Don't remove CONST CAST in CONCAT operand

CONCAT assumes that CONST operands are strings, so we cannot
blindly remove CAST operands.

Author: nikic

ext/opcache/Optimizer/block_pass.c

@@ -719,7 +719,8 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 					src = VAR_SOURCE(opline->op1);
 					if (src &&
 					    src->opcode == ZEND_CAST &&
-					    src->extended_value == IS_STRING) {
+					    src->extended_value == IS_STRING &&
+					    src->op1_type != IS_CONST) {
 						/* convert T1 = CAST(STRING, X), T2 = CONCAT(T1, Y) to T2 = CONCAT(X,Y) */
 						VAR_SOURCE(opline->op1) = NULL;
 						COPY_NODE(opline->op1, src->op1);
@@ -731,7 +732,8 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 					src = VAR_SOURCE(opline->op2);
 					if (src &&
 					    src->opcode == ZEND_CAST &&
-					    src->extended_value == IS_STRING) {
+					    src->extended_value == IS_STRING &&
+					    src->op1_type != IS_CONST) {
 						/* convert T1 = CAST(STRING, X), T2 = CONCAT(Y, T1) to T2 = CONCAT(Y,X) */
 						zend_op *src = VAR_SOURCE(opline->op2);
 						VAR_SOURCE(opline->op2) = NULL;