[LLVMbugs] [Bug 21773] New: wrong code at -Os and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21773

            Bug ID: 21773
           Summary: wrong code at -Os and above 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 current clang trunk miscompiles the following code at -Os and above on
x86_64-linux-gnu in both 32-bit and 64-bit modes.

This is a regression from 3.5.0.  

$ clang-trunk -v
clang version 3.6.0 (trunk 223504)
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
128
$ clang-3.5.0 -Os small.c; a.out
128
$ 
$ clang-trunk -Os small.c; a.out
256
$ 


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


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

int a, c;
short d;

char
fn1 (int p1, int p2)
{
  return p1 * p2;
}

int
main ()
{
 lbl:
  ++a;
  d--;
  c = fn1 (d, 146);
  if (c)
    goto lbl;
  printf ("%d\n", a);
  return 0;
}

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