nir: rewrite nir_foreach_block and friends

Previously, these were functions which took a callback. This meant that
the per-block code had to be in a separate function, and all the data
that you wanted to pass in had to be a single void *. They walked the
control flow tree recursively, doing a depth-first search, and called
the callback in a preorder, matching the order of the original source
code. But since each node in the control flow tree has a pointer to its
parent, we can implement a "get-next" and "get-previous" method that
does the same thing that the recursive function did with no state at
all. This lets us rewrite nir_foreach_block() as a simple for loop,
which lets us greatly simplify its users in some cases. This does
require us to rewrite every user, although the transformation from the
old nir_foreach_block() to the new nir_foreach_block() is mostly
trivial.

One subtlety, though, is that the new nir_foreach_block() won't handle
the case where the current block is deleted, which the old one could.
There's a new nir_foreach_block_safe() which implements the standard
trick for solving this. Most users don't modify control flow, though, so
they won't need it. Right now, only opt_select_peephole needs it.

The old functions are reimplemented in terms of the new macros, although
they'll go away after everything is converted.

v2: keep an implementation of the old functions around
v3 (Jason Ekstrand): A small cosmetic change and a bugfix in the loop
   handling of nir_cf_node_cf_tree_last().
v4 (Jason Ekstrand): Use the _safe macro in foreach_block_reverse_call

Reviewed-by: Jason Ekstrand <[email protected]>

2 files changed, 202 insertions, 83 deletions

diff --git a/src/compiler/nir/nir.c b/src/compiler/nir/nir.c
index 92bbc378ec1..da016b4bd71 100644
--- a/src/compiler/nir/nir.c
+++ b/src/compiler/nir/nir.c
@@ -1501,109 +1501,143 @@ nir_ssa_def_components_read(nir_ssa_def *def)
    return read_mask;
 }
 
-static bool foreach_cf_node(nir_cf_node *node, nir_foreach_block_cb cb,
-                            bool reverse, void *state);
-
-static inline bool
-foreach_if(nir_if *if_stmt, nir_foreach_block_cb cb, bool reverse, void *state)
+nir_block *
+nir_block_cf_tree_next(nir_block *block)
 {
-   if (reverse) {
-      foreach_list_typed_reverse_safe(nir_cf_node, node, node,
-                                      &if_stmt->else_list) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
+   if (block == NULL) {
+      /* nir_foreach_block_safe() will call this function on a NULL block
+       * after the last iteration, but it won't use the result so just return
+       * NULL here.
+       */
+      return NULL;
+   }
 
-      foreach_list_typed_reverse_safe(nir_cf_node, node, node,
-                                      &if_stmt->then_list) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
-   } else {
-      foreach_list_typed_safe(nir_cf_node, node, node, &if_stmt->then_list) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
+   nir_cf_node *cf_next = nir_cf_node_next(&block->cf_node);
+   if (cf_next)
+      return nir_cf_node_cf_tree_first(cf_next);
 
-      foreach_list_typed_safe(nir_cf_node, node, node, &if_stmt->else_list) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
+   nir_cf_node *parent = block->cf_node.parent;
+
+   switch (parent->type) {
+   case nir_cf_node_if: {
+      /* Are we at the end of the if? Go to the beginning of the else */
+      nir_if *if_stmt = nir_cf_node_as_if(parent);
+      if (&block->cf_node == nir_if_last_then_node(if_stmt))
+         return nir_cf_node_as_block(nir_if_first_else_node(if_stmt));
+
+      assert(&block->cf_node == nir_if_last_else_node(if_stmt));
+      /* fall through */
    }
 
-   return true;
+   case nir_cf_node_loop:
+      return nir_cf_node_as_block(nir_cf_node_next(parent));
+
+   case nir_cf_node_function:
+      return NULL;
+
+   default:
+      unreachable("unknown cf node type");
+   }
 }
 
-static inline bool
-foreach_loop(nir_loop *loop, nir_foreach_block_cb cb, bool reverse, void *state)
+nir_block *
+nir_block_cf_tree_prev(nir_block *block)
 {
-   if (reverse) {
-      foreach_list_typed_reverse_safe(nir_cf_node, node, node, &loop->body) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
-   } else {
-      foreach_list_typed_safe(nir_cf_node, node, node, &loop->body) {
-         if (!foreach_cf_node(node, cb, reverse, state))
-            return false;
-      }
+   if (block == NULL) {
+      /* do this for consistency with nir_block_cf_tree_next() */
+      return NULL;
    }
 
-   return true;
-}
+   nir_cf_node *cf_prev = nir_cf_node_prev(&block->cf_node);
+   if (cf_prev)
+      return nir_cf_node_cf_tree_last(cf_prev);
+
+   nir_cf_node *parent = block->cf_node.parent;
+
+   switch (parent->type) {
+   case nir_cf_node_if: {
+      /* Are we at the beginning of the else? Go to the end of the if */
+      nir_if *if_stmt = nir_cf_node_as_if(parent);
+      if (&block->cf_node == nir_if_first_else_node(if_stmt))
+         return nir_cf_node_as_block(nir_if_last_then_node(if_stmt));
+
+      assert(&block->cf_node == nir_if_first_then_node(if_stmt));
+      /* fall through */
+   }
 
-static bool
-foreach_cf_node(nir_cf_node *node, nir_foreach_block_cb cb,
-                bool reverse, void *state)
-{
-   switch (node->type) {
-   case nir_cf_node_block:
-      return cb(nir_cf_node_as_block(node), state);
-   case nir_cf_node_if:
-      return foreach_if(nir_cf_node_as_if(node), cb, reverse, state);
    case nir_cf_node_loop:
-      return foreach_loop(nir_cf_node_as_loop(node), cb, reverse, state);
-      break;
+      return nir_cf_node_as_block(nir_cf_node_prev(parent));
+
+   case nir_cf_node_function:
+      return NULL;
 
    default:
-      unreachable("Invalid CFG node type");
-      break;
+      unreachable("unknown cf node type");
    }
-
-   return false;
 }
 
-bool
-nir_foreach_block_in_cf_node_call(nir_cf_node *node, nir_foreach_block_cb cb,
-                             void *state)
+nir_block *nir_cf_node_cf_tree_first(nir_cf_node *node)
 {
-   return foreach_cf_node(node, cb, false, state);
-}
+   switch (node->type) {
+   case nir_cf_node_function: {
+      nir_function_impl *impl = nir_cf_node_as_function(node);
+      return nir_start_block(impl);
+   }
 
-bool
-nir_foreach_block_call(nir_function_impl *impl, nir_foreach_block_cb cb, void *state)
-{
-   foreach_list_typed_safe(nir_cf_node, node, node, &impl->body) {
-      if (!foreach_cf_node(node, cb, false, state))
-         return false;
+   case nir_cf_node_if: {
+      nir_if *if_stmt = nir_cf_node_as_if(node);
+      return nir_cf_node_as_block(nir_if_first_then_node(if_stmt));
+   }
+
+   case nir_cf_node_loop: {
+      nir_loop *loop = nir_cf_node_as_loop(node);
+      return nir_cf_node_as_block(nir_loop_first_cf_node(loop));
+   }
+
+   case nir_cf_node_block: {
+      return nir_cf_node_as_block(node);
    }
 
-   return cb(impl->end_block, state);
+   default:
+      unreachable("unknown node type");
+   }
 }
 
-bool
-nir_foreach_block_reverse_call(nir_function_impl *impl, nir_foreach_block_cb cb,
-                          void *state)
+nir_block *nir_cf_node_cf_tree_last(nir_cf_node *node)
 {
-   if (!cb(impl->end_block, state))
-      return false;
+   switch (node->type) {
+   case nir_cf_node_function: {
+      nir_function_impl *impl = nir_cf_node_as_function(node);
+      return nir_impl_last_block(impl);
+   }
 
-   foreach_list_typed_reverse_safe(nir_cf_node, node, node, &impl->body) {
-      if (!foreach_cf_node(node, cb, true, state))
-         return false;
+   case nir_cf_node_if: {
+      nir_if *if_stmt = nir_cf_node_as_if(node);
+      return nir_cf_node_as_block(nir_if_last_else_node(if_stmt));
    }
 
-   return true;
+   case nir_cf_node_loop: {
+      nir_loop *loop = nir_cf_node_as_loop(node);
+      return nir_cf_node_as_block(nir_loop_last_cf_node(loop));
+   }
+
+   case nir_cf_node_block: {
+      return nir_cf_node_as_block(node);
+   }
+
+   default:
+      unreachable("unknown node type");
+   }
+}
+
+nir_block *nir_cf_node_cf_tree_next(nir_cf_node *node)
+{
+   if (node->type == nir_cf_node_block)
+      return nir_cf_node_cf_tree_first(nir_cf_node_next(node));
+   else if (node->type == nir_cf_node_function)
+      return NULL;
+   else
+      return nir_cf_node_as_block(nir_cf_node_next(node));
 }
 
 nir_if *
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index a55e6821cbe..b23130e205b 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -1550,6 +1550,12 @@ nir_start_block(nir_function_impl *impl)
    return (nir_block *) exec_list_get_head(&impl->body);
 }
 
+static inline nir_block *
+nir_impl_last_block(nir_function_impl *impl)
+{
+   return (nir_block *) exec_list_get_tail(&impl->body);
+}
+
 static inline nir_cf_node *
 nir_cf_node_next(nir_cf_node *node)
 {
@@ -2121,14 +2127,93 @@ void nir_ssa_def_rewrite_uses_after(nir_ssa_def *def, nir_src new_src,
 
 uint8_t nir_ssa_def_components_read(nir_ssa_def *def);
 
-/* visits basic blocks in source-code order */
+/*
+ * finds the next basic block in source-code order, returns NULL if there is
+ * none
+ */
+
+nir_block *nir_block_cf_tree_next(nir_block *block);
+
+/* Performs the opposite of nir_block_cf_tree_next() */
+
+nir_block *nir_block_cf_tree_prev(nir_block *block);
+
+/* Gets the first block in a CF node in source-code order */
+
+nir_block *nir_cf_node_cf_tree_first(nir_cf_node *node);
+
+/* Gets the last block in a CF node in source-code order */
+
+nir_block *nir_cf_node_cf_tree_last(nir_cf_node *node);
+
+/* Gets the next block after a CF node in source-code order */
+
+nir_block *nir_cf_node_cf_tree_next(nir_cf_node *node);
+
+/* Macros for loops that visit blocks in source-code order */
+
+#define nir_foreach_block(block, impl) \
+   for (nir_block *block = nir_start_block(impl); block != NULL; \
+        block = nir_block_cf_tree_next(block))
+
+#define nir_foreach_block_safe(block, impl) \
+   for (nir_block *block = nir_start_block(impl), \
+        *next = nir_block_cf_tree_next(block); \
+        block != NULL; \
+        block = next, next = nir_block_cf_tree_next(block))
+
+#define nir_foreach_block_reverse(block, impl) \
+   for (nir_block *block = nir_impl_last_block(impl); block != NULL; \
+        block = nir_block_cf_tree_prev(block))
+
+#define nir_foreach_block_reverse_safe(block, impl) \
+   for (nir_block *block = nir_impl_last_block(impl), \
+        *prev = nir_block_cf_tree_prev(block); \
+        block != NULL; \
+        block = prev, prev = nir_block_cf_tree_prev(block))
+
+#define nir_foreach_block_in_cf_node(block, node) \
+   for (nir_block *block = nir_cf_node_cf_tree_first(node); \
+        block != nir_cf_node_cf_tree_next(node); \
+        block = nir_block_cf_tree_next(block))
+
 typedef bool (*nir_foreach_block_cb)(nir_block *block, void *state);
-bool nir_foreach_block_call(nir_function_impl *impl, nir_foreach_block_cb cb,
-                       void *state);
-bool nir_foreach_block_reverse_call(nir_function_impl *impl, nir_foreach_block_cb cb,
-                               void *state);
-bool nir_foreach_block_in_cf_node_call(nir_cf_node *node, nir_foreach_block_cb cb,
-                                  void *state);
+
+static inline bool
+nir_foreach_block_call(nir_function_impl *impl, nir_foreach_block_cb cb,
+                       void *state)
+{
+   nir_foreach_block_safe(block, impl) {
+      if (!cb(block, state))
+         return false;
+   }
+
+   return true;
+}
+
+static inline bool
+nir_foreach_block_reverse_call(nir_function_impl *impl, nir_foreach_block_cb cb,
+                               void *state)
+{
+   nir_foreach_block_reverse_safe(block, impl) {
+      if (!cb(block, state))
+         return false;
+   }
+
+   return true;
+}
+
+static inline bool
+nir_foreach_block_in_cf_node_call(nir_cf_node *node, nir_foreach_block_cb cb,
+                                  void *state)
+{
+   nir_foreach_block_in_cf_node(block, node) {
+      if (!cb(block, state))
+         return false;
+   }
+
+   return true;
+}
 
 /* If the following CF node is an if, this function returns that if.
  * Otherwise, it returns NULL.