[LLVMbugs] [Bug 21295] New: wrong code at -Os and above on x86_64-linux-gnu in 32-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21295

            Bug ID: 21295
           Summary: wrong code at -Os and above on x86_64-linux-gnu in
                    32-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 following code is miscompiled by the current clang trunk (as well as 3.3
and later) on x86_64-linux-gnu at -Os and above in 32-bit mode (but not in
64-bit mode). 

This is a regression from 3.2.

$ clang-trunk -v
clang version 3.6.0 (trunk 219779)
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 -m32 -O1 small.c; a.out
-1
$ clang-trunk -m64 -Os small.c; a.out
-1
$ clang-3.2 -m32 -Os small.c; a.out
-1
$ 
$ clang-trunk -m32 -Os small.c; a.out
-12
$ clang-3.5.0 -m32 -Os small.c; a.out
-12
$ clang-3.4.2 -m32 -Os small.c; a.out
1
$ clang-3.4.1 -m32 -Os small.c; a.out
1
$ clang-3.4 -m32 -Os small.c; a.out
1
$ clang-3.3 -m32 -Os small.c; a.out
1
$ 


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


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

struct S0
{
  char f2;
  int f3;
  char f4;
  char f5;
  int f7;
  int f8;
};

struct S1
{
  struct S0 f1;
  struct S0 f4;
};

struct S3
{
  struct S1 f4;
  struct S0 f5;
} a, b;

struct S3
fn1 (struct S3 p)
{
  struct S1 c = { {0, 0, 0, 0, 0, 0}, {-1, 0, 0, 0, 0, 0} };
  if (a.f5.f4)
    p.f4 = a.f4;
  else
    p.f4.f1 = c.f4;
  return p;
}

int
main ()
{
  struct S3 d = { {{0, 0, 0, 0, 0, 0}, {0, 0, -1, 1, 0, 0}}, {0, 0, 0, 0, 0, 0}
};
  b = fn1 (d);
  printf ("%d\n", b.f4.f1.f2);
  return 0;
}

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