On Tue, Apr 18, 2017 at 12:53 PM, Bin Cheng <bin.ch...@arm.com> wrote:
> Hi,
> Currently IVOPTs shares the same register pressure computation with RTL loop
> invariant pass,
> which doesn't work very well. This patch introduces specific interface for
> IVOPTs.
> The general idea is described in the cover message as below:
> C) Current implementation shares the same register pressure computation
> with RTL loop
> inv pass. It has difficulty in handling (especially large) loop nest,
> and quite
> often generating too many candidates (especially for outer loops). This
> change
> introduces new register pressure computation. The brief idea is to
> differentiate
> (hot) innermost loop and outer loop. for (possibly hot) inner most,
> more registers
> are allowed as long as the register pressure is within the range of
> number of target
> available registers.
> It can also help to restrict number of candidates for outer loop.
> Is it OK?
+/* Determine if current loop is the innermost loop and maybe hot. */
+
+static void
+determine_hot_innermost_loop (struct ivopts_data *data)
+{
+ data->hot_innermost_loop_p = true;
+ if (!data->speed)
+ return;
err, so when not optimizing for speed we assume all loops (even not innermost)
are hot and innermost?!
+ HOST_WIDE_INT niter = avg_loop_niter (loop);
+ if (niter < PARAM_VALUE (PARAM_AVG_LOOP_NITER)
+ || loop_constraint_set_p (loop, LOOP_C_PROLOG)
+ || loop_constraint_set_p (loop, LOOP_C_EPILOG)
+ || loop_constraint_set_p (loop, LOOP_C_VERSION))
+ data->hot_innermost_loop_p = false;
this needs adjustment for the constraint patch removal. Also looking at niter
of the loop in question insn't a good metric for hotness. data->speed is the
best guess you get I think (optimize_loop_for_speed_p).
data->speed = optimize_loop_for_speed_p (loop);
+ determine_hot_innermost_loop (data);
data->hot_innermost_loop_p = determine_hot_innermost_loop (data);
would be more consistent here.
Thanks,
Richard.
> Thanks,
> bin
> 2017-04-11 Bin Cheng <bin.ch...@arm.com>
>
> * tree-ssa-loop-ivopts.c (struct ivopts_data): New field.
> (ivopts_estimate_reg_pressure): New reg_pressure model function.
> (ivopts_global_cost_for_size): Delete.
> (determine_set_costs, iv_ca_recount_cost): Call new model function
> ivopts_estimate_reg_pressure.
> (determine_hot_innermost_loop): New.
> (tree_ssa_iv_optimize_loop): Call above function.
