intel/fs/copy-prop: Purge unused ACPs

If the destination of an ACP entry exists only within this block, then
there's no need to keep it for dataflow analysis.  We can delete it from
the out_acp table and avoid growing the bitsets any bigger than we
absolutely have to.  This reduces the maximum number of global ACP
entries in the vs-isnan-dvec with software fp64 on Kaby Lake from 8630
to 3942 and takes the execution time of the piglit vs-isnan-dvec test
from about 1:16.2 on an unoptimized debug build (what we run in CI) with
NIR_VALIDATE=0 to about 56.4 seconds.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs_copy_propagation.cpp

@@ -886,6 +886,25 @@ fs_visitor::opt_copy_propagation()
    foreach_block (block, cfg) {
       progress = opt_copy_propagation_local(copy_prop_ctx, block,
                                             out_acp[block->num]) || progress;
+
+      /* If the destination of an ACP entry exists only within this block,
+       * then there's no need to keep it for dataflow analysis.  We can delete
+       * it from the out_acp table and avoid growing the bitsets any bigger
+       * than we absolutely have to.
+       *
+       * Because nothing in opt_copy_propagation_local touches the block
+       * start/end IPs and opt_copy_propagation_local is incapable of
+       * extending the live range of an ACP destination beyond the block,
+       * it's safe to use the liveness information in this way.
+       */
+      for (unsigned a = 0; a < ACP_HASH_SIZE; a++) {
+         foreach_in_list_safe(acp_entry, entry, &out_acp[block->num][a]) {
+            assert(entry->dst.file == VGRF);
+            if (block->start_ip <= virtual_grf_start[entry->dst.nr] &&
+                virtual_grf_end[entry->dst.nr] <= block->end_ip)
+               entry->remove();
+         }
+      }
    }
 
    /* Do dataflow analysis for those available copies. */