WIP: trait __construct MCJIT blocked by DECLARE_TRAIT link segfault (#4939)

test/repro/trait_empty_mcjit_probe.php

@@ -0,0 +1,3 @@
+<?php
+trait T {}
+echo "ok\n";

test/unit/TraitConstructorJitExecuteTest.php

@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler;
+
+use PHPUnit\Framework\TestCase;
+
+require_once __DIR__.'/../LlvmToolchain.php';
+
+/**
+ * MCJIT execute for trait-merged __construct (#4939, Zend/zend_traits.c).
+ *
+ * Blocked: any script with TYPE_DECLARE_TRAIT segfaults in MCJIT createJITCompiler
+ * (repro: `php bin/jit.php -l test/repro/trait_empty.php` → exit 139). VM fallback via
+ * Block::containsTraitConstructorOpcodes() remains required until DECLARE_TRAIT MCJIT is stable (#3609).
+ *
+ * @group llvm
+ */
+final class TraitConstructorJitExecuteTest extends TestCase
+{
+    private string $repoRoot;
+
+    protected function setUp(): void
+    {
+        $this->repoRoot = dirname(__DIR__, 2);
+        LlvmToolchain::applyCurrentProcessEnv($this->repoRoot);
+        if (!LlvmToolchain::isReady($this->repoRoot)) {
+            $reason = LlvmToolchain::readyFailureReason() ?? 'LLVM 9 toolchain not available';
+            $this->markTestSkipped($reason.' — trait constructor JIT execute needs LLVM (#4939)');
+        }
+        if (!$this->jitRuntimeProbeGreen()) {
+            $this->markTestSkipped('jit-runtime-probe failed — MCJIT execute unavailable (#4939)');
+        }
+        if ($this->declareTraitMcjitLinkSegfaults()) {
+            $this->markTestSkipped(
+                'TYPE_DECLARE_TRAIT MCJIT link segfault — remove containsTraitConstructorOpcodes gate after #3609 (#4939)'
+            );
+        }
+    }
+
+    public function testTraitPromotedConstructorViaMcjit(): void
+    {
+        $this->assertMcjitOutput(<<<'PHP'
+<?php
+trait HasX {
+    public function __construct(public int $x) {}
+}
+class C {
+    use HasX;
+}
+$c = new C(3);
+echo $c->x, "\n";
+PHP
+            ,
+            "3\n");
+    }
+
+    private function assertMcjitOutput(string $code, string $expected): void
+    {
+        $runtime = new Runtime();
+        $block = $runtime->parseAndCompile($code, 'trait_ctor_promotion.php');
+        $this->assertNotNull($block);
+        $this->assertTrue(Block::containsTraitConstructorOpcodes($block));
+        $this->assertFalse(Block::containsUserClassDeclaredInstancePropertyOpcodes($block));
+        $this->assertFalse(Block::requiresVmLowering($block));
+        $runtime->jit($block, $code, 'trait_ctor_promotion.php');
+        ob_start();
+        $runtime->run($block);
+        $this->assertSame($expected, ob_get_clean());
+    }
+
+    private function declareTraitMcjitLinkSegfaults(): bool
+    {
+        $probe = $this->repoRoot.'/test/repro/trait_empty_mcjit_probe.php';
+        if (!is_file($probe)) {
+            return true;
+        }
+        $cmd = sprintf(
+            'bash -lc %s',
+            escapeshellarg('source '.escapeshellarg($this->repoRoot.'/script/php-env.sh')
+                .' && '.escapeshellarg(PHP_BINARY).' '.escapeshellarg($this->repoRoot.'/bin/jit.php')
+                .' -l '.escapeshellarg($probe).' >/dev/null 2>&1')
+        );
+        exec($cmd, $out, $code);
+
+        return 139 === $code;
+    }
+
+    private function jitRuntimeProbeGreen(): bool
+    {
+        $probe = $this->repoRoot.'/script/jit-runtime-probe.php';
+        $cmd = sprintf(
+            'bash -lc %s',
+            escapeshellarg('source '.escapeshellarg($this->repoRoot.'/script/php-env.sh')
+                .' && '.escapeshellarg(PHP_BINARY).' '.escapeshellarg($probe))
+        );
+        exec($cmd, $out, $code);
+
+        return 0 === $code && str_contains(implode("\n", $out), 'jit-runtime-probe OK');
+    }
+}