[llvm-bugs] [Bug 28402] New: wrong code (generated code hangs) at -O3 on x86_64-linux-gnu in 32-bit and 64-bit modes

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28402

            Bug ID: 28402
           Summary: wrong code (generated code hangs) at -O3 on
                    x86_64-linux-gnu in 32-bit and 64-bit modes
           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: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O3 in both the 32-bit and 64-bit modes.  

This is a regression from 3.8.x. 


$ clang-trunk -v
clang version 3.9.0 (trunk 274430)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/tools/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
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/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.1.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang-trunk -O2 small.c; ./a.out
$ clang-3.8 -O3 small.c; ./a.out
$ 
$ clang-trunk -O3 small.c
$ timeout -s 9 10 ./a.out
Killed
$ 


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


int a, b, c;
short e = 4, g[3], h;
char f;

struct
{
  int:5;
  int f1:7;
} d;

short
fn1 (int p1, int p2)
{
  return p1 ? p1 : p1 << p2;
}

int
main ()
{
  int i = a - b;
  for (; c; c = i)
    ;
  f = 2;
  for (; f; f--)
    if (e || d.f1 > 1)
      h = fn1 (g[f], 5);
  return 0; 
}

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