Add (void) cast

RFC: https://wiki.php.net/rfc/marking_return_value_as_important

Author: TimWolla

Zend/Optimizer/block_pass.c

@@ -274,7 +274,9 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 				 * If it's not local, then the other blocks successors must also eventually either FREE or consume the temporary,
 				 * hence removing the temporary is not safe in the general case, especially when other consumers are not FREE.
 				 * A FREE may not be removed without also removing the source's result, because otherwise that would cause a memory leak. */
-				if (opline->op1_type == IS_TMP_VAR) {
+				if (opline->extended_value == ZEND_FREE_VOID_CAST) {
+					/* Keep the ZEND_FREE opcode alive. */
+				} else if (opline->op1_type == IS_TMP_VAR) {
 					src = VAR_SOURCE(opline->op1);
 					if (src) {
 						switch (src->opcode) {

Zend/Optimizer/dce.c

@@ -80,7 +80,6 @@ static inline bool may_have_side_effects(
 		case ZEND_IS_IDENTICAL:
 		case ZEND_IS_NOT_IDENTICAL:
 		case ZEND_QM_ASSIGN:
-		case ZEND_FREE:
 		case ZEND_FE_FREE:
 		case ZEND_TYPE_CHECK:
 		case ZEND_DEFINED:
@@ -127,6 +126,8 @@ static inline bool may_have_side_effects(
 		case ZEND_ARRAY_KEY_EXISTS:
 			/* No side effects */
 			return 0;
+		case ZEND_FREE:
+			return opline->extended_value == ZEND_FREE_VOID_CAST;
 		case ZEND_ADD_ARRAY_ELEMENT:
 			/* TODO: We can't free two vars. Keep instruction alive. <?php [0, "$a" => "$b"]; */
 			if ((opline->op1_type & (IS_VAR|IS_TMP_VAR)) && (opline->op2_type & (IS_VAR|IS_TMP_VAR))) {

Zend/tests/type_casts/cast_to_void.phpt

@@ -0,0 +1,47 @@
+--TEST--
+casting different variables to void
+--FILE--
+<?php
+
+$r = fopen(__FILE__, "r");
+
+class test {
+    private $var1 = 1;
+    public $var2 = 2;
+    protected $var3 = 3;
+
+    function  __toString() {
+        return "10";
+    }
+}
+
+$o = new test;
+
+$vars = array(
+    "string",
+    "",
+    "\0",
+    "8754456",
+    9876545,
+    0.10,
+    array(),
+    array(1,2,3),
+    false,
+    true,
+    NULL,
+    $r,
+    $o
+);
+
+foreach ($vars as $var) {
+    (void)$var;
+}
+
+// Cast literals to verify behavior for optimized const zvals
+(void)"foo";
+(void)["foo", "bar"];
+
+echo "Done\n";
+?>
+--EXPECTF--
+Done

Zend/tests/type_casts/cast_to_void_ast.phpt

@@ -0,0 +1,18 @@
+--TEST--
+(void) is included in AST printing
+--FILE--
+<?php
+
+try {
+    assert(false && function () {
+        (void) somefunc();
+    });
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+assert(false && function () {
+    (void)somefunc();
+})

Zend/tests/type_casts/cast_to_void_destructor.phpt

@@ -0,0 +1,30 @@
+--TEST--
+casting to void destroys the value.
+--FILE--
+<?php
+
+class WithDestructor {
+	public function __destruct() {
+		echo __METHOD__, PHP_EOL;
+	}
+}
+
+function test(): WithDestructor {
+	return new WithDestructor();
+}
+
+function do_it(): void {
+	echo "Before", PHP_EOL;
+
+	(void)test();
+
+	echo "After", PHP_EOL;
+}
+
+do_it();
+
+?>
+--EXPECT--
+Before
+WithDestructor::__destruct
+After

Zend/tests/type_casts/cast_to_void_statement.phpt

@@ -0,0 +1,11 @@
+--TEST--
+casting to void is a statement
+--FILE--
+<?php
+
+$tmp = (void)$dummy;
+
+echo "Done\n";
+?>
+--EXPECTF--
+Parse error: syntax error, unexpected token "(void)" in %s on line %d

Zend/zend_ast.c

@@ -2261,6 +2261,9 @@ static ZEND_COLD void zend_ast_export_ex(smart_str *str, zend_ast *ast, int prio
 				EMPTY_SWITCH_DEFAULT_CASE();
 			}
 			break;
+		case ZEND_AST_CAST_VOID:
+			PREFIX_OP("(void)", 240, 241);
+			break;
 		case ZEND_AST_EMPTY:
 			FUNC_OP("empty");
 		case ZEND_AST_ISSET:

Zend/zend_ast.h

@@ -84,6 +84,7 @@ enum _zend_ast_kind {
 	ZEND_AST_UNARY_PLUS,
 	ZEND_AST_UNARY_MINUS,
 	ZEND_AST_CAST,
+	ZEND_AST_CAST_VOID,
 	ZEND_AST_EMPTY,
 	ZEND_AST_ISSET,
 	ZEND_AST_SILENCE,

Zend/zend_compile.c

@@ -10589,6 +10589,26 @@ static void zend_compile_include_or_eval(znode *result, zend_ast *ast) /* {{{ */
 }
 /* }}} */
 
+static void zend_compile_void_cast(znode *result, zend_ast *ast)
+{
+	zend_ast *expr_ast = ast->child[0];
+	znode expr_node;
+	zend_op *opline;
+
+	zend_compile_expr(&expr_node, expr_ast);
+
+	switch (expr_node.op_type) {
+		case IS_TMP_VAR:
+		case IS_VAR:
+			opline = zend_emit_op(NULL, ZEND_FREE, &expr_node, NULL);
+			opline->extended_value = ZEND_FREE_VOID_CAST;
+			break;
+		case IS_CONST:
+			zend_do_free(&expr_node);
+			break;
+	}
+}
+
 static void zend_compile_isset_or_empty(znode *result, zend_ast *ast) /* {{{ */
 {
 	zend_ast *var_ast = ast->child[0];
@@ -11547,6 +11567,9 @@ static void zend_compile_stmt(zend_ast *ast) /* {{{ */
 		case ZEND_AST_THROW:
 			zend_compile_expr(NULL, ast);
 			break;
+		case ZEND_AST_CAST_VOID:
+			zend_compile_void_cast(NULL, ast);
+			break;
 		default:
 		{
 			znode result;

Zend/zend_compile.h

@@ -1092,6 +1092,7 @@ ZEND_API zend_string *zend_type_to_string(zend_type type);
 
 #define ZEND_FREE_ON_RETURN     (1<<0)
 #define ZEND_FREE_SWITCH        (1<<1)
+#define ZEND_FREE_VOID_CAST     (1<<2)
 
 #define ZEND_SEND_BY_VAL     0u
 #define ZEND_SEND_BY_REF     1u