On Mon, Jul 26, 2021 at 4:18 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Aldy Hernandez <al...@redhat.com> writes:
> > This patch replaces the evrp_range_analyzer in the loop versioning code
> > with an on-demand ranger.
> >
> > Everything was pretty straightforward, except that range_of_expr requires
> > a gimple statement as context to provide context aware ranges.  I didn't see
> > a convient place where the statement was saved, so I made a vector indexed
> > by SSA names.  As an alternative, I tried to use the loop's first statement,
> > but that proved to be insufficient.
>
> The mapping is one-to-many though: there can be multiple statements
> for each SSA name.  Maybe that doesn't matter in this context and
> any of the statements can act as a representative.
>
> I'm surprised that the loop's first statement didn't work though,
> since the SSA name is supposedly known to be loop-invariant.  What went
> wrong when you tried that?

I was looking at the first statement of loop_info->block_list and one
of the dg.exp=loop-versioning* tests failed.  Perhaps I should have
used the loop itself, as in the attached patch.  With this patch all
of the loop-versioning tests pass.

>
> > I am not familiar with loop versioning, but if the DOM walk was only
> > necessary for the calls to record_ranges_from_stmt, this too could be
> > removed as the ranger will work without it.
>
> Yeah, that was the only reason.  If the information is available at
> version_for_unity (I guess it is) then we should just avoid recording
> the versioning there if so.
>
> How expensive is the check?  If the result is worth caching, perhaps
> we should have two bitmaps: the existing one, and one that records
> whether we've checked a particular SSA name.
>
> If the check is relatively cheap then that won't be worth it though.

If you're asking about the range_of_expr check, that's all cached, so
it should be pretty cheap.  Besides, we're no longer calculating
ranges for each statement in the IL, as we were doing in lv_dom_walker
with evrp's record_ranges_from_stmt.  Only statements of interest are
queried.

How about this patch, pending tests?

Aldy
From 8a350003d950869499d729921008abdb491d3a5e Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <al...@redhat.com>
Date: Sat, 24 Jul 2021 12:29:28 +0200
Subject: [PATCH] Replace evrp use in loop versioning with ranger.

This patch replaces the evrp_range_analyzer in the loop versioning code
with an on-demand ranger.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-loop-versioning.cc (lv_dom_walker::lv_dom_walker): Remove
	use of m_range_analyzer.
	(loop_versioning::lv_dom_walker::before_dom_children): Same.
	(loop_versioning::lv_dom_walker::after_dom_children): Remove.
	(loop_versioning::prune_loop_conditions): Replace vr_values use
	with range_query interface.
	(pass_loop_versioning::execute): Use ranger.
---
 gcc/gimple-loop-versioning.cc | 44 ++++++++++++-----------------------
 1 file changed, 15 insertions(+), 29 deletions(-)

diff --git a/gcc/gimple-loop-versioning.cc b/gcc/gimple-loop-versioning.cc
index 4b70c5a4aab..46c3a508c8d 100644
--- a/gcc/gimple-loop-versioning.cc
+++ b/gcc/gimple-loop-versioning.cc
@@ -30,19 +30,17 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-ssa-loop.h"
 #include "ssa.h"
 #include "tree-scalar-evolution.h"
-#include "tree-chrec.h"
 #include "tree-ssa-loop-ivopts.h"
 #include "fold-const.h"
 #include "tree-ssa-propagate.h"
 #include "tree-inline.h"
 #include "domwalk.h"
-#include "alloc-pool.h"
-#include "vr-values.h"
-#include "gimple-ssa-evrp-analyze.h"
 #include "tree-vectorizer.h"
 #include "omp-general.h"
 #include "predict.h"
 #include "tree-into-ssa.h"
+#include "gimple-range.h"
+#include "tree-cfg.h"
 
 namespace {
 
@@ -261,14 +259,10 @@ private:
     lv_dom_walker (loop_versioning &);
 
     edge before_dom_children (basic_block) FINAL OVERRIDE;
-    void after_dom_children (basic_block) FINAL OVERRIDE;
 
   private:
     /* The parent pass.  */
     loop_versioning &m_lv;
-
-    /* Used to build context-dependent range information.  */
-    evrp_range_analyzer m_range_analyzer;
   };
 
   /* Used to simplify statements based on conditions that are established
@@ -308,7 +302,7 @@ private:
   bool analyze_block (basic_block);
   bool analyze_blocks ();
 
-  void prune_loop_conditions (class loop *, vr_values *);
+  void prune_loop_conditions (class loop *);
   bool prune_conditions ();
 
   void merge_loop_info (class loop *, class loop *);
@@ -500,7 +494,7 @@ loop_info::worth_versioning_p () const
 }
 
 loop_versioning::lv_dom_walker::lv_dom_walker (loop_versioning &lv)
-  : dom_walker (CDI_DOMINATORS), m_lv (lv), m_range_analyzer (false)
+  : dom_walker (CDI_DOMINATORS), m_lv (lv)
 {
 }
 
@@ -509,26 +503,12 @@ loop_versioning::lv_dom_walker::lv_dom_walker (loop_versioning &lv)
 edge
 loop_versioning::lv_dom_walker::before_dom_children (basic_block bb)
 {
-  m_range_analyzer.enter (bb);
-
   if (bb == bb->loop_father->header)
-    m_lv.prune_loop_conditions (bb->loop_father, &m_range_analyzer);
-
-  for (gimple_stmt_iterator si = gsi_start_bb (bb); !gsi_end_p (si);
-       gsi_next (&si))
-    m_range_analyzer.record_ranges_from_stmt (gsi_stmt (si), false);
+    m_lv.prune_loop_conditions (bb->loop_father);
 
   return NULL;
 }
 
-/* Process BB after processing the blocks it dominates.  */
-
-void
-loop_versioning::lv_dom_walker::after_dom_children (basic_block bb)
-{
-  m_range_analyzer.leave (bb);
-}
-
 /* Decide whether to replace VAL with a new value in a versioned loop.
    Return the new value if so, otherwise return null.  */
 
@@ -1483,18 +1463,21 @@ loop_versioning::analyze_blocks ()
    LOOP.  */
 
 void
-loop_versioning::prune_loop_conditions (class loop *loop, vr_values *vrs)
+loop_versioning::prune_loop_conditions (class loop *loop)
 {
   loop_info &li = get_loop_info (loop);
 
   int to_remove = -1;
   bitmap_iterator bi;
   unsigned int i;
+  int_range_max r;
   EXECUTE_IF_SET_IN_BITMAP (&li.unity_names, 0, i, bi)
     {
       tree name = ssa_name (i);
-      const value_range_equiv *vr = vrs->get_value_range (name);
-      if (vr && !vr->may_contain_p (build_one_cst (TREE_TYPE (name))))
+      gimple *stmt = first_stmt (loop->header);
+
+      if (get_range_query (cfun)->range_of_expr (r, name, stmt)
+	  && !r.contains_p (build_one_cst (TREE_TYPE (name))))
 	{
 	  if (dump_enabled_p ())
 	    dump_printf_loc (MSG_NOTE, find_loop_location (loop),
@@ -1810,7 +1793,10 @@ pass_loop_versioning::execute (function *fn)
   if (number_of_loops (fn) <= 1)
     return 0;
 
-  return loop_versioning (fn).run ();
+  enable_ranger (fn);
+  unsigned int ret = loop_versioning (fn).run ();
+  disable_ranger (fn);
+  return ret;
 }
 
 } // anon namespace
-- 
2.31.1

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