glsl: Add a constant_referenced method to ir_dereference*

The method is used to get a reference to an ir_constant * within the
context of evaluating an assignment when calculating a
constant_expression_value.

Signed-off-by: Olivier Galibert <galibert@pobox.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net> [v1]

src/glsl/ir.h

@@ -1451,6 +1451,15 @@ public:
     * Get the variable that is ultimately referenced by an r-value
     */
    virtual ir_variable *variable_referenced() const = 0;
+
+   /**
+    * Get the constant that is ultimately referenced by an r-value,
+    * in a constant expression evaluation context.
+    *
+    * The offset is used when the reference is to a specific column of
+    * a matrix.
+    */
+  virtual void constant_referenced(struct hash_table *variable_context, ir_constant *&store, int &offset) const = 0;
 };
 
 
@@ -1476,6 +1485,15 @@ public:
       return this->var;
    }
 
+   /**
+    * Get the constant that is ultimately referenced by an r-value,
+    * in a constant expression evaluation context.
+    *
+    * The offset is used when the reference is to a specific column of
+    * a matrix.
+    */
+   virtual void constant_referenced(struct hash_table *variable_context, ir_constant *&store, int &offset) const;
+
    virtual ir_variable *whole_variable_referenced()
    {
       /* ir_dereference_variable objects always dereference the entire
@@ -1525,6 +1543,15 @@ public:
       return this->array->variable_referenced();
    }
 
+   /**
+    * Get the constant that is ultimately referenced by an r-value,
+    * in a constant expression evaluation context.
+    *
+    * The offset is used when the reference is to a specific column of
+    * a matrix.
+    */
+   virtual void constant_referenced(struct hash_table *variable_context, ir_constant *&store, int &offset) const;
+
    virtual void accept(ir_visitor *v)
    {
       v->visit(this);
@@ -1559,6 +1586,15 @@ public:
       return this->record->variable_referenced();
    }
 
+   /**
+    * Get the constant that is ultimately referenced by an r-value,
+    * in a constant expression evaluation context.
+    *
+    * The offset is used when the reference is to a specific column of
+    * a matrix.
+    */
+   virtual void constant_referenced(struct hash_table *variable_context, ir_constant *&store, int &offset) const;
+
    virtual void accept(ir_visitor *v)
    {
       v->visit(this);

src/glsl/ir_constant_expression.cpp

@@ -923,6 +923,19 @@ ir_swizzle::constant_expression_value(struct hash_table *variable_context)
 }
 
 
+void
+ir_dereference_variable::constant_referenced(struct hash_table *variable_context,
+					     ir_constant *&store, int &offset) const
+{
+   if (variable_context) {
+      store = (ir_constant *)hash_table_find(variable_context, var);
+      offset = 0;
+   } else {
+      store = NULL;
+      offset = 0;
+   }
+}
+
 ir_constant *
 ir_dereference_variable::constant_expression_value(struct hash_table *variable_context)
 {
@@ -950,6 +963,60 @@ ir_dereference_variable::constant_expression_value(struct hash_table *variable_c
 }
 
 
+void
+ir_dereference_array::constant_referenced(struct hash_table *variable_context,
+					  ir_constant *&store, int &offset) const
+{
+   ir_constant *index_c = array_index->constant_expression_value(variable_context);
+
+   if (!index_c || !index_c->type->is_scalar() || !index_c->type->is_integer()) {
+      store = 0;
+      offset = 0;
+      return;
+   }
+
+   int index = index_c->type->base_type == GLSL_TYPE_INT ?
+      index_c->get_int_component(0) :
+      index_c->get_uint_component(0);
+
+   ir_constant *substore;
+   int suboffset;
+   const ir_dereference *deref = array->as_dereference();
+   if (!deref) {
+      store = 0;
+      offset = 0;
+      return;
+   }
+
+   deref->constant_referenced(variable_context, substore, suboffset);
+
+   if (!substore) {
+      store = 0;
+      offset = 0;
+      return;
+   }
+
+   const glsl_type *vt = substore->type;
+   if (vt->is_array()) {
+      store = substore->get_array_element(index);
+      offset = 0;
+      return;
+   }
+   if (vt->is_matrix()) {
+      store = substore;
+      offset = index * vt->vector_elements;
+      return;
+   }
+   if (vt->is_vector()) {
+      store = substore;
+      offset = suboffset + index;
+      return;
+   }
+
+   store = 0;
+   offset = 0;
+}
+
 ir_constant *
 ir_dereference_array::constant_expression_value(struct hash_table *variable_context)
 {
@@ -1005,6 +1072,31 @@ ir_dereference_array::constant_expression_value(struct hash_table *variable_cont
 }
 
 
+void
+ir_dereference_record::constant_referenced(struct hash_table *variable_context,
+					   ir_constant *&store, int &offset) const
+{
+   ir_constant *substore;
+   int suboffset;
+   const ir_dereference *deref = record->as_dereference();
+   if (!deref) {
+      store = 0;
+      offset = 0;
+      return;
+   }
+
+   deref->constant_referenced(variable_context, substore, suboffset);
+
+   if (!substore) {
+      store = 0;
+      offset = 0;
+      return;
+   }
+
+   store = substore->get_record_field(field);
+   offset = 0;
+}
+
 ir_constant *
 ir_dereference_record::constant_expression_value(struct hash_table *variable_context)
 {