[PATCH]ira: recompute regstat as max_regno changes [PR97705]

["Kewen.Lin" <linkw@linux.ibm.com>]

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Hi,

As PR97705 shows, my commit r11-4637 caused some dumping
comparison difference error on pass ira.  It exposed one
issue about the newly introduced function remove_scratches,
which can increase the largest pseudo reg number if it
succeeds, later some function will use the max_reg_num()
to get the latest max_regno, when iterating the numbers
we can access some data structures which are allocated as
the previous max_regno, some out of array bound accesses
can occur, the failure can be random since the values
beyond the array could be random.

This patch is to free/reinit/recompute the relevant data
structures that is regstat_n_sets_and_refs and reg_info_p
to ensure we won't access beyond some array bounds.

Bootstrapped/regtested on powerpc64le-linux-gnu P9 and
powerpc64-linux-gnu P8.

Any thoughts?  Is it a reasonable fix?

BR,
Kewen
-----
gcc/ChangeLog:

	PR rtl-optimization/97705
	* ira.c (ira): Refactor some regstat free/init/compute invocation
	into lambda function regstat_recompute_for_max_regno, and call it
	when max_regno increases as remove_scratches succeeds.

[-- Attachment #2: ira_recomp.diff --]
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diff --git a/gcc/ira.c b/gcc/ira.c
index 050405f1833..5443031674e 100644
--- a/gcc/ira.c
+++ b/gcc/ira.c
@@ -5526,8 +5526,26 @@ ira (FILE *f)
   end_alias_analysis ();
   free (reg_equiv);
 
+  /* Once max_regno changes, we need to free and re-init/re-compute
+     some data structures like regstat_n_sets_and_refs and reg_info_p.  */
+  auto regstat_recompute_for_max_regno = []() {
+    regstat_free_n_sets_and_refs ();
+    regstat_free_ri ();
+    regstat_init_n_sets_and_refs ();
+    regstat_compute_ri ();
+  };
+
+  int max_regno_before_rm = max_reg_num ();
   if (ira_use_lra_p && remove_scratches ())
-    ira_expand_reg_equiv ();
+    {
+      ira_expand_reg_equiv ();
+      /* For now remove_scatches is supposed to create pseudos when it
+	 succeeds, assert this happens all the time.  Once it doesn't
+	 hold, we should guard the regstat recompute for the case
+	 max_regno changes.  */
+      gcc_assert (max_regno_before_rm != max_reg_num ());
+      regstat_recompute_for_max_regno ();
+    }
 
   if (resize_reg_info () && flag_ira_loop_pressure)
     ira_set_pseudo_classes (true, ira_dump_file);
@@ -5654,12 +5672,7 @@ ira (FILE *f)
 #endif
 
   if (max_regno != max_regno_before_ira)
-    {
-      regstat_free_n_sets_and_refs ();
-      regstat_free_ri ();
-      regstat_init_n_sets_and_refs ();
-      regstat_compute_ri ();
-    }
+    regstat_recompute_for_max_regno ();
 
   overall_cost_before = ira_overall_cost;
   if (! ira_conflicts_p)