Re: Do not leak memory when streaming in ssa names

[Jan Hubicka <hubicka@ucw.cz>]

> On Mon, 23 Nov 2020, Jan Hubicka wrote:
> 
> > > On Mon, 23 Nov 2020, Jan Hubicka wrote:
> > > 
> > > > Hi,
> > > > tree-streamer-in currently calls init_tree_ssa that calls init_ssanames
> > > > that allocates space in ssa_names array for 50 names.  Later it streams
> > > > in the count and calls init_tree_ssa again, this time with correct
> > > > count, which is rounded up to 50 and allocated again leaking the first
> > > > array.
> > > > 
> > > > This patch fixes it by adding extra argument to init_tree_ssa specifing
> > > > whether ssa names should be initialized.  There are few places where we
> > > > initialize ssa and only lto streaming is special, so i think extra arg
> > > > works well here.
> > > > 
> > > > I am not quite sure about the 50MB default.  I think it was made before
> > > > ggc_free was implemented (so resizing vectors was expensive) and when we
> > > > had only one function in SSA form at a time.  Most of functions in C++
> > > > will probably need fewer than 50 SSA names until inlining.
> > > > 
> > > > This saves 21MB of WPA linking libxul.
> > > 
> > > Why do we input SSA names at WPA?
> > 
> > To ICF compare function bodies. It tends to load tons of small bodies.
> > We also may load body when merging BB profile etc.
> > > 
> > > > Bootstrapping/regtesting x86_64-linux, OK if it suceeds?
> > > 
> > > I think calling init_ssanames again is bogus.  Please simply
> > > do that in input_ssa_names after we know how many we need
> > > adding a number of SSA names to reserve argument to init_tree_ssa
> > > and passing that down instead.
> > 
> > I tried that originally but it hit ICE in init_ssa_operands.  Seems that
> > reloacating them is last change I need though.  Does this look better?
> 
> Patch below looks completely unrelated but is OK as well if it passes
> testing ;)

Glad to hear since it is in mainline for a while :)
Here is correct pathc. Sorry.

	* lto-streamer-in.c (input_cfg): Do not init ssa operands.
	(input_function): Do not init tree_ssa and set in_ssa_p.
	(input_ssa_names): Do it here.
	* tree-ssa.c (init_tree_ssa): Add additional SIZE parameter, default
	to 0
	* tree-ssanames.c (init_ssanames): Do not round size up to 50, allocate
	precisely.
diff --git a/gcc/lto-streamer-in.c b/gcc/lto-streamer-in.c
index 64037f74ad3..a20d64b0089 100644
--- a/gcc/lto-streamer-in.c
+++ b/gcc/lto-streamer-in.c
@@ -1017,7 +1017,6 @@ input_cfg (class lto_input_block *ib, class data_in *data_in,
   int index;
 
   init_empty_tree_cfg_for_function (fn);
-  init_ssa_operands (fn);
 
   profile_status_for_fn (fn) = streamer_read_enum (ib, profile_status_d,
 						   PROFILE_LAST);
@@ -1144,7 +1143,9 @@ input_ssa_names (class lto_input_block *ib, class data_in *data_in,
   unsigned int i, size;
 
   size = streamer_read_uhwi (ib);
-  init_ssanames (fn, size);
+  init_tree_ssa (fn, size);
+  cfun->gimple_df->in_ssa_p = true;
+  init_ssa_operands (fn);
 
   i = streamer_read_uhwi (ib);
   while (i)
@@ -1384,9 +1385,6 @@ input_function (tree fn_decl, class data_in *data_in,
 
   push_struct_function (fn_decl);
   fn = DECL_STRUCT_FUNCTION (fn_decl);
-  init_tree_ssa (fn);
-  /* We input IL in SSA form.  */
-  cfun->gimple_df->in_ssa_p = true;
 
   gimple_register_cfg_hooks ();
 
diff --git a/gcc/tree-ssa.c b/gcc/tree-ssa.c
index b44361f8244..24a5154620d 100644
--- a/gcc/tree-ssa.c
+++ b/gcc/tree-ssa.c
@@ -1218,15 +1218,16 @@ err:
 #  pragma GCC diagnostic pop
 #endif
 
-/* Initialize global DFA and SSA structures.  */
+/* Initialize global DFA and SSA structures.
+   If SIZE is non-zero allocated ssa names array of a given size.  */
 
 void
-init_tree_ssa (struct function *fn)
+init_tree_ssa (struct function *fn, int size)
 {
   fn->gimple_df = ggc_cleared_alloc<gimple_df> ();
   fn->gimple_df->default_defs = hash_table<ssa_name_hasher>::create_ggc (20);
   pt_solution_reset (&fn->gimple_df->escaped);
-  init_ssanames (fn, 0);
+  init_ssanames (fn, size);
 }
 
 /* Deallocate memory associated with SSA data structures for FNDECL.  */
diff --git a/gcc/tree-ssanames.c b/gcc/tree-ssanames.c
index 6ac97fe39c4..ec4681f85cb 100644
--- a/gcc/tree-ssanames.c
+++ b/gcc/tree-ssanames.c
@@ -77,10 +77,10 @@ unsigned int ssa_name_nodes_created;
 void
 init_ssanames (struct function *fn, int size)
 {
-  if (size < 50)
-    size = 50;
-
-  vec_alloc (SSANAMES (fn), size);
+  if (!size)
+    vec_alloc (SSANAMES (fn), 50);
+  else
+    vec_safe_reserve (SSANAMES (fn), size, true);
 
   /* Version 0 is special, so reserve the first slot in the table.  Though
      currently unused, we may use version 0 in alias analysis as part of