[LLVMbugs] [Bug 5579] New: Incorrect bitfields arithmetic result with llvm-gcc frontend

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=5579

           Summary: Incorrect bitfields arithmetic result with llvm-gcc
                    frontend
           Product: new-bugs
           Version: 2.5
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: chenyang at cs.utah.edu
                CC: llvmbugs at cs.uiuc.edu, regehr at cs.utah.edu,
                    jxyang at cs.utah.edu


Seems it's a bug of llvm-gcc frontend. See below:

yang at yang-working:~$ llvm-gcc -O1 -o small_llvm small.c
yang at yang-working:~$ ./small_llvm
g = 0
yang at yang-working:~$ clang -O1 -o small_clang small.c
yang at yang-working:~$ ./small_clang
g = 1
yang at yang-working:~$ cat small.c
#include <stdio.h>

struct S0 {
  unsigned f0 : 27;
};

int g = 0;
void foo(void);

void foo()
{
  struct S0 s = {20000000};
  g = (s.f0) < 0xC0000001L;
}

int main(void)
{
  foo();
  printf("g = %d\n", g);
  return 0;
}
yang at yang-working:~$ llvm-gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../llvm-gcc4.2-2.5.source/configure 
--prefix=/mounts/zion/disks/0/localhome/tbrethou/2.5/prerelease2/llvm-gcc/obj/../install 
--program-prefix=llvm- 
--enable-llvm=/localhome/tbrethou/2.5/prerelease2/llvm-2.5/ 
--disable-bootstrap --enable-languages=c,c++,fortran
Thread model: posix
gcc version 4.2.1 (Based on Apple Inc. build 5636) (LLVM build 2.5)
yang at yang-working:~$ clang -v
clang version 1.1 (trunk 85610)
Target: i386-pc-linux-gnu
Thread model: posix


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