Bug#787217: clang++-3.7 generates wrong code with -O1 or -O2

[Thibaut Paumard]

Control: tag -1 upstream

Hi,

I just downloaded and built clang from svn. The bug is present there.

Regards, Thibaut.

Le 29/05/2015 22:51, Thibaut Paumard a écrit :
> Package: clang-3.7
> Version: 1:3.7~svn230892-1
> Severity: important
> File: /usr/bin/clang++-3.7
> 
> Hi,
> 
> when I build the following code with
>  clang++-3.7 -O2 -o foo foo.C
> and then run ./foo, I get a SIGFPE. The example is minimal (if you remove the
> cerr before, no SIGFPE). That means that the code is taking the wrong path in
> the "if" clause. If you uncomment any of the two cerr within the "if", not
> SIGFPE anymore.
> 
> This does not affect clang++3.4 or 3.5, it does also affect clang++-3.7 with
> -O1 but not not -O0.
> 
> I haven't checked yet whether that affects upstream as well.
> 
> Kind regards, Thibaut.
> 
> foo.C -----
> 
> #include <iostream>
> #include <fenv.h>
> 
> double computeCst(double QQ) {
>   std::cerr << "foo\n" << std::endl;
>   if (QQ==0) {
>     //std::cerr << "right path\n";
>     return 1.;
>   } else {
>     //std::cerr << "wrong path\n";
>     return 1/QQ;
>   }
> }
> 
> int main(int argc, char *argv[]) {
>   feenableexcept(FE_DIVBYZERO);
>   computeCst(0.);
>   return 0;
> }
> 
> 
> 
> -- System Information:
> Debian Release: 8.0
>   APT prefers stable
>   APT policy: (990, 'stable')
> Architecture: amd64 (x86_64)
> Foreign Architectures: i386
> 
> Kernel: Linux 3.16.0-4-amd64 (SMP w/8 CPU cores)
> Locale: LANG=fr_FR.utf8, LC_CTYPE=fr_FR.utf8 (charmap=UTF-8)
> Shell: /bin/sh linked to /bin/dash
> Init: systemd (via /run/systemd/system)
> 
> Versions of packages clang-3.7 depends on:
> ii  binutils                 2.25-5
> ii  libc6                    2.19-18
> ii  libc6-dev                2.19-18
> ii  libclang-common-3.7-dev  1:3.7~svn230892-1
> ii  libclang1-3.7            1:3.7~svn230892-1
> ii  libedit2                 3.1-20140620-2
> ii  libffi6                  3.1-2+b2
> ii  libgcc-4.9-dev           4.9.2-10
> ii  libgcc1                  1:4.9.2-10
> ii  libllvm3.7               1:3.7~svn230892-1
> ii  libobjc-4.9-dev          4.9.2-10
> ii  libstdc++-4.9-dev        4.9.2-10
> ii  libstdc++6               4.9.2-10
> ii  libtinfo5                5.9+20140913-1+b1
> ii  zlib1g                   1:1.2.8.dfsg-2+b1
> 
> Versions of packages clang-3.7 recommends:
> pn  llvm-3.7-dev  <none>
> ii  python        2.7.9-1
> 
> Versions of packages clang-3.7 suggests:
> pn  clang-3.7-doc  <none>
> pn  gnustep        <none>
> pn  gnustep-devel  <none>
> 
> -- no debconf information
>