X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Fcompiler%2Fnir%2Fnir_lower_returns.c;h=e166a7cc32a54dea712756e6940ba0acd0644f44;hb=81e51b412e9fc72000868ebe5bbe2417b1f0486d;hp=cf49d5b09e35d4d5216090e360418aefddf4fb06;hpb=257aa5a1c4a2284ffd43759daa405fc135a40094;p=mesa.git

diff --git a/src/compiler/nir/nir_lower_returns.c b/src/compiler/nir/nir_lower_returns.c
index cf49d5b09e3..e166a7cc32a 100644
--- a/src/compiler/nir/nir_lower_returns.c
+++ b/src/compiler/nir/nir_lower_returns.c
@@ -30,6 +30,15 @@ struct lower_returns_state {
    struct exec_list *cf_list;
    nir_loop *loop;
    nir_variable *return_flag;
+
+   /* This indicates that we have a return which is predicated on some form of
+    * control-flow.  Since whether or not the return happens can only be
+    * determined dynamically at run-time, everything that occurs afterwards
+    * needs to be predicated on the return flag variable.
+    */
+   bool has_predicated_return;
+
+   bool removed_unreachable_code;
 };
 
 static bool lower_returns_in_cf_list(struct exec_list *cf_list,
@@ -82,8 +91,10 @@ lower_returns_in_loop(nir_loop *loop, struct lower_returns_state *state)
     * flag set to true.  We need to predicate everything following the loop
     * on the return flag.
     */
-   if (progress)
+   if (progress) {
       predicate_following(&loop->cf_node, state);
+      state->has_predicated_return = true;
+   }
 
    return progress;
 }
@@ -91,23 +102,48 @@ lower_returns_in_loop(nir_loop *loop, struct lower_returns_state *state)
 static bool
 lower_returns_in_if(nir_if *if_stmt, struct lower_returns_state *state)
 {
-   bool progress;
+   bool progress, then_progress, else_progress;
+
+   bool has_predicated_return = state->has_predicated_return;
+   state->has_predicated_return = false;
 
-   progress = lower_returns_in_cf_list(&if_stmt->then_list, state);
-   progress = lower_returns_in_cf_list(&if_stmt->else_list, state) || progress;
+   then_progress = lower_returns_in_cf_list(&if_stmt->then_list, state);
+   else_progress = lower_returns_in_cf_list(&if_stmt->else_list, state);
+   progress = then_progress || else_progress;
 
    /* If either of the recursive calls made progress, then there were
     * returns inside of the body of the if.  If we're in a loop, then these
     * were lowered to breaks which automatically skip to the end of the
     * loop so we don't have to do anything.  If we're not in a loop, then
-    * all we know is that the return flag is set appropreately and that the
+    * all we know is that the return flag is set appropriately and that the
     * recursive calls ensured that nothing gets executed *inside* the if
     * after a return.  In order to ensure nothing outside gets executed
     * after a return, we need to predicate everything following on the
     * return flag.
     */
-   if (progress && !state->loop)
-      predicate_following(&if_stmt->cf_node, state);
+   if (progress && !state->loop) {
+      if (state->has_predicated_return) {
+         predicate_following(&if_stmt->cf_node, state);
+      } else {
+         /* If there are no nested returns we can just add the instructions to
+          * the end of the branch that doesn't have the return.
+          */
+         nir_cf_list list;
+         nir_cf_extract(&list, nir_after_cf_node(&if_stmt->cf_node),
+                        nir_after_cf_list(state->cf_list));
+
+         if (then_progress && else_progress) {
+            /* Both branches return so delete instructions following the if */
+            nir_cf_delete(&list);
+         } else if (then_progress) {
+            nir_cf_reinsert(&list, nir_after_cf_list(&if_stmt->else_list));
+         } else {
+            nir_cf_reinsert(&list, nir_after_cf_list(&if_stmt->then_list));
+         }
+      }
+   }
+
+   state->has_predicated_return = progress || has_predicated_return;
 
    return progress;
 }
@@ -128,8 +164,9 @@ lower_returns_in_block(nir_block *block, struct lower_returns_state *state)
           */
          return false;
       } else {
+         state->removed_unreachable_code = true;
          nir_cf_delete(&list);
-         return true;
+         return false;
       }
    }
 
@@ -146,6 +183,12 @@ lower_returns_in_block(nir_block *block, struct lower_returns_state *state)
 
    nir_instr_remove(&jump->instr);
 
+   /* If this is a return in the last block of the function there is nothing
+    * more to do once its removed.
+    */
+   if (block == nir_impl_last_block(state->builder.impl))
+      return true;
+
    nir_builder *b = &state->builder;
 
    /* Set the return flag */
@@ -155,11 +198,11 @@ lower_returns_in_block(nir_block *block, struct lower_returns_state *state)
 
       /* Initialize the variable to 0 */
       b->cursor = nir_before_cf_list(&b->impl->body);
-      nir_store_var(b, state->return_flag, nir_imm_int(b, NIR_FALSE), 1);
+      nir_store_var(b, state->return_flag, nir_imm_false(b), 1);
    }
 
    b->cursor = nir_after_block(block);
-   nir_store_var(b, state->return_flag, nir_imm_int(b, NIR_TRUE), 1);
+   nir_store_var(b, state->return_flag, nir_imm_true(b), 1);
 
    if (state->loop) {
       /* We're in a loop;  we need to break out of it. */
@@ -221,13 +264,20 @@ nir_lower_returns_impl(nir_function_impl *impl)
    state.cf_list = &impl->body;
    state.loop = NULL;
    state.return_flag = NULL;
+   state.has_predicated_return = false;
+   state.removed_unreachable_code = false;
    nir_builder_init(&state.builder, impl);
 
    bool progress = lower_returns_in_cf_list(&impl->body, &state);
+   progress = progress || state.removed_unreachable_code;
 
    if (progress) {
       nir_metadata_preserve(impl, nir_metadata_none);
       nir_repair_ssa_impl(impl);
+   } else {
+#ifndef NDEBUG
+      impl->valid_metadata &= ~nir_metadata_not_properly_reset;
+#endif
    }
 
    return progress;