Description:
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The attached code behaves differently when Zend-compiled versus not. (It breaks when Zend-compiled). It looks like maybe the for-loop is getting optimized away, incorrectly. The Zend Optimizer running on the server is: Zend Optimizer v2.5.5. I'll post the version of the Zend compiler when I get a chance to look it up. I lied about the PHP version (4.3.9) because upgrading to test is not practical, but it seems to depend on the encoder version, not the PHP version.

Reproduce code:
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function include_next() {
        # Infer the calling file from the backtrace
        $bt = debug_backtrace();
        for ($i=0; $bt[$i] && !$bt[$i]['file']; $i++);
        $caller = $bt[$i]['file'];
        assert($caller);
        // ... do some stuff with $caller
}

Expected result:
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I expect the assertion to NOT fail.

Actual result:
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Assertion fails.