Add ir_constant_expression.cpp support for <, >, <=, >=.

This results in folding one more constant expression in CorrectParse2.frag.
diff --git a/ir_constant_expression.cpp b/ir_constant_expression.cpp
index 69a3613..f90c69b 100644
--- a/ir_constant_expression.cpp
+++ b/ir_constant_expression.cpp
@@ -252,6 +252,72 @@
       for (c = 0; c < ir->operands[0]->type->components(); c++)
 	 b[c] = op[0]->value.b[c] || op[1]->value.b[c];
       break;
+
+   case ir_binop_less:
+      type = glsl_type::bool_type;
+      switch (ir->operands[0]->type->base_type) {
+      case GLSL_TYPE_UINT:
+	 b[0] = op[0]->value.u[0] < op[1]->value.u[0];
+	 break;
+      case GLSL_TYPE_INT:
+	 b[0] = op[0]->value.i[0] < op[1]->value.i[0];
+	 break;
+      case GLSL_TYPE_FLOAT:
+	 b[0] = op[0]->value.f[0] < op[1]->value.f[0];
+	 break;
+      default:
+	 assert(0);
+      }
+      break;
+   case ir_binop_greater:
+      type = glsl_type::bool_type;
+      switch (ir->operands[0]->type->base_type) {
+      case GLSL_TYPE_UINT:
+	 b[0] = op[0]->value.u[0] > op[1]->value.u[0];
+	 break;
+      case GLSL_TYPE_INT:
+	 b[0] = op[0]->value.i[0] > op[1]->value.i[0];
+	 break;
+      case GLSL_TYPE_FLOAT:
+	 b[0] = op[0]->value.f[0] > op[1]->value.f[0];
+	 break;
+      default:
+	 assert(0);
+      }
+      break;
+   case ir_binop_lequal:
+      type = glsl_type::bool_type;
+      switch (ir->operands[0]->type->base_type) {
+      case GLSL_TYPE_UINT:
+	 b[0] = op[0]->value.u[0] <= op[1]->value.u[0];
+	 break;
+      case GLSL_TYPE_INT:
+	 b[0] = op[0]->value.i[0] <= op[1]->value.i[0];
+	 break;
+      case GLSL_TYPE_FLOAT:
+	 b[0] = op[0]->value.f[0] <= op[1]->value.f[0];
+	 break;
+      default:
+	 assert(0);
+      }
+      break;
+   case ir_binop_gequal:
+      type = glsl_type::bool_type;
+      switch (ir->operands[0]->type->base_type) {
+      case GLSL_TYPE_UINT:
+	 b[0] = op[0]->value.u[0] >= op[1]->value.u[0];
+	 break;
+      case GLSL_TYPE_INT:
+	 b[0] = op[0]->value.i[0] >= op[1]->value.i[0];
+	 break;
+      case GLSL_TYPE_FLOAT:
+	 b[0] = op[0]->value.f[0] >= op[1]->value.f[0];
+	 break;
+      default:
+	 assert(0);
+      }
+      break;
+
    default:
       break;
    }