Re: [PATCH 1/5] Common API for accessing global and on-demand ranges.

[Martin Sebor <msebor@gmail.com>]

On 5/21/21 5:39 AM, Aldy Hernandez via Gcc-patches wrote:
> This patch provides a generic API for accessing global ranges.  It is
> meant to replace get_range_info() and get_ptr_nonnull() with one
> common interface.  It uses the same API as the ranger (class
> range_query), so there will now be one API for accessing local and
> global ranges alike.
> 
> Follow-up patches will convert all users of get_range_info and
> get_ptr_nonnull to this API.
> 
> For get_range_info, instead of:
> 
>    if (!POINTER_TYPE_P (TREE_TYPE (name)) && SSA_NAME_RANGE_INFO (name))
>      get_range_info (name, vr);
> 
> You can now do:
> 
>    RANGE_QUERY (cfun)->range_of_expr (vr, name, [stmt]);
> 
> ...as well as any other of the range_query methods (range_on_edge,
> range_of_stmt, value_of_expr, value_on_edge, value_on_stmt, etc).
> 
> As per the API, range_of_expr will work on constants, SSA names, and
> anything we support in irange::supports_type_p().
> 
> For pointers, the interface is the same, so instead of:
> 
>    else if (POINTER_TYPE_P (TREE_TYPE (name)) && SSA_NAME_PTR_INFO (name))
>      {
>        if (get_ptr_nonnull (name))
>          stuff();
>      }
> 
> One can do:
> 
>    RANGE_QUERY (cfun)->range_of_expr (vr, name, [stmt]);
>    if (vr.nonzero_p ())
>      stuff ();
> 
> Along with this interface, we are providing a mechanism by which a
> pass can use an on-demand ranger transparently, without having to
> change its code.  Of course, this assumes all get_range_info() and
> get_ptr_nonnull() users have been converted to the new API, which
> follow-up patches will do.
> 
> If a pass would prefer to use an on-demand ranger with finer grained
> and context aware ranges, all it would have to do is call
> enable_ranger() at the beginning of the pass, and disable_ranger() at
> the end of the pass.
> 
> Note, that to use context aware ranges, any user of range_of_expr()
> would need to pass additional context.  For example, the optional
> gimple statement (or perhaps use range_on_edge or range_of_stmt).
> 
> The observant reader will note that RANGE_QUERY is tied to cfun, which
> may not be available in certain contexts, such as at RTL time,
> gimple-fold, or some other places where we may or may not have cfun
> set.
> 
> For cases where we are sure there is no cfun, you can use
> GLOBAL_RANGE_QUERY instead of RANGE_QUERY(cfun).  The API is the same.
> 
> For cases where a function may be called with or without a function,
> you could use the following idiom:
> 
>    range_query *query = cfun ? RANGE_QUERY (cfun) : GLOBAL_RANGE_QUERY;
> 
>    query->range_of_expr (range, expr, [stmt]);
> 
> By default RANGE_QUERY uses GLOBAL_RANGE_QUERY, unless the user has
> enabled an on-demand ranger with enable_ranger(), in which case it
> will use the currently active ranger.  That is, until disable_ranger()
> is called, at which point, we revert back to GLOBAL_RANGE_QUERY.
> 
> We think this provides a generic way of accessing ranges, both
> globally and locally, without having to keep track of types,
> SSA_NAME_RANGE_INFO, and SSA_NAME_PTR_INFO.  We also hope this can be
> used to transition passes from global to on-demand ranges when
> appropriate.

Thanks for the heads up!  This sounds great (and thanks for all
the work converting the existing uses).  Just a few comments on
the changes.

> 
> Tested on x86-64 Linux.
> 
> OK?
> 
> gcc/ChangeLog:
> 
> 	* function.c (allocate_struct_function): Set cfun->x_range_query.
> 	* function.h (struct function): Declare x_range_query.
> 	(RANGE_QUERY): New.
> 	(get_global_range_query): New.
> 	(GLOBAL_RANGE_QUERY): New.
> 	* gimple-range-cache.cc (ssa_global_cache::ssa_global_cache):
> 	Remove call to safe_grow_cleared.
> 	* gimple-range.cc (get_range_global): New.
> 	(gimple_range_global): Move from gimple-range.h.
> 	(get_global_range_query): New.
> 	(global_range_query::range_of_expr): New.
> 	(enable_ranger): New.
> 	(disable_ranger): New.
> 	* gimple-range.h (gimple_range_global): Move to gimple-range.cc.
> 	(class global_range_query): New.
> 	(enable_ranger): New.
> 	(disable_ranger): New.
> 	* gimple-ssa-evrp.c (evrp_folder::~evrp_folder): Rename
> 	dump_all_value_ranges to dump.
> 	* tree-vrp.c (vrp_prop::finalize): Same.
> 	* value-query.cc (range_query::dump): New.
> 	* value-query.h (range_query::dump): New.
> 	* vr-values.c (vr_values::dump_all_value_ranges): Rename to...
> 	(vr_values::dump): ...this.
> 	* vr-values.h (class vr_values): Rename dump_all_value_ranges to
> 	dump and make virtual.
> ---
>   gcc/function.c            |   4 ++
>   gcc/function.h            |  16 +++++
>   gcc/gimple-range-cache.cc |   1 -
>   gcc/gimple-range.cc       | 130 ++++++++++++++++++++++++++++++++++++++
>   gcc/gimple-range.h        |  60 +++++-------------
>   gcc/gimple-ssa-evrp.c     |   2 +-
>   gcc/tree-vrp.c            |   2 +-
>   gcc/value-query.cc        |   5 ++
>   gcc/value-query.h         |   1 +
>   gcc/vr-values.c           |   2 +-
>   gcc/vr-values.h           |   2 +-
>   11 files changed, 175 insertions(+), 50 deletions(-)
> 
> diff --git a/gcc/function.c b/gcc/function.c
> index fc7b147b5f1..67576950983 100644
> --- a/gcc/function.c
> +++ b/gcc/function.c
> @@ -82,6 +82,8 @@ along with GCC; see the file COPYING3.  If not see
>   #include "gimple.h"
>   #include "options.h"
>   #include "function-abi.h"
> +#include "value-range.h"
> +#include "gimple-range.h"
>   
>   /* So we can assign to cfun in this file.  */
>   #undef cfun
> @@ -4856,6 +4858,8 @@ allocate_struct_function (tree fndecl, bool abstract_p)
>        binding annotations among them.  */
>     cfun->debug_nonbind_markers = lang_hooks.emits_begin_stmt
>       && MAY_HAVE_DEBUG_MARKER_STMTS;
> +
> +  cfun->x_range_query = &global_ranges;
>   }
>   
>   /* This is like allocate_struct_function, but pushes a new cfun for FNDECL
> diff --git a/gcc/function.h b/gcc/function.h
> index 66cfa973808..41b446bfe7c 100644
> --- a/gcc/function.h
> +++ b/gcc/function.h
> @@ -157,6 +157,7 @@ struct GTY(()) rtl_eh {
>   struct gimple_df;
>   struct call_site_record_d;
>   struct dw_fde_node;
> +class range_query;
>   
>   struct GTY(()) varasm_status {
>     /* If we're using a per-function constant pool, this is it.  */
> @@ -309,6 +310,11 @@ struct GTY(()) function {
>        debugging is enabled.  */
>     struct dw_fde_node *fde;
>   
> +  /* Range query mechanism for functions.  The default is to pick up
> +     global ranges.  If a pass wants on-demand ranges OTOH, it must
> +     call enable/disable_ranger().  */
> +  range_query * GTY ((skip)) x_range_query;
> +

Mostly out of curiosity: why the 'x_' prefix?  (I'm used to seeing
that in the expansion of the option macros but it seems out of place
here.)

>     /* Last statement uid.  */
>     int last_stmt_uid;
>   
> @@ -712,4 +718,14 @@ extern const char *current_function_name (void);
>   
>   extern void used_types_insert (tree);
>   
> +extern range_query *get_global_range_query ();
> +
> +// Returns the currently active range access class.  This is meant to be used
> +// with the `class range_query' API.  When there is no active range class,
> +// global ranges are used.
> +#define RANGE_QUERY(fun) (fun)->x_range_query
> +
> +// As above, but for accessing global ranges between passes.
> +#define GLOBAL_RANGE_QUERY get_global_range_query ()

Unless there's some reason that escapes me, could these be functions
(possibly defined inline) rather than macros?  (They're a lot easier
to work with, such as when I want to trace calls in some way.)

> +
>   #endif  /* GCC_FUNCTION_H */
> diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
> index 2c922e32913..c645d15f5af 100644
> --- a/gcc/gimple-range-cache.cc
> +++ b/gcc/gimple-range-cache.cc
> @@ -384,7 +384,6 @@ block_range_cache::dump (FILE *f, basic_block bb, bool print_varying)
>   ssa_global_cache::ssa_global_cache ()
>   {
>     m_tab.create (0);
> -  m_tab.safe_grow_cleared (num_ssa_names);
>     m_irange_allocator = new irange_allocator;
>   }
>   
> diff --git a/gcc/gimple-range.cc b/gcc/gimple-range.cc
> index 710bc7f9632..4e1aeee8ed0 100644
> --- a/gcc/gimple-range.cc
> +++ b/gcc/gimple-range.cc
> @@ -1402,3 +1402,133 @@ trace_ranger::range_of_expr (irange &r, tree name, gimple *s)
>   
>     return trailer (idx, "range_of_expr", res, name, r);
>   }
> +
> +// Return the legacy global range for NAME if it has one, otherwise
> +// return VARYING.

I realize this is just being moved from elsewhere but I would suggest
to take this opportunity and also document the effects on the range
argument.

> +
> +static void
> +get_range_global (irange &r, tree name)
> +{
> +  tree type = TREE_TYPE (name);
> +
> +  if (SSA_NAME_IS_DEFAULT_DEF (name))
> +    {
> +      tree sym = SSA_NAME_VAR (name);
> +      // Adapted from vr_values::get_lattice_entry().
> +      // Use a range from an SSA_NAME's available range.
> +      if (TREE_CODE (sym) == PARM_DECL)
> +	{
> +	  // Try to use the "nonnull" attribute to create ~[0, 0]
> +	  // anti-ranges for pointers.  Note that this is only valid with
> +	  // default definitions of PARM_DECLs.
> +	  if (POINTER_TYPE_P (type)
> +	      && ((cfun && nonnull_arg_p (sym)) || get_ptr_nonnull (name)))
> +	    r.set_nonzero (type);
> +	  else if (INTEGRAL_TYPE_P (type))
> +	    {
> +	      get_range_info (name, r);
> +	      if (r.undefined_p ())
> +		r.set_varying (type);
> +	    }
> +	  else
> +	    r.set_varying (type);
> +	}
> +      // If this is a local automatic with no definition, use undefined.
> +      else if (TREE_CODE (sym) != RESULT_DECL)
> +	r.set_undefined ();
> +      else
> +	r.set_varying (type);
> +   }
> +  else if (!POINTER_TYPE_P (type) && SSA_NAME_RANGE_INFO (name))
> +    {
> +      get_range_info (name, r);
> +      if (r.undefined_p ())
> +	r.set_varying (type);
> +    }
> +  else if (POINTER_TYPE_P (type) && SSA_NAME_PTR_INFO (name))
> +    {
> +      if (get_ptr_nonnull (name))
> +	r.set_nonzero (type);
> +      else
> +	r.set_varying (type);
> +    }
> +  else
> +    r.set_varying (type);
> +}
> +
> +// ?? Like above, but only for default definitions of NAME. 

I couldn't help but notice another variation on the dubious ???
yet wide-spread convention:
   https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570442.html

> This is
> +// so VRP passes using ranger do not start with known ranges,
> +// otherwise we'd eliminate builtin_unreachables too early because of
> +// inlining.
> +//
> +// Without this restriction, the test in g++.dg/tree-ssa/pr61034.C has
> +// all of its unreachable calls removed too early.  We should
> +// investigate whether we should just adjust the test above.
> +
> +value_range
> +gimple_range_global (tree name)
> +{
> +  gcc_checking_assert (gimple_range_ssa_p (name));
> +  tree type = TREE_TYPE (name);
> +
> +  if (SSA_NAME_IS_DEFAULT_DEF (name))
> +    {
> +      value_range vr;
> +      get_range_global (vr, name);
> +      return vr;
> +    }
> +  return value_range (type);
> +}
> +
> +// ----------------------------------------------
> +// global_range_query implementation.
> +
> +global_range_query global_ranges;
> +
> +range_query *
> +get_global_range_query ()
> +{
> +  if (cfun)
> +    return RANGE_QUERY (cfun);
> +
> +  return &global_ranges;
> +}
> +
> +bool
> +global_range_query::range_of_expr (irange &r, tree expr, gimple *)
> +{
> +  tree type = TREE_TYPE (expr);
> +
> +  if (!irange::supports_type_p (type) || !gimple_range_ssa_p (expr))
> +    return get_tree_range (r, expr);
> +
> +  get_range_global (r, expr);
> +
> +  return true;
> +}
> +
> +void
> +enable_ranger ()
> +{
> +  gimple_ranger *r;
> +
> +  if (param_evrp_mode & EVRP_MODE_TRACE)
> +    r = new trace_ranger;
> +  else
> +    r = new gimple_ranger;
> +
> +  RANGE_QUERY (cfun) = r;
> +}
> +
> +void
> +disable_ranger (bool export_ranges)
> +{
> +  gimple_ranger *r = (gimple_ranger *) RANGE_QUERY (cfun);
> +
> +  if (export_ranges)
> +    r->export_global_ranges ();
> +
> +  delete r;

The above is a downcast from range_query*, so if the instance is
something else the code won't work correctly and might crash,
right?  Or it might call the wrong function/dtor.  Should there
be a check of some sort to make sure that doesn't happen?

Martin

> +
> +  RANGE_QUERY (cfun) = &global_ranges;
> +}
> diff --git a/gcc/gimple-range.h b/gcc/gimple-range.h
> index f33156181bf..1ba073820a6 100644
> --- a/gcc/gimple-range.h
> +++ b/gcc/gimple-range.h
> @@ -53,7 +53,7 @@ public:
>     virtual void range_on_entry (irange &r, basic_block bb, tree name);
>     virtual void range_on_exit (irange &r, basic_block bb, tree name);
>     void export_global_ranges ();
> -  void dump (FILE *f);
> +  virtual void dump (FILE *f) OVERRIDE;
>   protected:
>     bool calc_stmt (irange &r, gimple *s, tree name = NULL_TREE);
>     bool range_of_range_op (irange &r, gimple *s);
> @@ -130,50 +130,6 @@ range_compatible_p (tree type1, tree type2)
>   	  && TYPE_SIGN (type1) == TYPE_SIGN (type2));
>   }
>   
> -// Return the legacy GCC global range for NAME if it has one, otherwise
> -// return VARYING.
> -
> -static inline value_range
> -gimple_range_global (tree name)
> -{
> -  gcc_checking_assert (gimple_range_ssa_p (name));
> -  tree type = TREE_TYPE (name);
> -
> -  if (SSA_NAME_IS_DEFAULT_DEF (name))
> -    {
> -      tree sym = SSA_NAME_VAR (name);
> -      // Adapted from vr_values::get_lattice_entry().
> -      // Use a range from an SSA_NAME's available range.
> -      if (TREE_CODE (sym) == PARM_DECL)
> -	{
> -	  // Try to use the "nonnull" attribute to create ~[0, 0]
> -	  // anti-ranges for pointers.  Note that this is only valid with
> -	  // default definitions of PARM_DECLs.
> -	  if (POINTER_TYPE_P (type)
> -	      && (nonnull_arg_p (sym) || get_ptr_nonnull (name)))
> -	    {
> -	      value_range r;
> -	      r.set_nonzero (type);
> -	      return r;
> -	    }
> -	  else if (INTEGRAL_TYPE_P (type))
> -	    {
> -	      value_range r;
> -	      get_range_info (name, r);
> -	      if (r.undefined_p ())
> -		r.set_varying (type);
> -	      return r;
> -	    }
> -	}
> -      // If this is a local automatic with no definition, use undefined.
> -      else if (TREE_CODE (sym) != RESULT_DECL)
> -	return value_range ();
> -   }
> -  // Otherwise return range for the type.
> -  return value_range (type);
> -}
> -
> -
>   // This class overloads the ranger routines to provide tracing facilties
>   // Entry and exit values to each of the APIs is placed in the dumpfile.
>   
> @@ -202,4 +158,18 @@ private:
>   // Temporary external interface to share with vr_values.
>   bool range_of_builtin_call (range_query &query, irange &r, gcall *call);
>   
> +// Global ranges for SSA names using SSA_NAME_RANGE_INFO.
> +
> +class global_range_query : public range_query
> +{
> +public:
> +  bool range_of_expr (irange &r, tree expr, gimple * = NULL) OVERRIDE;
> +};
> +
> +extern global_range_query global_ranges;
> +extern value_range gimple_range_global (tree name);
> +
> +extern void enable_ranger ();
> +extern void disable_ranger (bool export_ranges = true);
> +
>   #endif // GCC_GIMPLE_RANGE_STMT_H
> diff --git a/gcc/gimple-ssa-evrp.c b/gcc/gimple-ssa-evrp.c
> index 5f566ae0958..829fdcdaef2 100644
> --- a/gcc/gimple-ssa-evrp.c
> +++ b/gcc/gimple-ssa-evrp.c
> @@ -60,7 +60,7 @@ public:
>       if (dump_file)
>         {
>   	fprintf (dump_file, "\nValue ranges after Early VRP:\n\n");
> -	m_range_analyzer.dump_all_value_ranges (dump_file);
> +	m_range_analyzer.dump (dump_file);
>   	fprintf (dump_file, "\n");
>         }
>     }
> diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
> index 12e6e6f3e22..b0f1c47f05c 100644
> --- a/gcc/tree-vrp.c
> +++ b/gcc/tree-vrp.c
> @@ -4044,7 +4044,7 @@ vrp_prop::finalize ()
>     if (dump_file)
>       {
>         fprintf (dump_file, "\nValue ranges after VRP:\n\n");
> -      m_vr_values->dump_all_value_ranges (dump_file);
> +      m_vr_values->dump (dump_file);
>         fprintf (dump_file, "\n");
>       }
>   
> diff --git a/gcc/value-query.cc b/gcc/value-query.cc
> index 4bb0897c446..509d2d33cc5 100644
> --- a/gcc/value-query.cc
> +++ b/gcc/value-query.cc
> @@ -135,6 +135,11 @@ range_query::value_of_stmt (gimple *stmt, tree name)
>   
>   }
>   
> +void
> +range_query::dump (FILE *)
> +{
> +}
> +
>   // valuation_query support routines for value_range_equiv's.
>   
>   class equiv_allocator : public object_allocator<value_range_equiv>
> diff --git a/gcc/value-query.h b/gcc/value-query.h
> index e2cbc6852b0..5eff9317ed5 100644
> --- a/gcc/value-query.h
> +++ b/gcc/value-query.h
> @@ -95,6 +95,7 @@ public:
>     // rewrite all uses of it to the above API.
>     virtual const class value_range_equiv *get_value_range (const_tree,
>   							  gimple * = NULL);
> +  virtual void dump (FILE *);
>   
>   protected:
>     class value_range_equiv *allocate_value_range_equiv ();
> diff --git a/gcc/vr-values.c b/gcc/vr-values.c
> index b1bf53af9e0..a89f0b646ae 100644
> --- a/gcc/vr-values.c
> +++ b/gcc/vr-values.c
> @@ -1819,7 +1819,7 @@ vr_values::adjust_range_with_scev (value_range_equiv *vr, class loop *loop,
>   /* Dump value ranges of all SSA_NAMEs to FILE.  */
>   
>   void
> -vr_values::dump_all_value_ranges (FILE *file)
> +vr_values::dump (FILE *file)
>   {
>     size_t i;
>   
> diff --git a/gcc/vr-values.h b/gcc/vr-values.h
> index 8c1b2e0a292..81b9131f7f1 100644
> --- a/gcc/vr-values.h
> +++ b/gcc/vr-values.h
> @@ -116,7 +116,7 @@ class vr_values : public range_query
>     tree op_with_constant_singleton_value_range (tree);
>     void adjust_range_with_scev (value_range_equiv *, class loop *,
>   			       gimple *, tree);
> -  void dump_all_value_ranges (FILE *);
> +  virtual void dump (FILE *) OVERRIDE;
>   
>     void extract_range_for_var_from_comparison_expr (tree, enum tree_code,
>   						   tree, tree,
>