Re: [ubsan PATCH] Fix compile-time hog with &TARGET_EXPRs (PR sanitizer/70342)

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Apr 27, 2016 at 07:03:25PM +0200, Marek Polacek wrote:
> This test took forever to compile with -fsanitize=null, because the
> instrumentation was creating incredible amount of duplicated expressions, in a
> quadratic fashion.  I think the problem is that we instrument &TARGET_EXPR <>
> expressions, which doesn't seem to be needed -- we only need to instrument the
> initializers in TARGET_EXPRs.  With this patch, we avoid creating tons of useless
> expressions and the compile time is reduced from ~ infinity to <1s.
> 
> Jakub, do you see any problem with this?
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2016-04-27  Marek Polacek  <polacek@redhat.com>
> 
> 	PR sanitizer/70342
> 	* c-ubsan.c (ubsan_maybe_instrument_reference_or_call): Don't
> 	null-instrument &TARGET_EXPR <...>.
> 
> 	* g++.dg/ubsan/null-7.C: New test.

I wonder if this wouldn't be better handled in tree_single_nonzero_warnv_p,
perhaps like:

     case ADDR_EXPR:
       {
 	tree base = TREE_OPERAND (t, 0);
 
 	if (!DECL_P (base))
 	  base = get_base_address (base);
+
+	if (base && TREE_CODE (base) == TARGET_EXPR)
+	  base = TARGET_EXPR_SLOT (base);
 	
 	if (!base)
 	  return false;

(untested)?

	Jakub