glsl: Add is_basis function

Determines whether it's a basis vector, i.e., a vector with one element
equal to 1 and all other elements equal to 0.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ir.cpp

@@ -46,6 +46,11 @@ bool ir_rvalue::is_negative_one() const
    return false;
 }
 
+bool ir_rvalue::is_basis() const
+{
+   return false;
+}
+
 /**
  * Modify the swizzle make to move one component to another
  *
@@ -1125,6 +1130,49 @@ ir_constant::is_negative_one() const
    return true;
 }
 
+bool
+ir_constant::is_basis() const
+{
+   if (!this->type->is_scalar() && !this->type->is_vector())
+      return false;
+
+   if (this->type->is_boolean())
+      return false;
+
+   unsigned ones = 0;
+   for (unsigned c = 0; c < this->type->vector_elements; c++) {
+      switch (this->type->base_type) {
+      case GLSL_TYPE_FLOAT:
+	 if (this->value.f[c] == 1.0)
+	    ones++;
+	 else if (this->value.f[c] != 0.0)
+	    return false;
+	 break;
+      case GLSL_TYPE_INT:
+	 if (this->value.i[c] == 1)
+	    ones++;
+	 else if (this->value.i[c] != 0)
+	    return false;
+	 break;
+      case GLSL_TYPE_UINT:
+	 if (int(this->value.u[c]) == 1)
+	    ones++;
+	 else if (int(this->value.u[c]) != 0)
+	    return false;
+	 break;
+      default:
+	 /* The only other base types are structures, arrays, samplers, and
+	  * booleans.  Samplers cannot be constants, and the others should
+	  * have been filtered out above.
+	  */
+	 assert(!"Should not get here.");
+	 return false;
+      }
+   }
+
+   return ones == 1;
+}
+
 ir_loop::ir_loop()
 {
    this->ir_type = ir_type_loop;