Add obstack for canonical file name hash table

[Richard Biener]

On Tue, 5 Nov 2019, Jan Hubicka wrote:

> Hi,
> looking into malloc overhead I noticed that we do a lot of small
> allocations to hold file names comming from location info. This patch
> puts it into an obstack so it interleaves memory allocated by scc_hash
> less frequently.
> (Still we end up interleaving 64k pages which are permanent - in fact
> this table seems to leak from WPA and temporary during stream in)
> 
> Bootstrapped/regtested x86_64-linux. OK?

I think the obstack deserves a big fat comment that it cannot be
reclaimed since the linemap retains permanent pointers into it.
That also suggests to put the string_slot into a separate obstack
or better, make the hasher (and other string_slot hashers)
embed the string_slot struct in the hash?  We'd save an allocation
everywhere.

Richard.

> Honza
> 
> 	* lto-streamer-in.c (file_name_obstack): New obstack.
> 	(canon_file_name): Use it.
> 	(lto_reader_init): Initialize it.
> Index: lto-streamer-in.c
> ===================================================================
> --- lto-streamer-in.c	(revision 277796)
> +++ lto-streamer-in.c	(working copy)
> @@ -57,6 +57,7 @@ freeing_string_slot_hasher::remove (valu
>  
>  /* The table to hold the file names.  */
>  static hash_table<freeing_string_slot_hasher> *file_name_hash_table;
> +static struct obstack file_name_obstack;
>  
>  
>  /* Check that tag ACTUAL has one of the given values.  NUM_TAGS is the
> @@ -113,8 +114,9 @@ canon_file_name (const char *string)
>        char *saved_string;
>        struct string_slot *new_slot;
>  
> -      saved_string = (char *) xmalloc (len + 1);
> -      new_slot = XCNEW (struct string_slot);
> +      saved_string = XOBNEWVEC (&file_name_obstack, char, len + 1);
> +      new_slot = XOBNEWVAR (&file_name_obstack,
> +			    struct string_slot, sizeof (struct string_slot));
>        memcpy (saved_string, string, len + 1);
>        new_slot->s = saved_string;
>        new_slot->len = len;
> @@ -1723,6 +1725,7 @@ lto_reader_init (void)
>    lto_streamer_init ();
>    file_name_hash_table
>      = new hash_table<freeing_string_slot_hasher> (37);
> +  gcc_obstack_init (&file_name_obstack);
>  }
>  
>  
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)