[LLVMbugs] [Bug 20494] New: wrong code at -O2 and -O3 on x86_64-linux-gnu (only in 64-bit mode and affecting all clang versions)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20494

            Bug ID: 20494
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu (only in
                    64-bit mode and affecting all clang versions)
           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 current clang trunk miscompiles the following code at -O2 and -O3 on
x86_64-linux-gnu in 64-bit mode (but not in 32-bit mode). 

This also affects earlier clang versions (including at least 3.0 and later). 

$ clang-trunk -v
clang version 3.6.0 (trunk 214258)
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 multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-trunk -m64 -Os small.c; a.out
2
$ clang-trunk -m32 -O2 small.c; a.out
2
$ 
$ clang-trunk -m64 -O2 small.c; a.out
-2147483647
$ clang-3.4 -m64 -O2 small.c; a.out
-2147483647
$ clang-3.3 -m64 -O2 small.c; a.out
-2147483647
$ 


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


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

int a, h;
volatile int c;
short b, g[2]; 
char d, e;
long f;

int
fn1 (unsigned int p)
{
  int i;
  for (i = 0; i < 1; i++)
    for (e = 1; e; e++)
      {
    d = p % 3;
    c;
      }
  return p;
}

int
main ()
{
  for (h = 0; h < 2; h++)
    g[h] = -8;
  f = a && 1;
  b = fn1 (g[0] ^ f);
  printf ("%d\n", d);
  return 0;
}

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