[gcc r16-2600] Fix UB in string_slice::operator== (PR 121261)

[Alfie Richards via Gcc-cvs]

https://gcc.gnu.org/g:c1102be3b25bde9989561b2610f8ee721a33a8e7

commit r16-2600-gc1102be3b25bde9989561b2610f8ee721a33a8e7
Author: Alfie Richards <alfie.richa...@arm.com>
Date:   Mon Jul 28 13:32:45 2025 +0000

    Fix UB in string_slice::operator== (PR 121261)
    
    This adds a nullptr check to fix a regression where it is possible to call
    `memcmp (NULL, NULL, 0)` which is UB prior to C26.
    
    This fixes the bootstrap-ubsan build.
    
    gcc/ChangeLog:
            PR middle-end/121261
            * vec.h: Add null ptr check.

Diff:
---
 gcc/vec.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/gcc/vec.h b/gcc/vec.h
index 9604edb1c3cf..0ea7a4957340 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -2514,6 +2514,10 @@ public:
       return false;
     if (lhs.size () != rhs.size ())
       return false;
+    /* Case where either is a NULL pointer and therefore, as both are valid,
+       both are empty slices with length 0.  */
+    if (lhs.size () == 0)
+      return true;
     return memcmp (lhs.begin (), rhs.begin (), lhs.size ()) == 0;
   }