[Bug tree-optimization/92341] missing -Warray-bounds indexing past the end of a compound literal

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92341

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2019-11-04
           Assignee|unassigned at gcc dot gnu.org      |msebor at gcc dot 
gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
The otherwise untested change below prevents SRA from folding the out-of-bounds
access and lets VRP diagnose the invalid access as follows:

pr82612.c:26:11: warning: array subscript 2 is outside array bounds of ‘int[2]’
[-Warray-bounds]
   26 |   return p[2];
      |          ~^~~
pr82612.c:25:19: note: while referencing ‘({anonymous})’
   25 |   int *p = (int[]){ 1, 2 };
      |                   ^


diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index 3f104238d93..63f1800f0d4 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -3068,6 +3068,13 @@ get_access_for_expr (tree expr)
       || !DECL_P (base))
     return NULL;

+  if (tree basesize = DECL_SIZE (base))
+    {
+      poly_int64 sz = tree_to_poly_int64 (basesize);
+      if (known_le (sz, offset))
+       return NULL;
+    }
+
   if (!bitmap_bit_p (candidate_bitmap, DECL_UID (base)))
     return NULL;