[Bug c++/16568] New: 3.5: wrong code for conditional in initializer

["gcc-bugzilla at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

In the example below, the C constructor is miscompiled.
I compile like this:

$ g++ -S x.cc

Here is the generated code for the constructor (eliding labels used for EH):

_ZN1CC2EP4ystr:
	pushl	%ebp
	movl	%esp, %ebp
	subl	$24, %esp
	cmpl	$0, 12(%ebp)
	jne	.L2
	movl	8(%ebp), %eax
	movl	%eax, -4(%ebp)
	movl	$0, 4(%esp)
	movl	-4(%ebp), %eax
	movl	%eax, (%esp)
	call	_ZN4ystrC1Ei ; ystr::ystr[in-charge](int)
	jmp	.L1
.L2:
	movl	12(%ebp), %eax
	movl	%eax, 4(%esp)
	movl	-4(%ebp), %eax ; !!! read of uninitialized memory
	movl	%eax, (%esp)
	call	_ZN4ystrC1ERKS_ ; ystr::ystr[in-charge](ystr const&)
.L1:
	leave
	ret

In the case that the jne to .L2 is taken, we reference the value
at -4(%ebp).  However, this location is only initialized in the
other branch of the conditional.  Thus, we end up passing an invalid
pointer as the this argument of the constructor.

This problem is seen already in the -original tree dump:

;; Function C::C(ystr*) (_ZN1CC2EP4ystr)
;; enabled by -tree-original
{
  struct ystr * this.0;

  if (value == 0B)
    {
      this.0 = (struct ystr *)this;
      __comp_ctor (this.0, 0);
    }
  else
    {
      __comp_ctor (this.0, value);
    }
}

Environment:
System: Linux karma 2.6.7 #18 Wed Jul 14 03:27:01 EDT 2004 i686 i686 i386 GNU/Linux
Architecture: i686

	<machine, os, target, libraries (multiple lines)>
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: /home/sss/gcc/gcc/configure --prefix=/usr/local/gcc --enable-threads=posix --enable-long-long --enable-languages=c,c++,f95

How-To-Repeat:

-------------------------------------
struct ystr {
  ystr (int);
  ystr (const ystr&);
};

struct C
{
  C(ystr* value);
  ystr _object;
};

C::C(ystr* value)
  : _object(value == 0 ? 0 : *value)
{ 
}

-------------------------------------
------- Additional Comments From snyder at fnal dot gov  2004-07-15 16:11 -------
Fix:
	<how to correct or work around the problem, if known (multiple lines)>

-- 
           Summary: 3.5: wrong code for conditional in initializer
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: snyder at fnal dot gov
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16568