[PATCH] Fix ubsan tree sharing (PR sanitizer/66908)

[Marek Polacek]

On Wed, Jul 22, 2015 at 07:26:22PM +0200, Marek Polacek wrote:
> In this testcase we were generating an uninitialized variable when doing
> -fsanitize=shift,bounds sanitization.  The shift instrumentation is done
> first; after that, the IR looks like
> 
>   res[i] = (m > 31) ? __ubsan (... tab[i] ...) ? 0, ... tab[i] ...;
> 
> where tab[i] are identical.  That means that when we instrument the first
> tab[i] (we shouldn't do this I suppose), the second tab[i] is changed as
> well as they're shared.  But that doesn't play well with SAVE_EXPRs, because
> SAVE_EXPR <i> would only be initialized on one path.  Fixed by unsharing
> the operands when constructing the ubsan check.  The .gimple diff is in
> essence just
> 
> +  i.2 = i;
> +  UBSAN_BOUNDS (0B, i.2, 21);
> -  UBSAN_BOUNDS (0B, i.1, 21);
> 
> (Merely not instrumenting __ubsan_* wouldn't help exactly because of the
> sharing.)
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2015-07-22  Marek Polacek  <polacek@redhat.com>
> 
> 	PR sanitizer/66908
> 	* c-ubsan.c: Include gimplify.h.
> 	(ubsan_instrument_division): Unshare OP0 and OP1.
> 	(ubsan_instrument_shift): Likewise.
> 
> 	* c-c++-common/ubsan/pr66908.c: New test.

I'm backporting this patch to the gcc5 branch as well.

	Marek