glsl: remove dead code in a single pass

Currently only one ir assignment is removed for each var in a single
dead code optimisation pass. This means if a var has more than one
assignment, then it requires all the glsl optimisations to be run again
for each additional assignment to be removed.
Another pass is also required to remove the variable itself.

With this change all assignments and the variable are removed in a single
pass.

Some of the arrays of arrays conformance tests that were looping
through 8 dimensions ended up with a var with hundreds of assignments.

This change helps ES31-CTS.arrays_of_arrays.InteractionFunctionCalls1
go from around 3 min 20 sec -> 2 min

ES31-CTS.arrays_of_arrays.InteractionFunctionCalls2 went from
around 9 min 20 sec to 7 min 30 sec

I had difficulty getting the public shader-db to give a consistent result
with or without this change but the results seemed unchanged at between
15-20 seconds.

Thomas Helland measured change with shader-db on his machine from
approx 117 secs to 112 secs.

V3: Simplify freeing of list as suggested by Ian, and spelling fixes.

V2: Add assert to be sure references are counted before assignments.

Reviewed-by: Ian Romanick <[email protected]>
Tested-By: Thomas Helland <[email protected]>
Tested-by: Ian Romanick <[email protected]>

1 files changed, 23 insertions, 3 deletions

diff --git a/src/glsl/ir_variable_refcount.cpp b/src/glsl/ir_variable_refcount.cpp
index e4d825c454b..790627bd1e3 100644
--- a/src/glsl/ir_variable_refcount.cpp
+++ b/src/glsl/ir_variable_refcount.cpp
@@ -46,6 +46,15 @@ static void
 free_entry(struct hash_entry *entry)
 {
    ir_variable_refcount_entry *ivre = (ir_variable_refcount_entry *) entry->data;
+
+   /* Free assignment list */
+   exec_node *n;
+   while ((n = ivre->assign_list.pop_head()) != NULL) {
+      struct assignment_entry *assignment_entry =
+         exec_node_data(struct assignment_entry, n, link);
+      free(assignment_entry);
+   }
+
    delete ivre;
 }
 
@@ -59,7 +68,6 @@ ir_variable_refcount_visitor::~ir_variable_refcount_visitor()
 ir_variable_refcount_entry::ir_variable_refcount_entry(ir_variable *var)
 {
    this->var = var;
-   assign = NULL;
    assigned_count = 0;
    declaration = false;
    referenced_count = 0;
@@ -125,8 +133,20 @@ ir_variable_refcount_visitor::visit_leave(ir_assignment *ir)
    entry = this->get_variable_entry(ir->lhs->variable_referenced());
    if (entry) {
       entry->assigned_count++;
-      if (entry->assign == NULL)
-	 entry->assign = ir;
+
+      /* Build a list for dead code optimisation. Don't add assignment if it
+       * was declared out of scope (outside the instruction stream). Also don't
+       * bother adding any more to the list if there are more references than
+       * assignments as this means the variable is used and won't be optimised
+       * out.
+       */
+      assert(entry->referenced_count >= entry->assigned_count);
+      if (entry->referenced_count == entry->assigned_count) {
+         struct assignment_entry *assignment_entry =
+            (struct assignment_entry *)calloc(1, sizeof(*assignment_entry));
+         assignment_entry->assign = ir;
+         entry->assign_list.push_head(&assignment_entry->link);
+      }
    }
 
    return visit_continue;