glsl: Improve the local dead code optimization to eliminate unused channels.

Total instructions: 261582 -> 261316
135/2147 programs affected (6.3%)
36752 -> 36486 instructions in affected programs (0.7% reduction)

This excludes a tropics shader that now gets 16-wide mode and throws
off the numbers.  5 shaders are hurt: two extra MOVs in 4 tropics
shaders it looks like because we don't split register names according
to independent webs, and one gstreamer shader where it looks like
try_rewrite_rhs_to_dst() is falling on its face.

This should also help avoid a regression in VSes from idr's ARB
programs to GLSL work.

1 files changed, 126 insertions, 23 deletions

diff --git a/src/glsl/opt_dead_code_local.cpp b/src/glsl/opt_dead_code_local.cpp
index a81a38fff0f..4af78a72cc3 100644
--- a/src/glsl/opt_dead_code_local.cpp
+++ b/src/glsl/opt_dead_code_local.cpp
@@ -43,16 +43,20 @@ static bool debug = false;
 class assignment_entry : public exec_node
 {
 public:
-   assignment_entry(ir_variable *lhs, ir_instruction *ir)
+   assignment_entry(ir_variable *lhs, ir_assignment *ir)
    {
       assert(lhs);
       assert(ir);
       this->lhs = lhs;
       this->ir = ir;
+      this->available = ir->write_mask;
    }
 
    ir_variable *lhs;
-   ir_instruction *ir;
+   ir_assignment *ir;
+
+   /* bitmask of xyzw channels written that haven't been used so far. */
+   int available;
 };
 
 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
@@ -62,23 +66,52 @@ public:
       this->assignments = assignments;
    }
 
-   virtual ir_visitor_status visit(ir_dereference_variable *ir)
+   void kill_channels(ir_variable *const var, int used)
    {
-      ir_variable *const var = ir->variable_referenced();
-
       foreach_iter(exec_list_iterator, iter, *this->assignments) {
 	 assignment_entry *entry = (assignment_entry *)iter.get();
 
 	 if (entry->lhs == var) {
-	    if (debug)
-	       printf("kill %s\n", entry->lhs->name);
-	    entry->remove();
+	    if (var->type->is_scalar() || var->type->is_vector()) {
+	       if (debug)
+		  printf("kill %s (0x%01x - 0x%01x)\n", entry->lhs->name,
+			 entry->available, used);
+	       entry->available &= ~used;
+	       if (!entry->available)
+		  entry->remove();
+	    } else {
+	       if (debug)
+		  printf("kill %s\n", entry->lhs->name);
+	       entry->remove();
+	    }
 	 }
       }
+   }
+
+   virtual ir_visitor_status visit(ir_dereference_variable *ir)
+   {
+      kill_channels(ir->var, ~0);
 
       return visit_continue;
    }
 
+   virtual ir_visitor_status visit(ir_swizzle *ir)
+   {
+      ir_dereference_variable *deref = ir->val->as_dereference_variable();
+      if (!deref)
+	 return visit_continue;
+
+      int used = 0;
+      used |= 1 << ir->mask.x;
+      used |= 1 << ir->mask.y;
+      used |= 1 << ir->mask.z;
+      used |= 1 << ir->mask.w;
+
+      kill_channels(deref->var, used);
+
+      return visit_continue_with_parent;
+   }
+
 private:
    exec_list *assignments;
 };
@@ -130,21 +163,91 @@ process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
    assert(var);
 
    /* Now, check if we did a whole-variable assignment. */
-   if (!ir->condition && (ir->whole_variable_written() != NULL)) {
-      /* We did a whole-variable assignment.  So, any instruction in
-       * the assignment list with the same LHS is dead.
-       */
-      if (debug)
-	 printf("looking for %s to remove\n", var->name);
-      foreach_iter(exec_list_iterator, iter, *assignments) {
-	 assignment_entry *entry = (assignment_entry *)iter.get();
+   if (!ir->condition) {
+      ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
 
-	 if (entry->lhs == var) {
-	    if (debug)
-	       printf("removing %s\n", var->name);
-	    entry->ir->remove();
-	    entry->remove();
-	    progress = true;
+      /* If it's a vector type, we can do per-channel elimination of
+       * use of the RHS.
+       */
+      if (deref_var && (deref_var->var->type->is_scalar() ||
+			deref_var->var->type->is_vector())) {
+
+	 if (debug)
+	    printf("looking for %s.0x%01x to remove\n", var->name,
+		   ir->write_mask);
+
+	 foreach_iter(exec_list_iterator, iter, *assignments) {
+	    assignment_entry *entry = (assignment_entry *)iter.get();
+
+	    if (entry->lhs != var)
+	       continue;
+
+	    int remove = entry->available & ir->write_mask;
+	    if (debug) {
+	       printf("%s 0x%01x - 0x%01x = 0x%01x\n",
+		      var->name,
+		      entry->ir->write_mask,
+		      remove, entry->ir->write_mask & ~remove);
+	    }
+	    if (remove) {
+	       progress = true;
+
+	       if (debug) {
+		  printf("rewriting:\n  ");
+		  entry->ir->print();
+		  printf("\n");
+	       }
+
+	       entry->ir->write_mask &= ~remove;
+	       entry->available &= ~remove;
+	       if (entry->ir->write_mask == 0) {
+		  /* Delete the dead assignment. */
+		  entry->ir->remove();
+		  entry->remove();
+	       } else {
+		  void *mem_ctx = ralloc_parent(entry->ir);
+		  /* Reswizzle the RHS arguments according to the new
+		   * write_mask.
+		   */
+		  unsigned components[4];
+		  unsigned channels = 0;
+		  unsigned next = 0;
+
+		  for (int i = 0; i < 4; i++) {
+		     if ((entry->ir->write_mask | remove) & (1 << i)) {
+			if (!(remove & (1 << i)))
+			   components[channels++] = next;
+			next++;
+		     }
+		  }
+
+		  entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
+							   components,
+							   channels);
+		  if (debug) {
+		     printf("to:\n  ");
+		     entry->ir->print();
+		     printf("\n");
+		  }
+	       }
+	    }
+	 }
+      } else if (ir->whole_variable_written() != NULL) {
+	 /* We did a whole-variable assignment.  So, any instruction in
+	  * the assignment list with the same LHS is dead.
+	  */
+	 if (debug)
+	    printf("looking for %s to remove\n", var->name);
+	 foreach_iter(exec_list_iterator, iter, *assignments) {
+	    assignment_entry *entry = (assignment_entry *)iter.get();
+
+	    if (entry->lhs == var) {
+	       if (debug)
+		  printf("removing %s\n", var->name);
+	       entry->ir->remove();
+	       entry->remove();
+	       progress = true;
+	    }
 	 }
       }
    }
@@ -160,7 +263,7 @@ process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
       foreach_iter(exec_list_iterator, iter, *assignments) {
 	 assignment_entry *entry = (assignment_entry *)iter.get();
 
-	 printf("    %s\n", entry->lhs->name);
+	 printf("    %s (0x%01x)\n", entry->lhs->name, entry->available);
       }
    }