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List: gcc-patches
Subject: Re: Request to merge Undefined Behavior Sanitizer in (take 2)
From: Jason Merrill <jason () redhat ! com>
Date: 2013-07-31 18:52:39
Message-ID: 51F95CF7.8020605 () redhat ! com
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On 07/31/2013 01:33 PM, Marek Polacek wrote:
> There are still at least two issues though, which is why
> bootstrap with -fsanitize=undefined fails:
>
> http://gcc.gnu.org/ml/gcc-patches/2013-07/msg01480.html
This looks like a serious bug, properly caught by -Wuninitialized.
> When sanitizing,
> in .uninit1 we have
> int x.3;
> int x.2;
>
> <bb 2>:
> x.3_3 = x.2_1(D) >> 1;
> x = x.3_3;
Note that x.2 is not initialized.
> and when no sanitizing
> int x.1;
> int x.0;
>
> <bb 2>:
> x.0_2 = x;
> x.1_3 = x.0_2 >> 1;
> x = x.1_3;
But here x.0 is initialized.
> http://gcc.gnu.org/ml/gcc-patches/2013-07/msg01536.html
Here, the C++ compiler is wrong to fold away the division by zero, but
given that bug the folding ought to also eliminate the call to the
sanitize function. Seems like you should attach the call to the
questionable expression itself.
Jason
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