On Thu, Oct 20, 2022 at 10:51:14AM -0400, Jason Merrill wrote:
> That seems like a bug; for VECTOR_TYPE we should fold even if !changed.
>
> > Also, the reason for the short-cutting is I think trying to avoid
> > allocating a new CONSTRUCTOR when nothing changes and we just create
> > GC garbage by it.
>
> We might limit the shortcut to non-vector types by hoisting the vector check
> in reduced_constant_expression_p out of the CONSTRUCTOR_NO_CLEARING
> condition:
>
> > if (CONSTRUCTOR_NO_CLEARING (t))
> > {
> > if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
> > /* An initialized vector would have a VECTOR_CST. */
> > return false;
>
> then we could remove the fold in the shortcut.
Ok, so like this?
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2022-10-21 Jakub Jelinek <ja...@redhat.com>
PR c++/107295
* constexpr.cc (reduced_constant_expression_p) <case CONSTRUCTOR>:
Return false for VECTOR_TYPE CONSTRUCTORs even without
CONSTRUCTOR_NO_CLEARING set on them.
(cxx_eval_bare_aggregate): If constant but !changed, fold before
returning VECTOR_TYPE_P CONSTRUCTOR.
(cxx_eval_constant_expression) <case CONSTRUCTOR>: Don't fold
TREE_CONSTANT CONSTRUCTOR, just return it.
* g++.dg/ext/vector42.C: New test.
--- gcc/cp/constexpr.cc.jj 2022-10-19 11:20:28.960225787 +0200
+++ gcc/cp/constexpr.cc 2022-10-20 18:43:42.952440364 +0200
@@ -3104,12 +3104,12 @@ reduced_constant_expression_p (tree t)
case CONSTRUCTOR:
/* And we need to handle PTRMEM_CST wrapped in a CONSTRUCTOR. */
tree field;
+ if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
+ /* An initialized vector would have a VECTOR_CST. */
+ return false;
if (CONSTRUCTOR_NO_CLEARING (t))
{
- if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
- /* An initialized vector would have a VECTOR_CST. */
- return false;
- else if (TREE_CODE (TREE_TYPE (t)) == ARRAY_TYPE)
+ if (TREE_CODE (TREE_TYPE (t)) == ARRAY_TYPE)
{
/* There must be a valid constant initializer at every array
index. */
@@ -4956,8 +4956,14 @@ cxx_eval_bare_aggregate (const constexpr
TREE_SIDE_EFFECTS (ctx->ctor) = side_effects_p;
}
}
- if (*non_constant_p || !changed)
+ if (*non_constant_p)
return t;
+ if (!changed)
+ {
+ if (VECTOR_TYPE_P (type))
+ t = fold (t);
+ return t;
+ }
t = ctx->ctor;
if (!t)
t = build_constructor (type, NULL);
@@ -7387,11 +7393,10 @@ cxx_eval_constant_expression (const cons
case CONSTRUCTOR:
if (TREE_CONSTANT (t) && reduced_constant_expression_p (t))
{
- /* Don't re-process a constant CONSTRUCTOR, but do fold it to
- VECTOR_CST if applicable. */
+ /* Don't re-process a constant CONSTRUCTOR. */
verify_constructor_flags (t);
if (TREE_CONSTANT (t))
- return fold (t);
+ return t;
}
r = cxx_eval_bare_aggregate (ctx, t, lval,
non_constant_p, overflow_p);
--- gcc/testsuite/g++.dg/ext/vector42.C.jj 2022-10-20 17:57:42.767848544
+0200
+++ gcc/testsuite/g++.dg/ext/vector42.C 2022-10-20 17:57:42.767848544 +0200
@@ -0,0 +1,12 @@
+// PR c++/107295
+// { dg-do compile { target c++11 } }
+
+template <typename T> struct A {
+ typedef T __attribute__((vector_size (sizeof (int)))) V;
+};
+template <int, typename T> using B = typename A<T>::V;
+template <typename T> using V = B<4, T>;
+using F = V<float>;
+constexpr F a = F () + 0.0f;
+constexpr F b = F () + (float) 0.0;
+constexpr F c = F () + (float) 0.0L;
Jakub
