[LLVMbugs] [Bug 17827] New: wrong code at -O1 and above on x86_64-linux-gnu (affecting clang trunk, 3.3, and 3.2)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17827

            Bug ID: 17827
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
                    (affecting clang trunk, 3.3, and 3.2)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          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 (as well as clang
3.2 and 3.3) on x86_64-linux-gnu at -O1 and above in both 32-bit and 64-bit
modes.  

It is a regression from clang 3.1. 

$ clang-trunk -v
clang version 3.4 (trunk 194075)
Target: x86_64-pc-linux-gnu
Thread model: posix
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/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -O0 small.c; a.out
1
$ clang-3.1 -O1 small.c; a.out
1
$         
$ clang-trunk -O1 small.c; a.out
0
$ clang-3.3 -O1 small.c; a.out
0
$ clang-3.2 -O1 small.c; a.out
0
$ 
$ gcc-trunk -O1 small.c; a.out
1
$ icc -O1 small.c; a.out
1
$ 


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


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

struct S
{
  int f0;
  int:1;
  int f1:8;
  int f2;
} a;

int b;

void
foo (int p)
{
  struct S c = a;
  c.f1 = p & 190;
  b = c.f1 < 1;
}

int
main ()
{
  foo (174);
  printf ("%d\n", b);
  return 0;
}

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