[PATCH] Add UBSAN_{PTR,BOUNDS} folding (PR sanitizer/81981)

[Jakub Jelinek]

On Fri, Sep 01, 2017 at 02:32:43PM +0200, Richard Biener wrote:
> On September 1, 2017 1:16:54 PM GMT+02:00, Jakub Jelinek <jakub@redhat.com> wrote:
> >Hi!
> >
> >This patch fixes the following testcase by folding some ubsan internal
> >fns
> >we'd either remove anyway during sanopt, or lower into if (cond)
> >do_something during sanopt where cond would be always false.
> >
> >Additionally, I've tried to clean up a little bit IFN_UBSAN_OBJECT_SIZE
> >handling by using variables for the call arguments that make it clear
> >what the arguments are.
> >
> >Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> 
> I think there's a helper for replace - with-nop. 

Can't find it.
gimplify_and_update_call_from_tree has to add it, but I'd need
to call it with something that gimplifies into empty sequence (void_node?)
and it would still go through push_gimplify_context/gimplify_and_add/pop_gimplify_context
etc., which looks quite expensive.

> >2017-09-01  Jakub Jelinek  <jakub@redhat.com>
> >
> >	PR sanitizer/81981
> >	* gimple-fold.c (gimple_fold_call): Optimize away useless UBSAN_PTR
> >	and UBSAN_BOUNDS internal calls.  Clean up IFN_UBSAN_OBJECT_SIZE
> >	handling.
> >
> >	* gcc.dg/ubsan/pr81981.c: New test.
> >
> >--- gcc/gimple-fold.c.jj	2017-08-10 02:31:21.000000000 +0200
> >+++ gcc/gimple-fold.c	2017-08-29 18:50:49.993673432 +0200
> >@@ -3938,11 +3938,23 @@ gimple_fold_call (gimple_stmt_iterator *
> > 					gimple_call_arg (stmt, 2));
> > 	  break;
> > 	case IFN_UBSAN_OBJECT_SIZE:
> >-	  if (integer_all_onesp (gimple_call_arg (stmt, 2))
> >-	      || (TREE_CODE (gimple_call_arg (stmt, 1)) == INTEGER_CST
> >-		  && TREE_CODE (gimple_call_arg (stmt, 2)) == INTEGER_CST
> >-		  && tree_int_cst_le (gimple_call_arg (stmt, 1),
> >-				      gimple_call_arg (stmt, 2))))
> >+	  {
> >+	    tree offset = gimple_call_arg (stmt, 1);
> >+	    tree objsize = gimple_call_arg (stmt, 2);
> >+	    if (integer_all_onesp (objsize)
> >+		|| (TREE_CODE (offset) == INTEGER_CST
> >+		    && TREE_CODE (objsize) == INTEGER_CST
> >+		    && tree_int_cst_le (offset, objsize)))
> >+	      {
> >+		gsi_replace (gsi, gimple_build_nop (), false);
> >+		unlink_stmt_vdef (stmt);
> >+		release_defs (stmt);
> >+		return true;
> >+	      }
> >+	  }
> >+	  break;
> >+	case IFN_UBSAN_PTR:
> >+	  if (integer_zerop (gimple_call_arg (stmt, 1)))
> > 	    {
> > 	      gsi_replace (gsi, gimple_build_nop (), false);
> > 	      unlink_stmt_vdef (stmt);
> >@@ -3950,6 +3962,25 @@ gimple_fold_call (gimple_stmt_iterator *
> > 	      return true;
> > 	    }
> > 	  break;
> >+	case IFN_UBSAN_BOUNDS:
> >+	  {
> >+	    tree index = gimple_call_arg (stmt, 1);
> >+	    tree bound = gimple_call_arg (stmt, 2);
> >+	    if (TREE_CODE (index) == INTEGER_CST
> >+		&& TREE_CODE (bound) == INTEGER_CST)
> >+	      {
> >+		index = fold_convert (TREE_TYPE (bound), index);
> >+		if (TREE_CODE (index) == INTEGER_CST
> >+		    && tree_int_cst_le (index, bound))
> >+		  {
> >+		    gsi_replace (gsi, gimple_build_nop (), false);
> >+		    unlink_stmt_vdef (stmt);
> >+		    release_defs (stmt);
> >+		    return true;
> >+		  }
> >+	      }
> >+	  }
> >+	  break;
> > 	case IFN_GOACC_DIM_SIZE:
> > 	case IFN_GOACC_DIM_POS:
> > 	  result = fold_internal_goacc_dim (stmt);
> >--- gcc/testsuite/gcc.dg/ubsan/pr81981.c.jj	2017-08-29
> >18:54:33.826107761 +0200
> >+++ gcc/testsuite/gcc.dg/ubsan/pr81981.c	2017-08-29 18:55:36.721386827
> >+0200
> >@@ -0,0 +1,21 @@
> >+/* PR sanitizer/81981 */
> >+/* { dg-do compile } */
> >+/* { dg-options "-O2 -Wmaybe-uninitialized -fsanitize=undefined
> >-ffat-lto-objects" } */
> >+
> >+int v;
> >+
> >+int
> >+foo (int i)
> >+{
> >+  int t[1], u[1];
> >+  int n = 0;
> >+
> >+  if (i)
> >+    {
> >+      t[n] = i;
> >+      u[0] = i;
> >+    }
> >+
> >+  v = u[0];		/* { dg-warning "may be used uninitialized in this
> >function" } */
> >+  return t[0];		/* { dg-warning "may be used uninitialized in this
> >function" } */
> >+}
> >
> >	Jakub

	Jakub