From: "shyouhei (Shyouhei Urabe)" <shyouhei@...>
Date: 2012-07-15T20:04:06+09:00
Subject: [ruby-core:46488] [ruby-trunk - Bug #6736] Avoid misoptimization due to division by zero


Issue #6736 has been updated by shyouhei (Shyouhei Urabe).


The patch seems OK to me.
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Bug #6736: Avoid misoptimization due to division by zero
https://bugs.ruby-lang.org/issues/6736#change-28126

Author: xi (Xi Wang)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0
ruby -v: trunk


In time.c (quo) we have:

        if (b == 0) rb_num_zerodiv();
        c = a / b;

This code pattern is dangerous.  Some C compilers may move the division _before_ the check because:

1) It appears to the compiler that the division a / b is always reachable even with b == 0 (though rb_num_zerodiv invokes rb_raise internally).

2) Division by zero is undefined behavior.

This happened to PostgreSQL before.

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=616180

Attached patch marks rb_num_zerodiv as NORETURN to avoid this issue.


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