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 306ebf2c71f74bacf8d821de51b5a115a8e1a5f7..a4fac1932785cee3d972a987e839f0f709166964 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-25  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.
+
 2020-05-24  Iain Sandoe  <iain@sandoe.co.uk>
 
        Backported from mainline

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index b8f03d185411cdad40efabd1e5a794c16df4d83f..e025dd7a38878af364a4e335229a6d542ae38eeb 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)