[LLVMbugs] [Bug 17975] New: wrong code for bit shifting integer promotion at -O1 and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17975

            Bug ID: 17975
           Summary: wrong code for bit shifting integer promotion at -O1
                    and above on x86_64-linux-gnu
           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 on
x86_64-linux-gnu at -O1 and above in both 32-bit and 64-bit modes. 

It is a regression from clang 3.3. 


$ clang-trunk -v
clang version 3.4 (trunk 194963)
Target: x86_64-unknown-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
257
$ clang-3.3 -O1 small.c; a.out
257
$ 
$ clang-trunk -O1 small.c; a.out
1
$ 


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


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

unsigned char c = 1;
int s;

int
main ()
{
  printf("%d\n", c >> s | c << (8 - s));
  return 0;
}

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