Check if instruction may throw exception only for instructions without known side effects.

Always disable removing ASSIGN and UNSET_VAR that may throw.

ext/opcache/Optimizer/dce.c

@@ -69,13 +69,9 @@ static inline zend_bool is_bad_mod(const zend_ssa *ssa, int use, int def) {
 }
 
 static inline zend_bool may_have_side_effects(
-		const context *ctx, const zend_op *opline, const zend_ssa_op *ssa_op) {
-	zend_op_array *op_array = ctx->op_array;
-	zend_ssa *ssa = ctx->ssa;
-	if (zend_may_throw(opline, op_array, ssa)) {
-		return 1;
-	}
-
+		zend_op_array *op_array, zend_ssa *ssa,
+		const zend_op *opline, const zend_ssa_op *ssa_op,
+		zend_bool reorder_dtor_effects) {
 	switch (opline->opcode) {
 		case ZEND_NOP:
 		case ZEND_IS_IDENTICAL:
@@ -154,15 +150,10 @@ static inline zend_bool may_have_side_effects(
 			return 1;
 		case ZEND_ASSIGN:
 		{
-			uint32_t t1 = OP1_INFO();
 			if (is_bad_mod(ssa, ssa_op->op1_use, ssa_op->op1_def)) {
 				return 1;
 			}
-			if (!ctx->reorder_dtor_effects) {
-				if (t1 & MAY_HAVE_DTOR) {
-					/* DCE might extend lifetime */
-					return 1;
-				}
+			if (!reorder_dtor_effects) {
 				if (opline->op2_type != IS_CONST && (OP2_INFO() & MAY_HAVE_DTOR)) {
 					/* DCE might shorten lifetime */
 					return 1;
@@ -183,10 +174,6 @@ static inline zend_bool may_have_side_effects(
 				 * is a reference, because unset breaks references. */
 				return 1;
 			}
-			if (!ctx->reorder_dtor_effects && (t1 & MAY_HAVE_DTOR)) {
-				/* DCE might extend lifetime */
-				return 1;
-			}
 			return 0;
 		}
 		case ZEND_PRE_INC:
@@ -481,7 +468,9 @@ int dce_optimize_op_array(zend_op_array *op_array, zend_ssa *ssa, zend_bool reor
 
 	/* Mark instruction with side effects as live */
 	FOREACH_INSTR_NUM(i) {
-		if (may_have_side_effects(&ctx, &op_array->opcodes[i], &ssa->ops[i]) || has_varargs) {
+		if (may_have_side_effects(op_array, ssa, &op_array->opcodes[i], &ssa->ops[i], ctx.reorder_dtor_effects)
+				|| zend_may_throw(&op_array->opcodes[i], op_array, ssa)
+				|| has_varargs) {
 			zend_bitset_excl(ctx.instr_dead, i);
 			add_operands_to_worklists(&ctx, &op_array->opcodes[i], &ssa->ops[i]);
 		}

ext/opcache/Optimizer/zend_inference.c

@@ -4024,6 +4024,7 @@ int zend_may_throw(const zend_op *opline, zend_op_array *op_array, zend_ssa *ssa
 		case ZEND_COALESCE:
 		case ZEND_SWITCH_LONG:
 		case ZEND_SWITCH_STRING:
+		case ZEND_ISSET_ISEMPTY_VAR:
 			return 0;
 		case ZEND_INIT_FCALL:
 			/* can't throw, because call is resolved at compile time */
@@ -4157,6 +4158,7 @@ int zend_may_throw(const zend_op *opline, zend_op_array *op_array, zend_ssa *ssa
 			return (t1 & (MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT)) ||
 				(t2 & (MAY_BE_STRING|MAY_BE_ARRAY|MAY_BE_OBJECT));
 		case ZEND_ASSIGN:
+		case ZEND_UNSET_VAR:
 			return (t1 & (MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_ARRAY_OF_OBJECT|MAY_BE_ARRAY_OF_RESOURCE|MAY_BE_ARRAY_OF_ARRAY));
 		case ZEND_ASSIGN_DIM:
 			return (t1 & (MAY_BE_OBJECT|MAY_BE_RESOURCE|MAY_BE_TRUE|MAY_BE_STRING|MAY_BE_LONG|MAY_BE_DOUBLE)) || opline->op2_type == IS_UNUSED ||