[LLVMbugs] [Bug 17732] New: wrong code at -Os and above on x86_64-linux-gnu (both 32-bit and 64-bit modes)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17732

            Bug ID: 17732
           Summary: wrong code at -Os and above on x86_64-linux-gnu (both
                    32-bit and 64-bit modes)
           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 and clang 3.3 on
x86_64-linux-gnu at -Os and above in both 32-bit and 64-bit modes. 

This is a regression from clang 3.2. 

$ clang-trunk -v
clang version 3.4 (trunk 193653)
Target: x86_64-pc-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/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -O1 small.c; a.out
1
$ clang-trunk -Os small.c; a.out
0
$ clang-3.3 -Os small.c; a.out
0
$ clang-3.2 -Os small.c; a.out
1
$ 


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


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

struct S0
{
  long f2;
  int f3;
  int f4;
  int f5;
};

struct S1
{
  char f0;
} a;

struct S2
{
  int f2;
  int f3;
  struct S0 f4;
  struct S1 f5;
} b;

int i; 

int
main ()
{
  struct S2 c = { 1, 1, {1, 1, 1, 1}, {1} };
  b = c;
  i = c.f4.f5;
  a = b.f5;
  printf ("%d\n", a.f0);
  return 0;
}

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