Description:
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Program received signal SIGSEGV, Segmentation fault.
0x00007ffff548910a in strlen () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff548910a in strlen () from /lib64/libc.so.6
#1  0x0000000000458ffb in zif_date_interval_format ()
#2  0x0000000000749066 in ?? ()
#3  0x00000000006b558b in execute_ex ()
#4  0x0000000000679ade in zend_eval_stringl ()
#5  0x0000000000679c34 in zend_eval_stringl_ex ()
#6  0x000000000074ae6c in ?? ()
#7  0x00000000004563b9 in main ()

Test script:
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<?php
$di = new DateInterval('P1D');
print $d->format("%");