diff --git a/ext/opcache/Optimizer/block_pass.c b/ext/opcache/Optimizer/block_pass.c
index 3f57183ed37..555c2778cfb 100644
--- a/ext/opcache/Optimizer/block_pass.c
+++ b/ext/opcache/Optimizer/block_pass.c
@@ -940,11 +940,8 @@ static void zend_optimize_block(zend_code_block *block, zend_op_array *op_array,
 			}
 
 			VAR_UNSET(opline->op1);
-			if (ZEND_OP1_TYPE(src) == IS_UNUSED) {
-				/* 5.3 may use IS_UNUSED as first argument to ZEND_ADD_... */
+			if (opline->opcode != ZEND_CONCAT) {
 				opline->opcode = ZEND_ADD_STRING;
-			} else {
-				opline->opcode = ZEND_CONCAT;
 			}
 			COPY_NODE(opline->op1, src->op1);
 			old_len = Z_STRLEN(ZEND_OP2_LITERAL(src));
@@ -1039,45 +1036,47 @@ static void zend_optimize_block(zend_code_block *block, zend_op_array *op_array,
 			VAR_UNSET(opline->op1);
 			COPY_NODE(opline->op1, src->op1);
 			MAKE_NOP(src);
-		} else if ((opline->opcode == ZEND_ADD_STRING ||
-				   	opline->opcode == ZEND_ADD_CHAR ||
-				   	opline->opcode == ZEND_ADD_VAR ||
-				   	opline->opcode == ZEND_CONCAT) &&
-				  	ZEND_OP1_TYPE(opline) == IS_TMP_VAR &&
-				  	VAR_SOURCE(opline->op1) &&
-				  	VAR_SOURCE(opline->op1)->opcode == ZEND_CONCAT &&
-				  	ZEND_OP2_TYPE(VAR_SOURCE(opline->op1)) == IS_CONST &&
-				  	Z_TYPE(ZEND_OP2_LITERAL(VAR_SOURCE(opline->op1))) == IS_STRING &&
-				  	Z_STRLEN(ZEND_OP2_LITERAL(VAR_SOURCE(opline->op1))) == 0) {
-			/* convert T = CONCAT(X,''), T = ADD_STRING(T, Y) to T = CONCAT(X,Y) */
-			zend_op *src = VAR_SOURCE(opline->op1);
-			VAR_UNSET(opline->op1);
-			COPY_NODE(opline->op1, src->op1);
-			if (opline->opcode == ZEND_ADD_CHAR) {
-				char c = (char)Z_LVAL(ZEND_OP2_LITERAL(opline));
-				ZVAL_STRINGL(&ZEND_OP2_LITERAL(opline), &c, 1);
+		} else if (opline->opcode == ZEND_CONCAT) {
+			if ((ZEND_OP1_TYPE(opline) & (IS_TMP_VAR|IS_VAR)) &&
+				VAR_SOURCE(opline->op1) &&
+				VAR_SOURCE(opline->op1)->opcode == ZEND_CAST &&
+				VAR_SOURCE(opline->op1)->extended_value == IS_STRING) {
+				/* convert T1 = CAST(STRING, X), T2 = CONCAT(T1, Y) to T2 = CONCAT(X,Y) */
+				zend_op *src = VAR_SOURCE(opline->op1);
+				VAR_UNSET(opline->op1);
+				COPY_NODE(opline->op1, src->op1);
+				MAKE_NOP(src);
 			}
-			opline->opcode = ZEND_CONCAT;
-			literal_dtor(&ZEND_OP2_LITERAL(src)); /* will take care of empty_string too */
-			MAKE_NOP(src);
-		} else if ((opline->opcode == ZEND_ADD_STRING ||
-					opline->opcode == ZEND_ADD_CHAR ||
-					opline->opcode == ZEND_ADD_VAR ||
-					opline->opcode == ZEND_CONCAT) &&
-					(ZEND_OP1_TYPE(opline) & (IS_TMP_VAR|IS_VAR)) &&
-					VAR_SOURCE(opline->op1) &&
-					VAR_SOURCE(opline->op1)->opcode == ZEND_CAST &&
-					VAR_SOURCE(opline->op1)->extended_value == IS_STRING) {
-			/* convert T1 = CAST(STRING, X), T2 = CONCAT(T1, Y) to T2 = CONCAT(X,Y) */
-			zend_op *src = VAR_SOURCE(opline->op1);
-			VAR_UNSET(opline->op1);
-			COPY_NODE(opline->op1, src->op1);
-			if (opline->opcode == ZEND_ADD_CHAR) {
-				char c = (char)Z_LVAL(ZEND_OP2_LITERAL(opline));
-				ZVAL_STRINGL(&ZEND_OP2_LITERAL(opline), &c, 1);
+			if ((ZEND_OP2_TYPE(opline) & (IS_TMP_VAR|IS_VAR)) &&
+				VAR_SOURCE(opline->op2) &&
+				VAR_SOURCE(opline->op2)->opcode == ZEND_CAST &&
+				VAR_SOURCE(opline->op2)->extended_value == IS_STRING) {
+				/* convert T1 = CAST(STRING, X), T2 = CONCAT(Y, T1) to T2 = CONCAT(Y,X) */
+				zend_op *src = VAR_SOURCE(opline->op2);
+				VAR_UNSET(opline->op2);
+				COPY_NODE(opline->op2, src->op1);
+				MAKE_NOP(src);
+			}
+			if (ZEND_OP1_TYPE(opline) == IS_CONST &&
+			    Z_TYPE(ZEND_OP1_LITERAL(opline)) == IS_STRING &&
+			    Z_STRLEN(ZEND_OP1_LITERAL(opline)) == 0) {
+				/* convert CONCAT('', X) => CAST(STRING, X) */
+				literal_dtor(&ZEND_OP1_LITERAL(opline));
+				opline->opcode = ZEND_CAST;
+				opline->extended_value = IS_STRING;
+				COPY_NODE(opline->op1, opline->op2);
+				opline->op2_type = IS_UNUSED;
+				opline->op2.var = 0;
+			} else if (ZEND_OP2_TYPE(opline) == IS_CONST &&
+			           Z_TYPE(ZEND_OP2_LITERAL(opline)) == IS_STRING &&
+			           Z_STRLEN(ZEND_OP2_LITERAL(opline)) == 0) {
+				/* convert CONCAT(X, '') => CAST(STRING, X) */
+				literal_dtor(&ZEND_OP2_LITERAL(opline));
+				opline->opcode = ZEND_CAST;
+				opline->extended_value = IS_STRING;
+				opline->op2_type = IS_UNUSED;
+				opline->op2.var = 0;
 			}
-			opline->opcode = ZEND_CONCAT;
-			MAKE_NOP(src);
 		} else if (opline->opcode == ZEND_QM_ASSIGN &&
 					ZEND_OP1_TYPE(opline) == ZEND_RESULT_TYPE(opline) &&
 					ZEND_OP1(opline).var == ZEND_RESULT(opline).var) {
diff --git a/ext/opcache/Optimizer/pass1_5.c b/ext/opcache/Optimizer/pass1_5.c
index f37084ed79c..031e0e3b375 100644
--- a/ext/opcache/Optimizer/pass1_5.c
+++ b/ext/opcache/Optimizer/pass1_5.c
@@ -87,11 +87,12 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 					break;
 				}
 				EG(error_reporting) = er;
-				literal_dtor(&ZEND_OP1_LITERAL(opline));
-				literal_dtor(&ZEND_OP2_LITERAL(opline));
-				MAKE_NOP(opline);
 
-				zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, tv, &result);
+				if (zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, tv, &result)) {
+					literal_dtor(&ZEND_OP1_LITERAL(opline));
+					literal_dtor(&ZEND_OP2_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			}
 			break;
 
@@ -124,10 +125,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 						break;
 				}
 
-				literal_dtor(&ZEND_OP1_LITERAL(opline));
-				MAKE_NOP(opline);
-
-				zend_optimizer_replace_by_const(op_array, opline + 1, type, tv, &res);
+				if (zend_optimizer_replace_by_const(op_array, opline + 1, type, tv, &res)) {
+					literal_dtor(&ZEND_OP1_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			} else if (opline->extended_value == _IS_BOOL) {
 				/* T = CAST(X, IS_BOOL) => T = BOOL(X) */
 				opline->opcode = ZEND_BOOL;
@@ -151,10 +152,11 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 					break;
 				}
 				EG(error_reporting) = er;
-				literal_dtor(&ZEND_OP1_LITERAL(opline));
-				MAKE_NOP(opline);
 
-				zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, tv, &result);
+				if (zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, tv, &result)) {
+					literal_dtor(&ZEND_OP1_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			}
 			break;
 
@@ -190,6 +192,7 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 				last_op = next_op;
 				final_length += (requires_conversion? 1 : Z_STRLEN(ZEND_OP2_LITERAL(opline)));
 				str = zend_string_alloc(final_length, 0);
+				str->len = final_length;
 				ptr = str->val;
 				ptr[final_length] = '\0';
 				if (requires_conversion) { /* ZEND_ADD_CHAR */
@@ -201,11 +204,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 					ptr++;
 				} else { /* ZEND_ADD_STRING */
 					memcpy(ptr, Z_STRVAL(ZEND_OP2_LITERAL(opline)), Z_STRLEN(ZEND_OP2_LITERAL(opline)));
-					zend_string_release(Z_STR(ZEND_OP2_LITERAL(opline)));
-					Z_STR(ZEND_OP2_LITERAL(opline)) = str;
 					ptr += Z_STRLEN(ZEND_OP2_LITERAL(opline));
+					zend_string_release(Z_STR(ZEND_OP2_LITERAL(opline)));
+					ZVAL_NEW_STR(&ZEND_OP2_LITERAL(opline), str);
 				}
-				Z_STRLEN(ZEND_OP2_LITERAL(opline)) = final_length;
 				next_op = opline + 1;
 				while (next_op < last_op) {
 					if (next_op->opcode == ZEND_ADD_STRING) {
@@ -246,9 +248,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 				if ((offset = zend_get_constant_str("__COMPILER_HALT_OFFSET__", sizeof("__COMPILER_HALT_OFFSET__") - 1)) != NULL) {
 					uint32_t tv = ZEND_RESULT(opline).var;
 
-					literal_dtor(&ZEND_OP2_LITERAL(opline));
-					MAKE_NOP(opline);
-					zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, offset);
+					if (zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, offset)) {
+						literal_dtor(&ZEND_OP2_LITERAL(opline));
+						MAKE_NOP(opline);
+					}
 				}
 				EG(current_execute_data) = orig_execute_data;
 				break;
@@ -269,9 +272,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 				if (Z_TYPE(c) == IS_CONSTANT_AST) {
 					break;
 				}
-				literal_dtor(&ZEND_OP2_LITERAL(opline));
-				MAKE_NOP(opline);
-				zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &c);
+				if (zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &c)) {
+					literal_dtor(&ZEND_OP2_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			}
 
 			/* class constant */
@@ -333,9 +337,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 						} else {
 							MAKE_NOP((opline - 1));
 						}
-						literal_dtor(&ZEND_OP2_LITERAL(opline));
-						MAKE_NOP(opline);
-						zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &t);
+						if (zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &t)) {
+							literal_dtor(&ZEND_OP2_LITERAL(opline));
+							MAKE_NOP(opline);
+						}
 					}
 				}
 			}
@@ -559,9 +564,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 				zval t;
 
 				ZVAL_LONG(&t, Z_STRLEN(ZEND_OP1_LITERAL(opline)));
-				zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, ZEND_RESULT(opline).var, &t);
-				literal_dtor(&ZEND_OP1_LITERAL(opline));
-				MAKE_NOP(opline);
+				if (zend_optimizer_replace_by_const(op_array, opline + 1, IS_TMP_VAR, ZEND_RESULT(opline).var, &t)) {
+					literal_dtor(&ZEND_OP1_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			}
 			break;
 		case ZEND_DEFINED:
@@ -572,9 +578,10 @@ void zend_optimizer_pass1(zend_op_array *op_array, zend_optimizer_ctx *ctx)
 					break;
 				}
 				ZVAL_TRUE(&c);
-				zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &c);
-				literal_dtor(&ZEND_OP1_LITERAL(opline));
-				MAKE_NOP(opline);
+				if (zend_optimizer_replace_by_const(op_array, opline, IS_TMP_VAR, tv, &c)) {
+					literal_dtor(&ZEND_OP1_LITERAL(opline));
+					MAKE_NOP(opline);
+				}
 			}
 			break;
 		case ZEND_DECLARE_CONST:
diff --git a/ext/opcache/Optimizer/zend_optimizer.c b/ext/opcache/Optimizer/zend_optimizer.c
index 7be076cb7f5..d0d67a57dad 100644
--- a/ext/opcache/Optimizer/zend_optimizer.c
+++ b/ext/opcache/Optimizer/zend_optimizer.c
@@ -158,6 +158,9 @@ void zend_optimizer_update_op2_const(zend_op_array *op_array,
 		Z_CACHE_SLOT(op_array->literals[opline->op2.constant]) = op_array->cache_size;
 		op_array->cache_size += sizeof(void*);
 		return;
+	} else if (opline->opcode == ZEND_ADD_VAR) {
+		convert_to_string(val);
+		opline->opcode = ZEND_ADD_STRING;
 	}
 	opline->op2.constant = zend_optimizer_add_literal(op_array, val);
 	if (Z_TYPE_P(val) == IS_STRING) {
@@ -306,6 +309,7 @@ int zend_optimizer_replace_by_const(zend_op_array *op_array,
 				case ZEND_SEND_VAR_NO_REF:
 					if (opline->extended_value & ZEND_ARG_COMPILE_TIME_BOUND) {
 						if (opline->extended_value & ZEND_ARG_SEND_BY_REF) {
+							zval_dtor(val);
 							return 0;
 						}
 						opline->extended_value = 0;
@@ -374,6 +378,7 @@ int zend_optimizer_replace_by_const(zend_op_array *op_array,
 			ZEND_OP2(opline).var == var) {
 			switch (opline->opcode) {
 				case ZEND_ASSIGN_REF:
+					zval_dtor(val);
 					return 0;
 				default:
 					break;