On Fri, 30 Sep 2022 17:32:34 -0600
Jeff Law <j...@ventanamicro.com> wrote:
> + /* This looks good from a CFG standpoint. Now look at the guts
> + of PRED. Basically we want to verify there are no PHI nodes
> + and no real statements. */
> + if (! gimple_seq_empty_p (phi_nodes (pred)))
> + return false;
So, given the below, neither DEBUG nor labels do count towards an
empty seq [coming in from any PHI that is, otherwise it's a different
thing], which is a bit surprising but well, ok. It looks at PHI IL, so
probably yes. Allegedly that's what it is. Neat if that's true.
> +
> + gimple_stmt_iterator gsi;
> + for (gsi = gsi_last_bb (pred); !gsi_end_p (gsi); gsi_prev (&gsi))
> + {
> + gimple *stmt = gsi_stmt (gsi);
> +
> + switch (gimple_code (stmt))
> + {
> + case GIMPLE_LABEL:
> + if (DECL_NONLOCAL (gimple_label_label (as_a <glabel *> (stmt))))
> + return false;
> + break;
> +
> + case GIMPLE_DEBUG:
> + break;
> +
> + default:
> + return false;
don't like, sounds odd. Are we sure there's no other garbage that can
manifest here? int meow=42;, and meow unused won't survive?, pragmas
neither or stuff ?
> + }
> + }
> +
> + return true;
> +}
> +
> /* We have finished optimizing BB, record any information implied by
> taking a specific outgoing edge from BB. */
>
> @@ -583,6 +656,62 @@ record_edge_info (basic_block bb)
> if (can_infer_simple_equiv && TREE_CODE (inverted) == EQ_EXPR)
> edge_info->record_simple_equiv (op0, op1);
> }
> +
> + /* If this block is a single block loop, then we may be able to
> + record some equivalences on the loop's exit edge. */
> + if (single_block_loop_p (bb))
> + {
> + /* We know it's a single block loop. Now look at the loop
> + exit condition. What we're looking for is whether or not
> + the exit condition is loop invariant which we can detect
> + by checking if all the SSA_NAMEs referenced are defined
> + outside the loop. */
> + if ((TREE_CODE (op0) != SSA_NAME
> + || gimple_bb (SSA_NAME_DEF_STMT (op0)) != bb)
> + && (TREE_CODE (op1) != SSA_NAME
> + || gimple_bb (SSA_NAME_DEF_STMT (op1)) != bb))
> + {
> + /* At this point we know the exit condition is loop
> + invariant. The only way to get out of the loop is
> + if never traverses the backedge to begin with. This
s/if /if it /
> + implies that any PHI nodes create equivalances we can
that any threw me off asking for "that if any". Would have been nicer,
i think?
> + attach to the loop exit edge. */
attach it to
> + int alternative
bool
> + = (EDGE_PRED (bb, 0)->flags & EDGE_DFS_BACK) ? 1 : 0;
> +
> + gphi_iterator gsi;
> + for (gsi = gsi_start_phis (bb);
> + !gsi_end_p (gsi);
> + gsi_next (&gsi))
> + {
> + /* If the other alternative is the same as the result,
> + then this is a degenerate and can be ignored. */
> + if (dst == PHI_ARG_DEF (phi, !alternative))
> + continue;
> +
> + /* Now get the EDGE_INFO class so we can append
> + it to our list. We want the successor edge
> + where the destination is not the source of
> + an incoming edge. */
> + gphi *phi = gsi.phi ();
> + tree src = PHI_ARG_DEF (phi, alternative);
> + tree dst = PHI_RESULT (phi);
> +
> + if (EDGE_SUCC (bb, 0)->dest
> + != EDGE_PRED (bb, !alternative)->src)
by now, alternative would be easier to grok if it would have been spelled
from_backedge_p or something. IMHO.
thanks,
> + edge_info = (class edge_info *)EDGE_SUCC (bb, 0)->aux;
> + else
> + edge_info = (class edge_info *)EDGE_SUCC (bb, 1)->aux;
> +
> + /* Note that since this processing is done independently
> + of other edge equivalency processing, we may not
> + have an EDGE_INFO structure set up yet. */
> + if (edge_info == NULL)
> + edge_info = new class edge_info (false_edge);
> + edge_info->record_simple_equiv (dst, src);
> + }
> + }
> + }
> }
> }
> }
