c++: generic lambda and -fsanitize=vla-bound [PR93822]

Within the generic lambda the VLA capture proxy VAR_DECL has DECL_VALUE_EXPR
which is a NOP_EXPR to the VLA type of the proxy.  The problem here was that
when instantiating we were tsubsting that type twice, once for the type of
the DECL and once for the type of the NOP_EXPR, and getting two
different (though equivalent) types.  Then gimplify_type_sizes fixed up the
type of the DECL, but that didn't affect the type of the NOP_EXPR, leading
to sadness.

Fixed by directly reusing the type from the DECL.

gcc/cp/ChangeLog
2020-05-01  Jason Merrill  <jason@redhat.com>

	PR c++/93822
	* pt.c (tsubst_decl): Make sure DECL_VALUE_EXPR continues to have
	the same type as the variable.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 3c57945cecfd84641dcb8f7ec26cb035b057a072..039e946f9507268d26d38ba232e9fcec489c5140 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-01  Jason Merrill  <jason@redhat.com>
+
+       PR c++/93822
+       * pt.c (tsubst_decl): Make sure DECL_VALUE_EXPR continues to have
+       the same type as the variable.
+
 2020-04-30  Jason Merrill  <jason@redhat.com>
            Nathan Sidwell  <nathan@acm.org>
 

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index d28585efd17a73a4882bebb7dc3535c1ea00e962..9332865cf468749689c95f1977bdbf40f5a30d37 100644 (file)
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14609,6 +14609,11 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
            if (DECL_HAS_VALUE_EXPR_P (t))
              {
                tree ve = DECL_VALUE_EXPR (t);
+               /* If the DECL_VALUE_EXPR is converted to the declared type,
+                  preserve the identity so that gimplify_type_sizes works.  */
+               bool nop = (TREE_CODE (ve) == NOP_EXPR);
+               if (nop)
+                 ve = TREE_OPERAND (ve, 0);
                ve = tsubst_expr (ve, args, complain, in_decl,
                                  /*constant_expression_p=*/false);
                if (REFERENCE_REF_P (ve))
@@ -14616,6 +14621,10 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
                    gcc_assert (TYPE_REF_P (type));
                    ve = TREE_OPERAND (ve, 0);
                  }
+               if (nop)
+                 ve = build_nop (type, ve);
+               else
+                 gcc_checking_assert (TREE_TYPE (ve) == type);
                SET_DECL_VALUE_EXPR (r, ve);
              }
            if (CP_DECL_THREAD_LOCAL_P (r)