Re: The performance data for two different implementation of new security feature -ftrivial-auto-var-init

[Qing Zhao <qing.zhao@oracle.com>]

Hi,

With the following patch:

[qinzhao@localhost gcc]$ git diff tree-ssa-structalias.c
diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
index cf653be..bd18841 100644
--- a/gcc/tree-ssa-structalias.c
+++ b/gcc/tree-ssa-structalias.c
@@ -4851,6 +4851,30 @@ find_func_aliases_for_builtin_call (struct function *fn, gcall *t)
   return false;
 }
 
+static void
+find_func_aliases_for_deferred_init (gcall *t)
+{
+  
+  tree lhsop = gimple_call_lhs (t);
+  enum auto_init_type init_type
+    = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (t, 1));
+  auto_vec<ce_s, 2> lhsc;
+  auto_vec<ce_s, 4> rhsc;
+  struct constraint_expr temp;
+ 
+  get_constraint_for (lhsop, &lhsc);
+  if (init_type == AUTO_INIT_ZERO && flag_delete_null_pointer_checks)
+    temp.var = nothing_id;
+  else
+    temp.var = nonlocal_id;
+  temp.type = ADDRESSOF;
+  temp.offset = 0;
+  rhsc.safe_push (temp);
+
+  process_all_all_constraints (lhsc, rhsc);
+  return;
+}
+
 /* Create constraints for the call T.  */
 
 static void
@@ -4864,6 +4888,12 @@ find_func_aliases_for_call (struct function *fn, gcall *t)
       && find_func_aliases_for_builtin_call (fn, t))
     return;
 
+  if (gimple_call_internal_p (t, IFN_DEFERRED_INIT))
+    {
+      find_func_aliases_for_deferred_init (t);
+      return;
+    }
+

The *.ealias dump for the routine “bump_map” are exactly the same for approach A and D. 
However, the stack size for D still bigger than A. 

Any suggestions?

Qing


On Feb 2, 2021, at 9:17 AM, Qing Zhao via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> 
> 
>> On Feb 2, 2021, at 1:43 AM, Richard Biener <rguenther@suse.de> wrote:
>> 
>> On Mon, 1 Feb 2021, Qing Zhao wrote:
>> 
>>> Hi, Richard,
>>> 
>>> I have adjusted SRA phase to split calls to DEFERRED_INIT per you suggestion.
>>> 
>>> And now the routine “bump_map” in 511.povray is like following:
>>> ...
>>> 
>>> # DEBUG BEGIN_STMT
>>> xcoor = 0.0;
>>> ycoor = 0.0;
>>> # DEBUG BEGIN_STMT
>>> index = .DEFERRED_INIT (index, 2);
>>> index2 = .DEFERRED_INIT (index2, 2);
>>> index3 = .DEFERRED_INIT (index3, 2);
>>> # DEBUG BEGIN_STMT
>>> colour1 = .DEFERRED_INIT (colour1, 2);
>>> colour2 = .DEFERRED_INIT (colour2, 2);
>>> colour3 = .DEFERRED_INIT (colour3, 2);
>>> # DEBUG BEGIN_STMT
>>> p1$0_181 = .DEFERRED_INIT (p1$0_195(D), 2);
>>> # DEBUG p1$0 => p1$0_181
>>> p1$1_184 = .DEFERRED_INIT (p1$1_182(D), 2);
>>> # DEBUG p1$1 => p1$1_184
>>> p1$2_172 = .DEFERRED_INIT (p1$2_185(D), 2);
>>> # DEBUG p1$2 => p1$2_172
>>> p2$0_177 = .DEFERRED_INIT (p2$0_173(D), 2);
>>> # DEBUG p2$0 => p2$0_177
>>> p2$1_135 = .DEFERRED_INIT (p2$1_178(D), 2);
>>> # DEBUG p2$1 => p2$1_135
>>> p2$2_137 = .DEFERRED_INIT (p2$2_136(D), 2);
>>> # DEBUG p2$2 => p2$2_137
>>> p3$0_377 = .DEFERRED_INIT (p3$0_376(D), 2);
>>> # DEBUG p3$0 => p3$0_377
>>> p3$1_379 = .DEFERRED_INIT (p3$1_378(D), 2);
>>> # DEBUG p3$1 => p3$1_379
>>> p3$2_381 = .DEFERRED_INIT (p3$2_380(D), 2);
>>> # DEBUG p3$2 => p3$2_381
>>> 
>>> 
>>> In the above, p1, p2, and p3 are all splitted to calls to DEFERRED_INIT of the components of p1, p2 and p3. 
>>> 
>>> With this change, the stack usage numbers with -fstack-usage for approach A, old approach D and new D with the splitting in SRA are:
>>> 
>>> Approach A	Approach D-old	Approach D-new
>>> 
>>> 	272			624			368
>>> 
>>> From the above, we can see that splitting the call to DEFERRED_INIT in SRA can reduce the stack usage increase dramatically. 
>>> 
>>> However, looks like that the stack size for D is still bigger than A. 
>>> 
>>> I checked the IR again, and found that the alias analysis might be responsible for this (by compare the image.cpp.026t.ealias for both A and D):
>>> 
>>> (Due to the call to:
>>> 
>>> colour1 = .DEFERRED_INIT (colour1, 2);
>>> )
>>> 
>>> ******Approach A:
>>> 
>>> Points_to analysis:
>>> 
>>> Constraints:
>>> …
>>> colour1 = &NULL
>>> …
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> ...
>>> callarg(53) = &colour1
>>> ...
>>> _53 = colour1
>>> 
>>> Points_to sets:
>>> …
>>> colour1 = { NULL ESCAPED NONLOCAL } same as _53
>>> ...
>>> CALLUSED(48) = { NULL ESCAPED NONLOCAL index colour1 }
>>> CALLCLOBBERED(49) = { NULL ESCAPED NONLOCAL index colour1 } same as CALLUSED(48)
>>> ...
>>> callarg(53) = { NULL ESCAPED NONLOCAL colour1 }
>>> 
>>> ******Apprach D:
>>> 
>>> Points_to analysis:
>>> 
>>> Constraints:
>>> …
>>> callarg(19) = colour1
>>> callarg(19) = &NONLOCAL
>>> colour1 = callarg(19) + UNKNOWN
>>> colour1 = &NONLOCAL
>>> …
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> colour1 = &NONLOCAL
>>> …
>>> callarg(74) = &colour1
>>> callarg(74) = callarg(74) + UNKNOWN
>>> callarg(74) = *callarg(74) + UNKNOWN
>>> …
>>> _53 = colour1
>>> _54 = _53
>>> _55 = _54 + UNKNOWN
>>> _55 = &NONLOCAL
>>> _56 = colour1
>>> _57 = _56
>>> _58 = _57 + UNKNOWN
>>> _58 = &NONLOCAL
>>> _59 = _55 + UNKNOWN
>>> _59 = _58 + UNKNOWN
>>> _60 = colour1
>>> _61 = _60
>>> _62 = _61 + UNKNOWN
>>> _62 = &NONLOCAL
>>> _63 = _59 + UNKNOWN
>>> _63 = _62 + UNKNOWN
>>> _64 = _63 + UNKNOWN
>>> ..
>>> Points_to set:
>>> …
>>> colour1 = { ESCAPED NONLOCAL } same as callarg(19)
>>> …
>>> CALLUSED(69) = { ESCAPED NONLOCAL index colour1 }
>>> CALLCLOBBERED(70) = { ESCAPED NONLOCAL index colour1 } same as CALLUSED(69)
>>> callarg(71) = { ESCAPED NONLOCAL }
>>> callarg(72) = { ESCAPED NONLOCAL }
>>> callarg(73) = { ESCAPED NONLOCAL }
>>> callarg(74) = { ESCAPED NONLOCAL colour1 }
>>> 
>>> My question:
>>> 
>>> Is it possible to adjust alias analysis to resolve this issue?
>> 
>> You probably want to handle .DEFERRED_INIT in tree-ssa-structalias.c
>> find_func_aliases_for_call (it's not a builtin but you can look in
>> the respective subroutine for examples).  Specifically you want to
>> avoid making anything escaped or clobbered.
> 
> Okay, thanks.
> 
> Will check on that.
> 
> Qing
>>> 
>> 
>> -- 
>> Richard Biener <rguenther@suse.de <mailto:rguenther@suse.de> <mailto:rguenther@suse.de <mailto:rguenther@suse.de>>>
>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)