[LLVMbugs] [Bug 19072] New: wrong code by LTO on x86_64-linux-gnu in 64-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19072

            Bug ID: 19072
           Summary: wrong code by LTO on x86_64-linux-gnu in 64-bit mode
           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 when using LTO on
x86_64-linux-gnu in 64-bit mode (but not 32-bit mode). 

$ clang-trunk -v
clang version 3.5.0 (trunk 203119)
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 -O0 fn1.c fn2.c fn3.c main.c
$ a.out
0
$ clang-trunk -flto -O0 -c fn1.c
$ clang-trunk -flto -O1 -c fn2.c
$ clang-trunk -flto -O0 -c fn3.c
$ clang-trunk -flto -O0 -c main.c 
$ clang-trunk -flto -O1 fn1.o fn2.o fn3.o main.o
$ a.out
1293820360
$ 
$ 
$ cat fn1.c
extern int d;

void
fn1 (int p)
{
  if (!p)
    d = 0;
}
$ cat fn2.c
extern void fn1 (int); 
extern short b;

void
fn2 (void)
{
  for (b = 1; b; b++)
    fn1 (b);
}
$ cat fn3.c
extern void fn2 (void); 
extern volatile int c;
extern int d;

void
fn3 (void)
{
  fn2 ();
  int e = 0, t;
  if (d)
    {
      t = e || e ? 0 : e;
      c;
    }
}
$ cat main.c
extern int printf (const char *, ...);
extern void fn3 (void);

int a[6];
short b; 
volatile int c;
int d = 1; 

int
main ()
{
  a[1] = 0;
  fn3 ();
  printf ("%d\n", a[a[0]]);
  return 0;
}

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