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Re: [PATCH] DWARF: Don't expand hash table when no insert is needed


On Mon, Dec 17, 2018 at 2:00 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Sun, Dec 16, 2018 at 9:33 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > find_slot_with_hash has
> >
> >  if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
> >     expand ();
> >
> > which may expand hash table even if no insert is neeed and change hash
> > table traverse order.  When output_macinfo_op is called, all index
> > strings have been added to hash table by save_macinfo_strings, we
> > shouldn't expand index string hash table.  Otherwise find_slot_with_hash
> > will expand hash table when hash table has the right size.
>
> So the point is that output_macinfo_op is called from code traversing the
> hashtable?  I didn't really manage to quickly spot that.
>
> > Tested on i686 and x86-64.  OK for trunk?
>
> OK if called from htab traverse (please clarify that in the comment you add).
>
> Richard.

dwarf2out_finish performs:

1. save_macinfo_strings
2. hash table traverse of index_string
3. output_macinfo -> output_macinfo_op
4. output_indirect_strings -> hash table traverse of output_index_string

find_slot_with_hash has

 if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
    expand ();

which may expand hash table even if no insertion is neeed and change hash
table traverse order.  When output_macinfo_op is called, all index strings
have been added to hash table by save_macinfo_strings and we shouldn't
expand index string hash table.  Otherwise find_slot_with_hash will expand
hash table when hash table has the right size and hash table traverse of
output_index_string will have a different traverse order from index_string.

This is the updated patch I am checking in.

-- 
H.J.
From 18caa0346c36e4e6a9d556d5a1256f6dc99e8598 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sun, 16 Dec 2018 10:12:01 -0800
Subject: [PATCH] DWARF: Don't expand hash table when no insertion is needed

dwarf2out_finish performs:

1. save_macinfo_strings
2. hash table traverse of index_string
3. output_macinfo -> output_macinfo_op
4. output_indirect_strings -> hash table traverse of output_index_string

find_slot_with_hash has

 if (insert == INSERT && m_size * 3 <= m_n_elements * 4)
    expand ();

which may expand hash table even if no insertion is neeed and change hash
table traverse order.  When output_macinfo_op is called, all index strings
have been added to hash table by save_macinfo_strings and we shouldn't
expand index string hash table.  Otherwise find_slot_with_hash will expand
hash table when hash table has the right size and hash table traverse of
output_index_string will have a different traverse order from index_string.

	PR debug/79342
	* dwarf2out.c (find_AT_string_in_table): Add insert argument
	defaulting to INSERT and replace INSERT.
	(find_AT_string): Likewise.
	(output_macinfo_op): Pass NO_INSERT to find_AT_string.
---
 gcc/dwarf2out.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index b2381056991..49d8a0af33b 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -4618,12 +4618,13 @@ indirect_string_hasher::equal (indirect_string_node *x1, const char *x2)
 
 static struct indirect_string_node *
 find_AT_string_in_table (const char *str,
-			 hash_table<indirect_string_hasher> *table)
+			 hash_table<indirect_string_hasher> *table,
+			 enum insert_option insert = INSERT)
 {
   struct indirect_string_node *node;
 
   indirect_string_node **slot
-    = table->find_slot_with_hash (str, htab_hash_string (str), INSERT);
+    = table->find_slot_with_hash (str, htab_hash_string (str), insert);
   if (*slot == NULL)
     {
       node = ggc_cleared_alloc<indirect_string_node> ();
@@ -4640,12 +4641,12 @@ find_AT_string_in_table (const char *str,
 /* Add STR to the indirect string hash table.  */
 
 static struct indirect_string_node *
-find_AT_string (const char *str)
+find_AT_string (const char *str, enum insert_option insert = INSERT)
 {
   if (! debug_str_hash)
     debug_str_hash = hash_table<indirect_string_hasher>::create_ggc (10);
 
-  return find_AT_string_in_table (str, debug_str_hash);
+  return find_AT_string_in_table (str, debug_str_hash, insert);
 }
 
 /* Add a string attribute value to a DIE.  */
@@ -28095,7 +28096,19 @@ output_macinfo_op (macinfo_entry *ref)
       break;
     case DW_MACRO_define_strp:
     case DW_MACRO_undef_strp:
-      node = find_AT_string (ref->info);
+      /* NB: dwarf2out_finish performs:
+	   1. save_macinfo_strings
+	   2. hash table traverse of index_string
+	   3. output_macinfo -> output_macinfo_op
+	   4. output_indirect_strings
+		-> hash table traverse of output_index_string
+
+         When output_macinfo_op is called, all index strings have been
+	 added to hash table by save_macinfo_strings and we can't pass
+	 INSERT to find_slot_with_hash which may expand hash table, even
+	 if no insertion is needed, and change hash table traverse order
+	 between index_string and output_index_string.  */
+      node = find_AT_string (ref->info, NO_INSERT);
       gcc_assert (node
 		  && (node->form == DW_FORM_strp
 		      || node->form == dwarf_FORM (DW_FORM_strx)));
-- 
2.19.2


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