[LLVMbugs] [Bug 17780] New: wrong code at -O2 and -Os on x86_64-linux-gnu in 32-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17780

            Bug ID: 17780
           Summary: wrong code at -O2 and -Os on x86_64-linux-gnu in
                    32-bit mode
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O2 and -Os in both 32-bit mode. 

This is a regression from clang 3.3. 

$ clang-trunk -v
clang version 3.4 (trunk 193897)
Target: x86_64-pc-linux-gnu
Thread model: posix
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/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -m32 -O1 small.c; a.out
0
$ clang-trunk -m32 -O2 small.c; a.out
1
$ clang-trunk -m32 -Os small.c; a.out
1
$ clang-3.3 -m32 -O2 small.c; a.out
0
$ clang-3.3 -m32 -Os small.c; a.out
0
$ gcc-4.8.2 -m32 -O2 small.c; a.out
0
$ icc -m32 -O2 small.c; a.out
0
$ 


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


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

union U
{
  int f1;
  int f2;
} a = {1};

static int
foo (union U p)
{
  for (a.f2 = 0; a.f2 < 1; a.f2++)
    if (p.f2)
      break;
  return 0;
}

int
main ()
{
  foo (a);
  printf ("%d\n", a.f1);
  return 0;
}

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