[Bug middle-end/92333] missing variable name referencing VLA in warnings

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92333

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2019-11-02
           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 changes the output to:

gcc -O2 -S -Wall pr92333.c
pr92333.c: In function ‘g’:
pr92333.c:9:3: warning: writing 20 bytes into a region of size 5
[-Wstringop-overflow=]
    9 |   __builtin_memcpy (vla, a, nelts * sizeof *a);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr92333.c:8:8: note: at offset 0 to object ‘vla.10’ with size 5 declared here
    8 |   char vla[nelts];
      |        ^~~
pr92333.c: In function ‘h’:
pr92333.c:18:3: warning: array subscript 2 is outside array bounds of ‘unsigned
char[5]’ [-Warray-bounds]
   18 |   __builtin_memcpy (vla, a, nelts * sizeof *a);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr92333.c:17:8: note: while referencing ‘vla.12’
   17 |   char vla[nelts];
      |        ^~~
pr92333.c:18:3: warning: array subscript 3 is outside array bounds of ‘unsigned
char[5]’ [-Warray-bounds]
   18 |   __builtin_memcpy (vla, a, nelts * sizeof *a);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr92333.c:17:8: note: while referencing ‘vla.12’
   17 |   char vla[nelts];
      |        ^~~
pr92333.c:18:3: warning: array subscript 4 is outside array bounds of ‘unsigned
char[5]’ [-Warray-bounds]
   18 |   __builtin_memcpy (vla, a, nelts * sizeof *a);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr92333.c:17:8: note: while referencing ‘vla.12’
   17 |   char vla[nelts];
      |        ^~~
pr92333.c:18:3: warning: writing 4 bytes into a region of size 1
[-Wstringop-overflow=]
   18 |   __builtin_memcpy (vla, a, nelts * sizeof *a);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr92333.c:17:8: note: at offset 0 to object ‘vla.12’ with size 5 declared here
   17 |   char vla[nelts];
      |        ^~~


diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index a8d0738fbb0..567aef8bc26 100644
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -2222,7 +2222,25 @@ fold_builtin_alloca_with_align (gimple *stmt)
   elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
   n_elem = size * 8 / BITS_PER_UNIT;
   array_type = build_array_type_nelts (elem_type, n_elem);
-  var = create_tmp_var (array_type);
+
+  if (tree ssa_name = SSA_NAME_IDENTIFIER (lhs))
+    {
+      /* Give the temporary a name derived from the name of the VLA
+        declaration so it can be referenced in diagnostics.  */
+      const char *name = IDENTIFIER_POINTER (ssa_name);
+      var = create_tmp_var (array_type, name);
+    }
+  else
+    var = create_tmp_var (array_type);
+
+  if (gimple *lhsdef = SSA_NAME_DEF_STMT (lhs))
+    {
+      /* Set the temporary's location to that of the VLA declaration
+        so it can be pointed to in diagnostics.  */
+      location_t loc = gimple_location (lhsdef);
+      DECL_SOURCE_LOCATION (var) = loc;
+    }
+
   SET_DECL_ALIGN (var, TREE_INT_CST_LOW (gimple_call_arg (stmt, 1)));
   if (uid != 0)
     SET_DECL_PT_UID (var, uid);