Bug #81627 [Nab->Opn]: Incorrect result of php bitwise and with floats using clang13 -O2

Edit report at https://bugs.php.net/bug.php?id=81627&edit=1 ID: 81627 Updated by: requinix@php.net Reported by: shaohua dot li at inf dot ethz dot ch -Summary: Incorrect result of php +Summary: Incorrect result of php bitwise and with floats using clang13 -O2 -Status: Not a bug +Status: Open Type: Bug Package: *General Issues Operating System: Ubuntu 20.04.3 LTS PHP Version: 8.1Git-2021-11-16 (Git) Block user comment: N Private report: N New Comment: I assume you do *not* get the float-to-int deprecation warning when $n=58? PHP doesn't support bitwise AND with floats and will round them to ints, but that comes with branch prediction so -O2 may be running afoul of that. And that there is the limit of my knowledge on this matter. Previous Comments: ------------------------------------------------------------------------ [2021-11-17 08:53:03] shaohua dot li at inf dot ethz dot ch Hi, Even if I decouple the two operations into two statements, the issue still exists. Also, for the robustness, correctness, and consistency of php, the outputs should be the same. Test script: ---------------- <?php function test() { $n = 0; $a = 0; while($a <= 0) { $a &= $a + $a; $a--; if (++$n > 59) die("bug\n"); } } test(); ?> ------------------------------------------------------------------------ [2021-11-16 23:24:03] requinix@php.net > $a &= $a-- + $a; That statements has two modifications to $a: the -- and the &=. PHP does not guarantee in what order those will happen. https://en.wikipedia.org/wiki/Sequence_point ------------------------------------------------------------------------ [2021-11-16 15:49:06] shaohua dot li at inf dot ethz dot ch Description: ------------ Hi there, I compiled php-src twice with clang13 -O0 and -O2 (default). However, for the following code sample, the two ./sapi/cli/php would evaluate it differently. For "clang13 -O0" compiled one, "bug" would be printed. However, "clang13 -O2" wouldn't. Test script: --------------- <?php function test() { $n = $a = 0; while($a <= 0) { $a &= $a-- + $a; if (++$n > 59) die("bug\n"); } } test(); ?> ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=81627&edit=1