Language: by-reference parameters (VM, #140)

docs/capabilities-syntax.md

@@ -27,6 +27,7 @@ Tracking issues: [#58](https://github.com/PurHur/php-compiler/issues/58), [#145]
 | Magic constant `__LINE__` | yes | yes | yes | [#715](https://github.com/PurHur/php-compiler/issues/715) | Per-site line on TYPE_SCRIPT_MAGIC; include stack for multi-file units; compliance PHPT |
 | Literal `include`/`require` with `__DIR__` | yes | yes | yes | [#475](https://github.com/PurHur/php-compiler/issues/475) | Compile-time inlining via IncludeHelper; two-file PHPT + MiniWebApp JIT gate (#587) |
 | foreach by-reference (`&$v`) | yes | yes | yes | [#1222](https://github.com/PurHur/php-compiler/issues/1222) | Packed and string-keyed arrays; VM + JIT lowering |
+| By-reference parameters (`function f(&$x)`) | yes | no | no | [#140](https://github.com/PurHur/php-compiler/issues/140) | VM aliases caller slots via TYPE_INDIRECT; JIT pointer args deferred; VM-only lowering |
 | Static property `Class::$prop` | yes | yes | yes | [#1225](https://github.com/PurHur/php-compiler/issues/1225) | Class-scoped storage; `self::` / `static::`; literal property names in JIT |
 | `unset()` on variables and array offsets | yes | yes | yes | [#1224](https://github.com/PurHur/php-compiler/issues/1224) | VM + JIT assign null to lvalue slots |
 | Keyed array destructuring (`["a" => $x]`) | yes | yes | yes | [#1234](https://github.com/PurHur/php-compiler/issues/1234) | Skip string-key CFG split for fetch+assign destructuring pairs (#1234) |

lib/Block.php

@@ -76,6 +76,9 @@ class Block {
     /** Declared parameter names by index (issue #168). */
     public array $paramNames = [];
 
+    /** Parameter indices declared with `&$param` (issue #140). */
+    public array $paramByRef = [];
+
     /** Resolved absolute paths for TYPE_INCLUDE opcodes (arg3 index, issue #54). */
     public array $literalIncludePaths = [];
 

lib/Compiler.php

@@ -581,7 +581,9 @@ protected function compileTypeConstrainedVariable(Block $block, Type $type): int
 
 
     protected function compileParam(Op\Expr\Param $param, Block $block, int $paramIdx): OpCode {
-        assert(false === $param->byRef);
+        if ($param->byRef) {
+            $block->paramByRef[$paramIdx] = true;
+        }
         if ($param->variadic) {
             assert(null === $param->defaultVar);
             if (null !== $block->variadicParamIndex) {

lib/VM.php

@@ -556,7 +556,11 @@ private function runFrames(): int
                             $packed->append($copy);
                         }
                     } elseif (array_key_exists($recvIdx, $frame->calledArgs)) {
-                        $arg1->copyFrom($frame->calledArgs[$recvIdx]);
+                        if (isset($frame->block->paramByRef[(int) $op->arg2])) {
+                            $arg1->indirect($frame->calledArgs[$recvIdx]);
+                        } else {
+                            $arg1->copyFrom($frame->calledArgs[$recvIdx]);
+                        }
                     } elseif (null !== $op->arg3 && isset($frame->block->constants[$op->arg3])) {
                         $arg1->copyFrom($frame->block->constants[$op->arg3]);
                     } else {

script/capability-syntax-lib.php

@@ -167,6 +167,16 @@ function syntaxRowDefinitions(): array
             'notes' => ['Packed and string-keyed arrays; VM + JIT lowering'],
             'probe' => '$a = [1, 2, 3]; foreach ($a as &$v) { $v *= 2; } echo $a[0], $a[1], $a[2];',
         ],
+        [
+            'id' => 'ref_param',
+            'construct' => 'By-reference parameters (`function f(&$x)`)',
+            'opcodes' => ['TYPE_ARG_RECV', 'TYPE_ARG_SEND'],
+            'issue' => 140,
+            'jit' => false,
+            'aot' => false,
+            'notes' => ['VM aliases caller slots via TYPE_INDIRECT; JIT pointer args deferred'],
+            'probe' => 'function inc(&$n) { $n++; } $x = 1; inc($x); echo $x;',
+        ],
         [
             'id' => 'static_property_fetch',
             'construct' => 'Static property `Class::$prop`',
@@ -315,9 +325,13 @@ function collectSyntaxCapabilities(string $root, array $definitions, array $hand
         $vm = $opcodeDriven
             ? opcodesSupported($handlers['vm'], $def['opcodes'])
             : (is_string($def['probe']) && $def['probe'] !== '' && probeVmCompile($def['probe']));
-        $jit = $opcodeDriven
-            ? opcodesSupported($handlers['jit'], $def['opcodes'])
-            : $vm;
+        if (array_key_exists('jit', $def)) {
+            $jit = $def['jit'];
+        } else {
+            $jit = $opcodeDriven
+                ? opcodesSupported($handlers['jit'], $def['opcodes'])
+                : $vm;
+        }
         if (array_key_exists('aot', $def)) {
             $aot = $def['aot'];
         } elseif (is_string($def['probe']) && $def['probe'] !== '') {

test/compliance/cases/language/ref_param.phpt

@@ -0,0 +1,19 @@
+--TEST--
+By-reference parameter mutates caller variable (VM, issue #140)
+--FILE--
+<?php
+function inc(&$n) {
+    $n++;
+}
+$x = 1;
+inc($x);
+echo $x, "\n";
+function scale(&$n, $factor) {
+    $n *= $factor;
+}
+$y = 3;
+scale($y, 4);
+echo $y, "\n";
+--EXPECT--
+2
+12