glsl: Add ir_rvalue::is_negative_one predicate

src/glsl/ir.cpp

@@ -41,6 +41,11 @@ bool ir_rvalue::is_one() const
    return false;
 }
 
+bool ir_rvalue::is_negative_one() const
+{
+   return false;
+}
+
 /**
  * Modify the swizzle make to move one component to another
  *
@@ -764,6 +769,42 @@ ir_constant::is_one() const
    return true;
 }
 
+bool
+ir_constant::is_negative_one() const
+{
+   if (!this->type->is_scalar() && !this->type->is_vector())
+      return false;
+
+   if (this->type->is_boolean())
+      return false;
+
+   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)
+	    return false;
+	 break;
+      case GLSL_TYPE_INT:
+	 if (this->value.i[c] != -1)
+	    return false;
+	 break;
+      case GLSL_TYPE_UINT:
+	 if (int(this->value.u[c]) != -1)
+	    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 true;
+}
+
 ir_loop::ir_loop()
 {
    this->ir_type = ir_type_loop;

src/glsl/ir.h

@@ -179,7 +179,7 @@ public:
     * for vector and scalar types that have all elements set to the value
     * zero (or \c false for booleans).
     *
-    * \sa ir_constant::has_value, ir_rvalue::is_one
+    * \sa ir_constant::has_value, ir_rvalue::is_one, ir_rvalue::is_negative_one
     */
    virtual bool is_zero() const;
 
@@ -191,10 +191,22 @@ public:
     * for vector and scalar types that have all elements set to the value
     * one (or \c true for booleans).
     *
-    * \sa ir_constant::has_value, ir_rvalue::is_zero
+    * \sa ir_constant::has_value, ir_rvalue::is_zero, ir_rvalue::is_negative_one
     */
    virtual bool is_one() const;
 
+   /**
+    * Determine if an r-value has the value negative one
+    *
+    * The base implementation of this function always returns \c false.  The
+    * \c ir_constant class over-rides this function to return \c true \b only
+    * for vector and scalar types that have all elements set to the value
+    * negative one.  For boolean times, the result is always \c false.
+    *
+    * \sa ir_constant::has_value, ir_rvalue::is_zero, ir_rvalue::is_one
+    */
+   virtual bool is_negative_one() const;
+
 protected:
    ir_rvalue();
 };
@@ -1482,12 +1494,14 @@ public:
    /**
     * Determine whether a constant has the same value as another constant
     *
-    * \sa ir_constant::is_zero, ir_constant::is_one
+    * \sa ir_constant::is_zero, ir_constant::is_one,
+    * ir_constant::is_negative_one
     */
    bool has_value(const ir_constant *) const;
 
    virtual bool is_zero() const;
    virtual bool is_one() const;
+   virtual bool is_negative_one() const;
 
    /**
     * Value of the constant.