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

[Siddhesh Poyarekar]

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.

Signed-off-by: Siddhesh Poyarekar <siddh...@gotplt.org>
---
Testing:

- Bootstrapped x86_64 and config=ubsan
- Tested i686

OK for trunk and backport to gcc 13 branch?

 gcc/testsuite/gcc.dg/ubsan/pr113012.c | 17 +++++++++++++++++
 gcc/tree-object-size.cc               | 17 ++++++++++++-----
 2 files changed, 29 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/ubsan/pr113012.c

diff --git a/gcc/testsuite/gcc.dg/ubsan/pr113012.c 
b/gcc/testsuite/gcc.dg/ubsan/pr113012.c
new file mode 100644
index 00000000000..4fc38cd1171
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ubsan/pr113012.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=undefined" } */
+
+int *
+foo (int x, int y, int z, int w)
+{
+  int *p = __builtin_malloc (z * sizeof (int));
+  int *q = p - 1;
+  while (--x > 0)
+    {
+      if (w + 1 > y)
+       q = p - 1;
+      ++*q;
+      ++q;
+    }
+  return p;
+}
diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
index 28f27adf9ca..434b2fc0bf5 100644
--- 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
+        to be reexamined.  For both static and dynamic size computation,
+        reexamination is for propagation across dependency loops. The dynamic
+        case has the additional use case where the computed expression needs
+        to be gimplified.  */
       osi.pass = 0;
       osi.changed = false;
       collect_object_sizes_for (&osi, ptr);
@@ -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.  */
+  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
     {
-- 
2.43.0