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 --git a/gcc/vec.h b/gcc/vec.h
index 9604edb1c3cf3680a264e1bf1c67e83b0b2decf4..0ea7a49573400f4f767f3aa9443d9306745dc7e1 100644 (file)
--- 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;
   }