[PATCH] Add UBSAN_{PTR,BOUNDS} folding (PR sanitizer/81981, take 2)

[Jakub Jelinek]

On Fri, Sep 01, 2017 at 07:10:51PM +0200, Richard Biener wrote:
> OK, I thought we have one.  Can you add a helper for it please? 
> replace_with_nop or so?  I thought there's maybe replace_with_value which
> handles null lhs by replacing with nop.  (can't check, writing from phone)

Actually, you're right, replace_call_with_value does the right thing
when called on call without lhs (all these internal fns don't have lhs),
and NULL_TREE val ensures we'd ICE if that ever wasn't the case.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2017-09-01  Jakub Jelinek  <ja...@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.  Use replace_call_with_value with NULL instead of
        gsi_replace, unlink_stmt_vdef and release_defs.

        * gcc.dg/ubsan/pr81981.c: New test.

--- gcc/gimple-fold.c.jj        2017-09-01 09:26:37.054748039 +0200
+++ gcc/gimple-fold.c   2017-09-01 19:37:03.283795450 +0200
@@ -3936,18 +3936,43 @@ 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)))
+             {
+               replace_call_with_value (gsi, NULL_TREE);
+               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);
-             release_defs (stmt);
+             replace_call_with_value (gsi, NULL_TREE);
              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))
+                 {
+                   replace_call_with_value (gsi, NULL_TREE);
+                   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     2017-09-01 19:35:37.555782465 
+0200
+++ gcc/testsuite/gcc.dg/ubsan/pr81981.c        2017-09-01 19:35:37.555782465 
+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