util/ra: spiff out select_reg_callback

Add a parameter so the callback can know which node it is selecting a
register for.  And remove the graph parameter, as it is unused by
existing users, and somewhat unnecessary (ie. the callback data could
be used instead).

And add a comment so $future_me remembers how this works.

Signed-off-by: Rob Clark <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4071>

2 files changed, 24 insertions, 9 deletions

diff --git a/src/util/register_allocate.c b/src/util/register_allocate.c
index 85453d25290..56517b5161c 100644
--- a/src/util/register_allocate.c
+++ b/src/util/register_allocate.c
@@ -171,8 +171,7 @@ struct ra_graph {
 
    unsigned int alloc; /**< count of nodes allocated. */
 
-   unsigned int (*select_reg_callback)(struct ra_graph *g, BITSET_WORD *regs,
-                                       void *data);
+   ra_select_reg_callback select_reg_callback;
    void *select_reg_callback_data;
 
    /* Temporary data for the algorithm to scratch around in */
@@ -565,9 +564,7 @@ ra_resize_interference_graph(struct ra_graph *g, unsigned int count)
 }
 
 void ra_set_select_reg_callback(struct ra_graph *g,
-                                unsigned int (*callback)(struct ra_graph *g,
-                                                         BITSET_WORD *regs,
-                                                         void *data),
+                                ra_select_reg_callback callback,
                                 void *data)
 {
    g->select_reg_callback = callback;
@@ -868,7 +865,7 @@ ra_select(struct ra_graph *g)
             return false;
          }
 
-         r = g->select_reg_callback(g, select_regs, g->select_reg_callback_data);
+         r = g->select_reg_callback(n, select_regs, g->select_reg_callback_data);
       } else {
          /* Find the lowest-numbered reg which is not used by a member
           * of the graph adjacent to us.
diff --git a/src/util/register_allocate.h b/src/util/register_allocate.h
index fcd4d9394e0..7d8459b1eff 100644
--- a/src/util/register_allocate.h
+++ b/src/util/register_allocate.h
@@ -83,10 +83,28 @@ void ra_resize_interference_graph(struct ra_graph *g, unsigned int count);
 void ra_set_node_class(struct ra_graph *g, unsigned int n, unsigned int c);
 unsigned int ra_get_node_class(struct ra_graph *g, unsigned int n);
 unsigned int ra_add_node(struct ra_graph *g, unsigned int c);
+
+/** @{ Register selection callback.
+ *
+ * The register allocator can use either one of two built-in register
+ * selection behaviors (ie. lowest-available or round-robin), or the
+ * user can implement it's own selection policy by setting an register
+ * selection callback.  The parameters to the callback are:
+ *
+ *  - n       the graph node, ie. the virtual variable to select a
+ *            register for
+ *  - regs    bitset of available registers to choose; this bitset
+ *            contains *all* registers, but registers of different
+ *            classes will not have their corresponding bit set.
+ *  - data    callback data specified in ra_set_select_reg_callback()
+ */
+typedef unsigned int (*ra_select_reg_callback)(
+      unsigned int n,        /* virtual variable to choose a physical reg for */
+      BITSET_WORD *regs,     /* available physical regs to choose from */
+      void *data);
+
 void ra_set_select_reg_callback(struct ra_graph *g,
-                                unsigned int (*callback)(struct ra_graph *g,
-                                                         BITSET_WORD *regs,
-                                                         void *data),
+                                ra_select_reg_callback callback,
                                 void *data);
 void ra_add_node_interference(struct ra_graph *g,
                               unsigned int n1, unsigned int n2);