Re: [PATCH] Speed-up use-after-scope (re-writing to SSA) (version 2)

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Jan 09, 2017 at 03:58:04PM +0100, Martin Liška wrote:
> >> Well, having following sample:
> >>
> >> int
> >> main (int argc, char **argv)
> >> {
> >>   int *ptr = 0;
> >>
> >>   {
> >>     int a;
> >>     ptr = &a;
> >>     *ptr = 12345;
> >>   }
> >>
> >>   *ptr = 12345;
> >>   return *ptr;
> >> }
> >>

> I'm still not sure how to do that. Problem is that transformation from:
> 
>   ASAN_MARK (UNPOISON, &a, 4);
>   a = 5;
>   ASAN_MARK (POISON, &a, 4);
> 
> to 
> 
>   a_8 = 5;
>   a_9 = ASAN_POISON ();
> 
> happens in tree-ssa.c, after SSA is created, in situation where we prove the 'a'
> does not need to live in memory. Thus said, question is how to identify that we
> need to transform into SSA in a different way:
> 
>    a_10 = ASAN_POISON ();
>    ASAN_POISON (a_10);

I meant something like this (completely untested, and without the testcase
added to the testsuite).
The incremental patch as is relies on the ASAN_POISON_USE call having the
argument the result of ASAN_POISON, it would ICE if that is not the case
(especially if -fsanitize-recover=address).  Dunno if some optimization
might decide to create a PHI in between, say merge two unrelated vars for
if (something)
  {
    x_1 = ASAN_POISON ();
    ...
    ASAN_POISON_USE (x_1);
  }
else
  {
    y_2 = ASAN_POISON ();
    ...
    ASAN_POISON_USE (y_2);
  }
to turn that into:
if (something)
  x_1 = ASAN_POISON ();
else
  y_2 = ASAN_POISON ();
_3 = PHI <x_1, y_2>;
...
ASAN_POISON_USE (_3);

If it did, we would ICE because ASAN_POISON_USE would survive this way until
expansion.  A quick fix for the ICE (if it can ever happen) would be easy,
in sanopt remove ASAN_POISON_USE calls which have argument that is not lhs
of ASAN_POISON (all other ASAN_POISON_USE calls will be handled by my
incremental patch).  Of course that would also mean in that case we'd report
a read rather than write.  But if it can't happen or is very unlikely to
happen, then it is a non-issue.

Something missing from the patch is some change in DCE to remove ASAN_POISON
calls without lhs earlier.  I think we can't make ASAN_POISON ECF_CONST, we
don't want it to be merged for different variables.

--- gcc/internal-fn.def.jj	2017-01-16 13:19:49.000000000 +0100
+++ gcc/internal-fn.def	2017-01-16 14:25:37.427962196 +0100
@@ -167,6 +167,7 @@ DEF_INTERNAL_FN (ABNORMAL_DISPATCHER, EC
 DEF_INTERNAL_FN (ASAN_CHECK, ECF_TM_PURE | ECF_LEAF | ECF_NOTHROW, ".R...")
 DEF_INTERNAL_FN (ASAN_MARK, ECF_LEAF | ECF_NOTHROW, ".R..")
 DEF_INTERNAL_FN (ASAN_POISON, ECF_LEAF | ECF_NOTHROW | ECF_NOVOPS, NULL)
+DEF_INTERNAL_FN (ASAN_POISON_USE, ECF_LEAF | ECF_NOTHROW | ECF_NOVOPS, NULL)
 DEF_INTERNAL_FN (ADD_OVERFLOW, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 DEF_INTERNAL_FN (SUB_OVERFLOW, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 DEF_INTERNAL_FN (MUL_OVERFLOW, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
--- gcc/asan.c.jj	2017-01-16 13:19:49.000000000 +0100
+++ gcc/asan.c	2017-01-16 14:52:34.022044223 +0100
@@ -3094,6 +3094,8 @@ create_asan_shadow_var (tree var_decl,
     return *slot;
 }
 
+/* Expand ASAN_POISON ifn.  */
+
 bool
 asan_expand_poison_ifn (gimple_stmt_iterator *iter,
 			bool *need_commit_edge_insert,
@@ -3107,8 +3109,8 @@ asan_expand_poison_ifn (gimple_stmt_iter
       return true;
     }
 
-  tree shadow_var  = create_asan_shadow_var (SSA_NAME_VAR (poisoned_var),
-					     shadow_vars_mapping);
+  tree shadow_var = create_asan_shadow_var (SSA_NAME_VAR (poisoned_var),
+					    shadow_vars_mapping);
 
   bool recover_p;
   if (flag_sanitize & SANITIZE_USER_ADDRESS)
@@ -3122,16 +3124,16 @@ asan_expand_poison_ifn (gimple_stmt_iter
 						 ASAN_MARK_POISON),
 				  build_fold_addr_expr (shadow_var), size);
 
-  use_operand_p use_p;
+  gimple *use;
   imm_use_iterator imm_iter;
-  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, poisoned_var)
+  FOR_EACH_IMM_USE_STMT (use, imm_iter, poisoned_var)
     {
-      gimple *use = USE_STMT (use_p);
       if (is_gimple_debug (use))
 	continue;
 
       int nargs;
-      tree fun = report_error_func (false, recover_p, tree_to_uhwi (size),
+      bool store_p = gimple_call_internal_p (use, IFN_ASAN_POISON_USE);
+      tree fun = report_error_func (store_p, recover_p, tree_to_uhwi (size),
 				    &nargs);
 
       gcall *call = gimple_build_call (fun, 1,
@@ -3160,7 +3162,10 @@ asan_expand_poison_ifn (gimple_stmt_iter
       else
 	{
 	  gimple_stmt_iterator gsi = gsi_for_stmt (use);
-	  gsi_insert_before (&gsi, call, GSI_NEW_STMT);
+	  if (store_p)
+	    gsi_replace (&gsi, call, true);
+	  else
+	    gsi_insert_before (&gsi, call, GSI_NEW_STMT);
 	}
     }
 
--- gcc/tree-into-ssa.c.jj	2017-01-01 12:45:35.000000000 +0100
+++ gcc/tree-into-ssa.c	2017-01-16 14:32:14.853808726 +0100
@@ -38,6 +38,7 @@ along with GCC; see the file COPYING3.
 #include "tree-ssa.h"
 #include "domwalk.h"
 #include "statistics.h"
+#include "asan.h"
 
 #define PERCENT(x,y) ((float)(x) * 100.0 / (float)(y))
 
@@ -1807,6 +1808,26 @@ maybe_replace_use_in_debug_stmt (use_ope
 }
 
 
+/* If DEF has x_5 = ASAN_POISON () as its current def, add
+   ASAN_POISON_USE (x_5) stmt before GSI to denote the stmt writes into
+   a poisoned (out of scope) variable.  */
+
+static void
+maybe_add_asan_poison_write (tree def, gimple_stmt_iterator *gsi)
+{
+  tree cdef = get_current_def (def);
+  if (cdef != NULL
+      && TREE_CODE (cdef) == SSA_NAME
+      && gimple_call_internal_p (SSA_NAME_DEF_STMT (cdef), IFN_ASAN_POISON))
+    {
+      gcall *call
+	= gimple_build_call_internal (IFN_ASAN_POISON_USE, 1, cdef);
+      gimple_set_location (call, gimple_location (gsi_stmt (*gsi)));
+      gsi_insert_before (gsi, call, GSI_SAME_STMT);
+    }
+}
+
+
 /* If the operand pointed to by DEF_P is an SSA name in NEW_SSA_NAMES
    or OLD_SSA_NAMES, or if it is a symbol marked for renaming,
    register it as the current definition for the names replaced by
@@ -1837,7 +1858,11 @@ maybe_register_def (def_operand_p def_p,
 	      def = get_or_create_ssa_default_def (cfun, sym);
 	    }
 	  else
-	    def = make_ssa_name (def, stmt);
+	    {
+	      if (asan_sanitize_use_after_scope ())
+		maybe_add_asan_poison_write (def, &gsi);
+	      def = make_ssa_name (def, stmt);
+	    }
 	  SET_DEF (def_p, def);
 
 	  tree tracked_var = target_for_debug_bind (sym);
--- gcc/internal-fn.c.jj	2017-01-16 13:19:49.000000000 +0100
+++ gcc/internal-fn.c	2017-01-16 14:26:10.828529039 +0100
@@ -388,6 +388,14 @@ expand_ASAN_POISON (internal_fn, gcall *
   gcc_unreachable ();
 }
 
+/* This should get expanded in the sanopt pass.  */
+
+static void
+expand_ASAN_POISON_USE (internal_fn, gcall *)
+{
+  gcc_unreachable ();
+}
+
 /* This should get expanded in the tsan pass.  */
 
 static void


	Jakub