze_loop_vinfo.

/* Do one-time initialization of the costs given that we're
   costing the loop vectorization described by LOOP_VINFO.  */
void
costs::analyze_loop_vinfo (loop_vec_info loop_vinfo)
{
  ...

  /* Detect whether the LOOP has unexpected spills.  */
  record_potential_unexpected_spills (loop_vinfo);
}

So that we can avoid redundant computations and the current dynamic LMUL cost model flow is much
more reasonable and consistent with others.

Tested on RV32 and RV64 no regressions.

gcc/ChangeLog:

	* config/riscv/riscv-vector-costs.cc (compute_estimated_lmul): Allow
	fractional vecrtor.
	(preferred_new_lmul_p): Move RVV V_REGS liveness computation into analyze_loop_vinfo.
	(has_unexpected_spills_p): New function.
	(costs::record_potential_unexpected_spills): Ditto.
	(costs::better_main_loop_than_p): Move RVV V_REGS liveness computation into
	analyze_loop_vinfo.
	* config/riscv/riscv-vector-costs.h: New functions and variables.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul-mixed-1.c: Robostify test.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul1-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul2-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-10.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul4-8.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-10.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-11.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-2.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-3.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-4.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-5.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-6.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-7.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-8.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-9.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/no-dynamic-lmul-1.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/pr111848.c: Ditto.
	* gcc.dg/vect/costmodel/riscv/rvv/pr113112-1.c: Ditto.