[LLVMbugs] [Bug 18862] New: wrong code at -O1 and above on x86_64-linux-gnu in 32-bit mode (for code with the "pack" pragma and bitfields)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18862

            Bug ID: 18862
           Summary: wrong code at -O1 and above on x86_64-linux-gnu in
                    32-bit mode (for code with the "pack" pragma and
                    bitfields)
           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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code is miscompiled by the current clang trunk at -O1 and above
in 32-bit mode (but not 64-bit) on x86_64-linux-gnu. 

This is a regression from 3.4. 

$ clang-trunk -v
clang version 3.5 (trunk 201494)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
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/4.8.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multiilb: .;@m64
Candidate multiilb: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-trunk -m32 -O0 small.c; a.out
0
-2
$ clang-trunk -m64 -O1 small.c; a.out
0
-2
$ clang-3.4 -m32 -O1 small.c; a.out
0
-2
$ 
$ clang-trunk -m32 -O1 small.c; a.out
0
-1
$ 


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


int printf (const char *, ...);

#pragma pack(1)
struct
{
  int f0:9;
  int f1:30;
  int f2:5;
  int f3:23;
  int f4:11;
  int f5:29;
  int f6:24;
  int:14;
} a, b = {0, 0, 0, 0, 0, 0, -2};

int c;

int
main ()
{
  printf ("%d\n", a.f6);
  for (; c < 1; c++)
    printf ("%d\n", b.f6);
  return 0;
}

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