[LLVMbugs] [Bug 19798] New: LTO crashes with linker error on valid code at -O1 (also -Os and -O2) on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19798

            Bug ID: 19798
           Summary: LTO crashes with linker error on valid code at -O1
                    (also -Os and -O2) 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 causes a linker error when it is compiled on
x86_64-linux-gnu by the current clang trunk using LTO at -O1 (also -Os and -O2)
in both 32-bit and 64-bit modes.  

This is a regression from clang 3.4. 

$ clang-trunk -v
clang version 3.5.0 (trunk 209103)
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 -O1 small.c; a.out
$ clang-trunk -flto -O0 small.c; a.out
$ clang-3.4 -flto -O1 small.c; a.out
$ 
$ clang-trunk -flto -O1 small.c
ld: /tmp/llvm/include/llvm/Support/Casting.h:237: typename llvm::cast_retty<X,
Y*>::ret_type llvm::cast(Y*) [with X = llvm::PHINode; Y = llvm::Instruction;
typename llvm::cast_retty<X, Y*>::ret_type = llvm::PHINode*]: Assertion
`isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
clang: error: unable to execute command: Aborted (core dumped)
clang: error: linker command failed due to signal (use -v to see invocation)
$ 


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


int a, c, d[2] = { 0, 1 }, e;

volatile int b;

int
main ()
{
  for (; a < 1; a++)
    for (; c < 1; c++)
      {
    if (d[1])
      continue;
    for (; e < 1; e++)
      a && b;
      }
  return 0;
}

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