Re: [PATCH] Fixup possible VR_ANTI_RANGE value_range issues

[Aldy Hernandez <aldyh@redhat.com>]

On 2/27/23 14:58, Richard Biener wrote:
> After fixing PR107561 the following avoids looking at VR_ANTI_RANGE
> ranges where it doesn't seem obvious the code does the correct
> thing here (lower_bound and upper_bound do not work as expected).

I do realize there's some confusion here, and some of it is my fault. 
This has become obvious in my upcoming work removing all of legacy.

What's going on is that ultimately min/max are broken with (non-legacy) 
iranges.  Or at the very least inconsistent between legacy and 
non-legacy.  These are left over from the legacy world, and have been 
marked DEPRECATED for a few releases, but the middle end warnings 
continued to use them and even added new uses after they were obsoleted.

min/max have different meanings depending on kind(), which is also 
deprecated, btw.  They are the underlying min/max fields from the legacy 
implementation, and thus somewhat leak the implementation details. 
Unfortunately, they are being called from non-legacy code which is 
ignoring the kind() field.

In retrospect I should've converted everything away from min/max/kind 
years ago, or at the very least converted min/max to work with 
non-legacy more consistently.

For the record:

   enum value_range_kind kind () const;		// DEPRECATED
   tree min () const;				// DEPRECATED
   tree max () const;				// DEPRECATED
   bool symbolic_p () const;			// DEPRECATED
   bool constant_p () const;			// DEPRECATED
   void normalize_symbolics ();			// DEPRECATED
   void normalize_addresses ();			// DEPRECATED
   bool may_contain_p (tree) const;		// DEPRECATED
   bool legacy_verbose_union_ (const class irange *);	// DEPRECATED
   bool legacy_verbose_intersect (const irange *);	// DEPRECATED

In my local branch I tried converting all the middle-end legacy API uses 
to the new API, but a bunch of tests started failing, and lots more 
false positives started showing up in correct code.  I suspect that's 
part of the reason legacy continued to be used in these passes :-/.  As 
you point out in the PR, the tests seem designed to test the current (at 
times broken) implementation.

That being said, the 5 fixes in your patch are not wrong to begin with, 
because all uses guard lower_bound() and upper_bound() which work 
correctly.  They return the lowest and uppermost possible bound for the 
range (ignoring the underlying implementation).  So, the lower bound of 
a signed non-zero is -INF because ~[0,0] is really [-INF,-1][1,+INF]. 
In the min/max legacy code, min() of signed non-zero (~[0,0]) is 0.  The 
new implementation has no concept of anti-ranges, and we don't leak any 
of that out.

Any uses of min/max without looking at kind() are definitely broken. 
OTOH uses of lower/upper_bound are fine and should work with both legacy 
and non-legacy.

Unrelated, but one place where I haven't been able to convince myself 
that the use is correct is bounds_of_var_in_loop:

> /* Check if init + nit * step overflows.  Though we checked
> 		     scev {init, step}_loop doesn't wrap, it is not enough
> 		     because the loop may exit immediately.  Overflow could
> 		     happen in the plus expression in this case.  */
> 		  if ((dir == EV_DIR_DECREASES
> 		       && compare_values (maxvr.min (), initvr.min ()) != -1)
> 		      || (dir == EV_DIR_GROWS
> 			  && compare_values (maxvr.max (), initvr.max ()) != 1))

Ughh...this is all slated to go away, and I have patches removing all of 
legacy and the old API.

Does this help?  Do you still think lower and upper bound are not 
working as expected?

Aldy

> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> OK?
> 
> Thanks,
> Richard.
> 
> 	* gimple-ssa-sprintf.cc (get_int_range): Avoid VR_ANTI_RANGE
> 	by using range_int_cst_p.
> 	(format_integer): Likewise.
> 	(handle_printf_call): Guard against VR_ANTI_RANGE.
> 	* graphite-sese-to-poly.cc (add_param_constraints): Likewise.
> 	* tree-ssa-strlen.cc (set_strlen_range): Likewise.
> ---
>   gcc/gimple-ssa-sprintf.cc    | 6 +++---
>   gcc/graphite-sese-to-poly.cc | 2 +-
>   gcc/tree-ssa-strlen.cc       | 2 +-
>   3 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/gimple-ssa-sprintf.cc b/gcc/gimple-ssa-sprintf.cc
> index 18975708d2c..61974072f62 100644
> --- a/gcc/gimple-ssa-sprintf.cc
> +++ b/gcc/gimple-ssa-sprintf.cc
> @@ -1082,7 +1082,7 @@ get_int_range (tree arg, gimple *stmt,
>   	  value_range vr;
>   	  query->range_of_expr (vr, arg, stmt);
>   
> -	  if (!vr.undefined_p () && !vr.varying_p ())
> +	  if (range_int_cst_p (&vr))
>   	    {
>   	      HOST_WIDE_INT type_min
>   		= (TYPE_UNSIGNED (argtype)
> @@ -1391,7 +1391,7 @@ format_integer (const directive &dir, tree arg, pointer_query &ptr_qry)
>         value_range vr;
>         ptr_qry.rvals->range_of_expr (vr, arg, dir.info->callstmt);
>   
> -      if (!vr.varying_p () && !vr.undefined_p ())
> +      if (range_int_cst_p (&vr))
>   	{
>   	  argmin = wide_int_to_tree (TREE_TYPE (arg), vr.lower_bound ());
>   	  argmax = wide_int_to_tree (TREE_TYPE (arg), vr.upper_bound ());
> @@ -4623,7 +4623,7 @@ handle_printf_call (gimple_stmt_iterator *gsi, pointer_query &ptr_qry)
>   	  value_range vr;
>   	  ptr_qry.rvals->range_of_expr (vr, size, info.callstmt);
>   
> -	  if (!vr.undefined_p ())
> +	  if (!vr.undefined_p () && vr.kind () != VR_ANTI_RANGE)
>   	    {
>   	      tree type = TREE_TYPE (size);
>   	      tree tmin = wide_int_to_tree (type, vr.lower_bound ());
> diff --git a/gcc/graphite-sese-to-poly.cc b/gcc/graphite-sese-to-poly.cc
> index fbe7667380a..b89262640ac 100644
> --- a/gcc/graphite-sese-to-poly.cc
> +++ b/gcc/graphite-sese-to-poly.cc
> @@ -426,7 +426,7 @@ add_param_constraints (scop_p scop, graphite_dim_t p, tree parameter)
>   
>     if (INTEGRAL_TYPE_P (type)
>         && get_range_query (cfun)->range_of_expr (r, parameter)
> -      && !r.undefined_p ())
> +      && range_int_cst_p (&r))
>       {
>         min = r.lower_bound ();
>         max = r.upper_bound ();
> diff --git a/gcc/tree-ssa-strlen.cc b/gcc/tree-ssa-strlen.cc
> index 7508c1768a5..e1230522564 100644
> --- a/gcc/tree-ssa-strlen.cc
> +++ b/gcc/tree-ssa-strlen.cc
> @@ -1936,7 +1936,7 @@ set_strlen_range (tree lhs, wide_int min, wide_int max,
>   	{
>   	  value_range r;
>   	  get_range_query (cfun)->range_of_expr (r, bound);
> -	  if (!r.undefined_p ())
> +	  if (range_int_cst_p (&r))
>   	    {
>   	      /* For a bound in a known range, adjust the range determined
>   		 above as necessary.  For a bound in some anti-range or