nir: Add a call to get a struct describing SSA liveness per instruction.

nir-to-tgsi will use this to release release temporaries for SSA storage back to ureg's linear register allocation once they're dead. Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3395>
2020-07-22 09:06:48 -07:00
parent a206b58157
commit c730feacc0
2 changed files with 95 additions and 0 deletions
@@ -286,3 +286,78 @@ nir_ssa_defs_interfere(nir_ssa_def *a, nir_ssa_def *b)
      return nir_ssa_def_is_live_at(b, a->parent_instr);
   }
 }
+
+/* Takes an SSA def's defs and uses and expands the live interval to cover
+ * that range.  Control flow effects are handled separately.
+ */
+static bool def_cb(nir_ssa_def *def, void *state)
+{
+   nir_instr_liveness *liveness = state;
+   nir_instr *instr = def->parent_instr;
+   int index = def->index;
+
+   liveness->defs[index].start = MIN2(liveness->defs[index].start, instr->index);
+
+   nir_foreach_use(src, def) {
+      liveness->defs[index].end = MAX2(liveness->defs[index].end,
+                                       src->parent_instr->index);
+   }
+
+   return true;
+}
+
+nir_instr_liveness *
+nir_live_ssa_defs_per_instr(nir_function_impl *impl)
+{
+   /* We'll use block-level live_ssa_defs to expand our per-instr ranges for
+    * control flow.
+    */
+   nir_metadata_require(impl,
+                        nir_metadata_block_index |
+                        nir_metadata_instr_index |
+                        nir_metadata_live_ssa_defs);
+
+   /* Make our struct. */
+   nir_instr_liveness *liveness = ralloc(NULL, nir_instr_liveness);
+   liveness->defs = rzalloc_array(liveness, nir_liveness_bounds,
+                                  impl->ssa_alloc);
+
+   /* Set our starts so we can use MIN2() as we accumulate bounds. */
+   for (int i = 0; i < impl->ssa_alloc; i++)
+      liveness->defs->start = ~0;
+
+   unsigned last_instr = 0;
+   nir_foreach_block(block, impl) {
+      unsigned index;
+      BITSET_FOREACH_SET(index, block->live_in, impl->ssa_alloc) {
+         liveness->defs[index].start = MIN2(liveness->defs[index].start,
+                                            last_instr);
+      }
+
+      nir_foreach_instr(instr, block) {
+         nir_foreach_ssa_def(instr, def_cb, liveness);
+
+         last_instr = instr->index;
+      };
+
+      /* track an if src's use.  We need to make sure that our value is live
+       * across the if reference, where we don't have an instr->index
+       * representing the use.  Mark it as live through the next real
+       * instruction.
+       */
+      nir_if *nif = nir_block_get_following_if(block);
+      if (nif) {
+         if (nif->condition.is_ssa) {
+            liveness->defs[nif->condition.ssa->index].end = MAX2(
+               liveness->defs[nif->condition.ssa->index].end,
+               last_instr + 1);
+         }
+      }
+
+      BITSET_FOREACH_SET(index, block->live_out, impl->ssa_alloc) {
+         liveness->defs[index].end = MAX2(liveness->defs[index].end, last_instr);
+      }
+   }
+
+   return liveness;
+}