glsl: Transform dot product by a basis vector into a swizzle

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

src/glsl/TODO

@@ -6,9 +6,6 @@
   constant index values.  For others it is more complicated.  Perhaps these
   cases should be silently converted to uniforms?
 
-- Implement support for ir_binop_dot in opt_algebraic.cpp.  Perform
-  transformations such as "dot(v, vec3(0.0, 1.0, 0.0))" -> v.y.
-
 - Track source locations throughout the IR.  There are currently several
   places where we cannot emit line numbers for errors (and currently emit 0:0)
   because we've "lost" the line number information.  This is particularly

src/glsl/opt_algebraic.cpp

@@ -84,6 +84,12 @@ is_vec_one(ir_constant *ir)
    return (ir == NULL) ? false : ir->is_one();
 }
 
+static inline bool
+is_vec_basis(ir_constant *ir)
+{
+   return (ir == NULL) ? false : ir->is_basis();
+}
+
 static void
 update_type(ir_expression *ir)
 {
@@ -314,6 +320,24 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
 	 this->progress = true;
 	 return ir_constant::zero(mem_ctx, ir->type);
       }
+      if (is_vec_basis(op_const[0])) {
+	 this->progress = true;
+	 unsigned component = 0;
+	 for (unsigned c = 0; c < op_const[0]->type->vector_elements; c++) {
+	    if (op_const[0]->value.f[c] == 1.0)
+	       component = c;
+	 }
+	 return new(mem_ctx) ir_swizzle(ir->operands[1], component, 0, 0, 0, 1);
+      }
+      if (is_vec_basis(op_const[1])) {
+	 this->progress = true;
+	 unsigned component = 0;
+	 for (unsigned c = 0; c < op_const[1]->type->vector_elements; c++) {
+	    if (op_const[1]->value.f[c] == 1.0)
+	       component = c;
+	 }
+	 return new(mem_ctx) ir_swizzle(ir->operands[0], component, 0, 0, 0, 1);
+      }
       break;
 
    case ir_binop_logic_and: