optimize: convert for-loop post-inc/dec to prefix to avoid zval copy (#79)

* optimize: convert for-loop post-inc/dec to prefix to avoid zval copy

For-loop post-expressions (third clause of `for (init; cond; post)`) always
discard the return value, so $i++ is semantically identical to ++$i in this
context. Converting to prefix increment/decrement avoids the zval copy +
destructor overhead from operator++(int)'s return value, saving ~6ns per
increment per loop iteration.

Changes:
- LoopControlTrait: convert PostInc→PreInc, PostDec→PreDec in for-loop
  post-expressions only (while/do-while body untouched)
- Add phpunit test verifying generated C++ contains ++i/--i for for-loops
  and retains i++ in while/do-while bodies
- Add test data file with 7 test functions covering basic, multi-post,
  nested, mixed, and while/do-while cases

* fix: restrict for-loop post-expr rewrite to simple variables only

phpunit/code/loop/for-loop-post-expr-opt.php

@@ -0,0 +1,97 @@
+<?php
+
+function test_post_inc_basic(): void {
+    $sum = 0;
+    for ($i = 0; $i < 10; $i++) {
+        $sum += $i;
+    }
+}
+
+function test_post_dec_basic(): void {
+    $sum = 0;
+    for ($i = 10; $i > 0; $i--) {
+        $sum += $i;
+    }
+}
+
+function test_multi_post(): void {
+    for ($i = 0, $j = 10; $i < 5; $i++, $j--) {
+    }
+}
+
+function test_mixed_post(): void {
+    $j = 0;
+    for ($i = 0; $i < 10; $i++, $j += 2) {
+    }
+}
+
+function test_nested_for(): void {
+    for ($i = 0; $i < 5; $i++) {
+        for ($j = 0; $j < 5; $j++) {
+        }
+    }
+}
+
+function test_while_not_affected(): void {
+    $i = 0;
+    while ($i < 10) {
+        $i++;
+    }
+}
+
+function test_do_while_not_affected(): void {
+    $i = 0;
+    do {
+        $i++;
+    } while ($i < 10);
+}
+
+// --- Cases that must NOT be rewritten (property/static-property/array-element) ---
+
+class Counter {
+    public int $value = 0;
+}
+
+class StaticCounter {
+    public static int $count = 0;
+}
+
+function test_property_post_inc_not_rewritten(): void {
+    $obj = new Counter();
+    for ($i = 0; $i < 10; $i++) {
+        $obj->value++;
+    }
+}
+
+function test_property_post_dec_not_rewritten(): void {
+    $obj = new Counter();
+    for ($i = 0; $i < 10; $i++) {
+        $obj->value--;
+    }
+}
+
+function test_static_property_post_inc_not_rewritten(): void {
+    for ($i = 0; $i < 10; $i++) {
+        StaticCounter::$count++;
+    }
+}
+
+function test_static_property_post_dec_not_rewritten(): void {
+    for ($i = 0; $i < 10; $i++) {
+        StaticCounter::$count--;
+    }
+}
+
+function test_array_element_post_inc_not_rewritten(): void {
+    $arr = [0, 0, 0];
+    for ($i = 0; $i < 10; $i++) {
+        $arr[$i % 3]++;
+    }
+}
+
+function test_array_element_post_dec_not_rewritten(): void {
+    $arr = [10, 10, 10];
+    for ($i = 0; $i < 10; $i++) {
+        $arr[$i % 3]--;
+    }
+}

phpunit/src/LoopControlTest.php

@@ -30,4 +30,35 @@ class LoopControlTest extends \BaseTest
             'control-flow/while-body-defined-condition.php',
         );
     }
+
+    public function testForLoopPostIncConvertedToPreInc(): void
+    {
+        global $translator;
+        $compiler = \TypePhp\CompilerTest::create(TYPEPHP_ROOT_PATH);
+        $translator = $compiler;
+        $testFile = __DIR__ . '/../code/loop/for-loop-post-expr-opt.php';
+        $compiler->addFiles([$testFile]);
+        $compiler->prepareFile($testFile);
+        $cppFile = $compiler->convertFile($testFile);
+        $cpp = file_get_contents($cppFile);
+
+        // for-loop post-expression $i++ → ++$i, $i-- → --$i
+        $this->assertStringContainsString('++i', $cpp);
+        $this->assertStringContainsString('--i', $cpp);
+
+        // while/do-while body $i++ should NOT be converted — still i++
+        $this->assertStringContainsString("\ti++;\n", $cpp);
+
+        // property postfix must NOT be rewritten — still postfix
+        $this->assertMatchesRegularExpression('/\.attr\([^)]+\)[^;]*\+\+/', $cpp);
+        $this->assertMatchesRegularExpression('/\.attr\([^)]+\)[^;]*--/', $cpp);
+
+        // static-property postfix must NOT be rewritten
+        $this->assertMatchesRegularExpression('/getStaticProperty\([^)]+\)[^;]*\+\+/', $cpp);
+        $this->assertMatchesRegularExpression('/getStaticProperty\([^)]+\)[^;]*--/', $cpp);
+
+        // array-element postfix must NOT be rewritten
+        $this->assertMatchesRegularExpression('/\.item\([^)]+\)[^;]*\+\+/', $cpp);
+        $this->assertMatchesRegularExpression('/\.item\([^)]+\)[^;]*--/', $cpp);
+    }
 }

src/Parser/LoopControlTrait.php

@@ -85,6 +85,14 @@ trait LoopControlTrait
 
         $list_loop = [];
         foreach ($loop as $expr) {
+            // for-loop post-expressions discard return value, so $i++ ≡ ++$i.
+            // Only rewrite simple variables; TypePHP lowers prefix and postfix
+            // differently for compound lvalues (e.g. static-property write-back).
+            if ($expr instanceof Node\Expr\PostInc && $this->isVarExpr($expr->var)) {
+                $expr = new Node\Expr\PreInc($expr->var, $expr->getAttributes());
+            } elseif ($expr instanceof Node\Expr\PostDec && $this->isVarExpr($expr->var)) {
+                $expr = new Node\Expr\PreDec($expr->var, $expr->getAttributes());
+            }
             [$loopExpr, $beforeStmts, $afterStmts] = $this->parseExprWithCapturedStmts($expr);
             $loopExpr = $this->stringifyParsedExpr($loopExpr);
             if ($beforeStmts || $afterStmts) {