[llvm-bugs] [Bug 26629] New: wrong code (SIGFPE) for packed struct at -Os and above on x86_64-linux-gnu (in 32-bit mode)

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26629

            Bug ID: 26629
           Summary: wrong code (SIGFPE) for packed struct at -Os and above
                    on x86_64-linux-gnu (in 32-bit mode)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -Os and above in 32-bit mode (but not in 64-bit mode).  

This is a regression from 3.7.x. 


$ clang-trunk -v
clang version 3.9.0 (trunk 260876)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/tools/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$
$ clang-trunk -m32 -O1 small.c; ./a.out
$ clang-3.7 -m32 -Os small.c; ./a.out
$ clang-trunk -m64 -Os small.c; ./a.out
$
$ clang-trunk -m32 -Os small.c
$ ./a.out
Floating point exception (core dumped)
$


---------------------------------------------


#pragma pack(1)
struct S
{ 
  unsigned f0:13;
  int f1:19;
  int f2:27;
  int f3:8;
} a;

int b, c;

int
main ()
{ 
  struct S d = { 4, 5, 10878, 1 };
  for (; b < 7; b++)
    { 
      int e = d.f1 | (d.f0 && 5 % d.f3);
      int f = c - d.f0;
      d.f2 = e;
      d.f0 = f;
    }
  a = d;
  return 0;
}

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