[LLVMbugs] [Bug 20063] New: wrong code at -O2 and -O3 on x86_64-linux-gnu in 64-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20063

            Bug ID: 20063
           Summary: wrong code at -O2 and -O3 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 at -O2 and -O3 on
x86_64-linux-gnu in 64-bit mode (but not in 32-bit mode). 

This is a regression from 3.4. 


$ clang-trunk -v
clang version 3.5.0 (trunk 211006)
Target: x86_64-unknown-linux-gnu
Thread model: posix
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 -Os small.c; a.out
0
$ clang-trunk -m32 -O2 small.c; a.out
0
$ clang-3.4 -m64 -O2 small.c; a.out
0
$ 
$ clang-trunk -m64 -O2 small.c; a.out
1
$ 


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


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

int *a, **b = &a, c = 1, **f = &a, *g = &c; 
char d = 0;
static char *e = &d;

int
main ()
{
  *b = g;

lbl:
  *b = *f;
  (*e)--;
  **b = 0;
  if (d)
    goto lbl;

  printf ("%d\n", c);
  return 0;
}

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