[LLVMbugs] [Bug 19132] New: wrong code (that hangs) by LTO on x86_64-linux-gnu (affecting 3.4 and trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19132

            Bug ID: 19132
           Summary: wrong code (that hangs) by LTO on x86_64-linux-gnu
                    (affecting 3.4 and trunk)
           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 and 3.4 miscompile the following code when using LTO on
x86_64-linux-gnu in both 32-bit and 64-bit modes. 

This is a regression from clang 3.3. 

This should be different from http://llvm.org/bugs/show_bug.cgi?id=19111 as
19111 also fails for 3.2 and 3.3. 

$ clang-trunk -v
clang version 3.5.0 (trunk 203791)
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 foo.c main.c
$ a.out
$ 
$ clang-3.3 -flto -O0 -c foo.c
$ clang-3.3 -flto -O1 -c main.c
$ clang-3.3 -flto -O1 foo.o main.o
$ a.out
$ 
$ clang-trunk -flto -O0 -c foo.c
$ clang-trunk -flto -O1 -c main.c
$ clang-trunk -flto -O1 foo.o main.o
$ a.out
^C
$ 
$ clang-3.4 -flto -O0 -c foo.c
$ clang-3.4 -flto -O1 -c main.c
$ clang-3.4 -flto -O1 foo.o main.o
$ a.out
^C
$ 
$ 
$ cat foo.c
extern int a, c;

static int
bar (int p1, int p2)
{
  return p2 + 1;
}

void
foo (void)
{
  int e = 0, g = 0, b = 1;
  a = (b == 0 ? 0 : b);
  if (bar (a || 0, g) & 1)
    a = e && 0;
}
$ cat main.c
extern int foo (void);

int a, c;

int
main ()
{
  for (; c < 2; c++)
    foo ();
  return 0;
}

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