On 3/24/22 10:32, Patrick Palka wrote:
Here we weren't respecting SFINAE when evaluating a substituted call to
a consteval function, which caused us to reject the new testcase below.
This patch fixes this by making build_over_call use the SFINAE-friendly
version of cxx_constant_value.
This change causes us to no longer diagnose ahead of time a couple of
invalid non-dependent consteval calls in consteval-if2.C (with
-fchecking=2). These errors were apparently coming from the call to
fold_non_dependent_expr in build_non_dependent_expr (for the RHS of the +=)
despite complain=tf_none being passed. Now that build_over_call
respects the value of complain during constant evaluation of a consteval
call, the errors are gone.
That the errors don't occur without -fchecking=2 is a regression caused
by r12-7264-gc19f317a78c0e4 and is the subject of PR104620. As described
in comment #5, I think it was only an accident that we were diagnosing
these two calls correctly before r12-7264, so perhaps we can live
without them in GCC 12. To that end this patch just XFAILs the two tests.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
OK.
PR c++/104620
gcc/cp/ChangeLog:
* call.cc (build_over_call): Use cxx_constant_value_sfinae
instead of cxx_constant_value to evaluate a consteval call.
* constexpr.cc (cxx_constant_value_sfinae): Add decl parameter
and pass it to cxx_eval_outermost_constant_expr.
* cp-tree.h (cxx_constant_value_sfinae): Add decl parameter.
* pt.cc (fold_targs_r): Pass NULL_TREE as decl to
cxx_constant_value_sfinae.
gcc/testsuite/ChangeLog:
* g++.dg/cpp23/consteval-if2.C: XFAIL two dg-error tests where
the argument to the non-dependent consteval call is wrapped in
NON_DEPENDENT_EXPR.
* g++.dg/cpp2a/consteval30.C: New test.
---
gcc/cp/call.cc | 2 +-
gcc/cp/constexpr.cc | 4 ++--
gcc/cp/cp-tree.h | 2 +-
gcc/cp/pt.cc | 2 +-
gcc/testsuite/g++.dg/cpp23/consteval-if2.C | 4 ++--
gcc/testsuite/g++.dg/cpp2a/consteval30.C | 12 ++++++++++++
6 files changed, 19 insertions(+), 7 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/consteval30.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 23d3fc496b8..ec6c5d5baa2 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -9939,7 +9939,7 @@ build_over_call (struct z_candidate *cand, int flags,
tsubst_flags_t complain)
obj_arg = TREE_OPERAND (addr, 0);
}
}
- call = cxx_constant_value (call, obj_arg);
+ call = cxx_constant_value_sfinae (call, obj_arg, complain);
if (obj_arg && !error_operand_p (call))
call = build2 (INIT_EXPR, void_type_node, obj_arg, call);
call = convert_from_reference (call);
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index a3136ce819d..2163a328e74 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -7959,10 +7959,10 @@ cxx_constant_value (tree t, tree decl)
/* As above, but respect SFINAE. */
tree
-cxx_constant_value_sfinae (tree t, tsubst_flags_t complain)
+cxx_constant_value_sfinae (tree t, tree decl, tsubst_flags_t complain)
{
bool sfinae = !(complain & tf_error);
- tree r = cxx_eval_outermost_constant_expr (t, sfinae, true, true);
+ tree r = cxx_eval_outermost_constant_expr (t, sfinae, true, true, false,
decl);
if (sfinae && !TREE_CONSTANT (r))
r = error_mark_node;
return r;
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 1bd7bc6fca2..2f718852ac1 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -8414,7 +8414,7 @@ extern bool require_constant_expression (tree);
extern bool require_rvalue_constant_expression (tree);
extern bool require_potential_rvalue_constant_expression (tree);
extern tree cxx_constant_value (tree, tree =
NULL_TREE);
-extern tree cxx_constant_value_sfinae (tree, tsubst_flags_t);
+extern tree cxx_constant_value_sfinae (tree, tree, tsubst_flags_t);
extern void cxx_constant_dtor (tree, tree);
extern tree cxx_constant_init (tree, tree = NULL_TREE);
extern tree maybe_constant_value (tree, tree = NULL_TREE, bool =
false);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 715eea27577..173bc3a8c7f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -19811,7 +19811,7 @@ fold_targs_r (tree targs, tsubst_flags_t complain)
&& !glvalue_p (elt)
&& !TREE_CONSTANT (elt))
{
- elt = cxx_constant_value_sfinae (elt, complain);
+ elt = cxx_constant_value_sfinae (elt, NULL_TREE, complain);
if (elt == error_mark_node)
return false;
}
diff --git a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
index f7053b91c3c..d1845da9e58 100644
--- a/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
+++ b/gcc/testsuite/g++.dg/cpp23/consteval-if2.C
@@ -77,11 +77,11 @@ qux (int x)
}
else
{
- r += foo (8 * x); // { dg-error "is not a constant expression" }
+ r += foo (8 * x); // { dg-error "is not a constant expression" ""
{ xfail *-*-* } }
}
if ! consteval // { dg-warning "'if consteval' only available with" ""
{ target c++20_only } }
{
- r += foo (32 * x);// { dg-error "is not a constant expression" }
+ r += foo (32 * x);// { dg-error "is not a constant expression" "" {
xfail *-*-* } }
}
if consteval // { dg-warning "'if consteval' only available with"
"" { target c++20_only } }
{
diff --git a/gcc/testsuite/g++.dg/cpp2a/consteval30.C
b/gcc/testsuite/g++.dg/cpp2a/consteval30.C
new file mode 100644
index 00000000000..d393dcc0857
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/consteval30.C
@@ -0,0 +1,12 @@
+// Test SFINAE behavior for an invalid consteval call.
+// { dg-do compile { target c++20 } }
+
+consteval int deref(const int* x) { return *x; }
+
+template<const int* P, int = deref(P)> // { dg-bogus "null pointer" }
+constexpr int f(int) { return 0; }
+
+template<const int* P>
+constexpr int f(...) { return 1; }
+
+static_assert(f<nullptr>(0) == 1);
