Re: [PATCH] tree-object-size: Always set computed bit for bdos [PR113012]

[Siddhesh Poyarekar]

On 2023-12-19 17:57, Jakub Jelinek wrote:
On Mon, Dec 18, 2023 at 11:42:52AM -0500, Siddhesh Poyarekar wrote:
It is always safe to set the computed bit for dynamic object sizes at
the end of collect_object_sizes_for because even in case of a dependency
loop encountered in nested calls, we have an SSA temporary to actually
finish the object size expression.  The reexamine pass for dynamic
object sizes is only for propagation of unknowns and gimplification of
the size expressions, not for loop resolution as in the case of static
object sizes.
gcc/ChangeLog:

        PR tree-optimization/113012
        * gcc.dg/ubsan/pr113012.c: New test case.

gcc/testsuite/ChangeLog:

        PR tree-optimization/113012
        * tree-object-size.cc (compute_builtin_object_size): Expand
        comment for dynamic object sizes.
        (collect_object_sizes_for): Always set COMPUTED bitmap for
        dynamic object sizes.

You have the gcc/ChangeLog and gcc/testsuite/ChangeLog hunks swapped,
I think this wouldn't get through pre-commit hook.

Oops, fixed.

--- a/gcc/tree-object-size.cc
+++ b/gcc/tree-object-size.cc
@@ -1185,10 +1185,12 @@ compute_builtin_object_size (tree ptr, int 
object_size_type,
          osi.tos = NULL;
        }
  
-      /* First pass: walk UD chains, compute object sizes that
-        can be computed.  osi.reexamine bitmap at the end will
-        contain what variables were found in dependency cycles
-        and therefore need to be reexamined.  */
+      /* First pass: walk UD chains, compute object sizes that can be computed.
+        osi.reexamine bitmap at the end will contain what variables that need

This wording is weird.
Perhaps ... will contain versions of SSA_NAMEs that need
to be reexamined. ?
Because varno seems to be SSA_NAME_VERSION.

Ack, it's unrelated to my change, but fixed since I touched the comment 
block.

@@ -1823,11 +1825,16 @@ collect_object_sizes_for (struct object_size_info *osi, 
tree var)
        gcc_unreachable ();
      }
  
-  if (! reexamine || object_sizes_unknown_p (object_size_type, varno))
+  /* Dynamic sizes use placeholder temps to return an answer, so it is always
+   * safe to set COMPUTED for them.  */

We don't use this style of comments, please replace the * at the start of
second line with a space.

Oops, fixed.

+  if ((object_size_type & OST_DYNAMIC)
+      || !reexamine || object_sizes_unknown_p (object_size_type, varno))
      {
        bitmap_set_bit (computed[object_size_type], varno);
        if (!(object_size_type & OST_DYNAMIC))
        bitmap_clear_bit (osi->reexamine, varno);
+      else if (reexamine)
+       bitmap_set_bit (osi->reexamine, varno);
      }
    else
      {

Otherwise LGTM, but please wait at least a few weeks before backporting to
13.

OK, I'll push with fixes to trunk in a bit and then push to 13 next year.

Thanks,
Sid