Bootstrapped and regtested on x86_64-pc-linux-gnu, does this
look OK for trunk and perhaps 14?
-- >8 --
Our constraint recursion diagnostics are not ideal because they
usually show the atom with an uninstantiated parameter mapping, e.g
concepts-recursive-sat5.C:6:41: error: satisfaction of atomic constraint
‘requires(A a, T t) {a | t;} [with T = T]’ depends on itself
This is a consequence of our two-level caching of atomic constraints,
where we first cache the uninstantiated atom+args and then the
instantiated atom+no args, and most likely the first level of caching
detects the recursion, at which point we have no way to get a hold of
the instantiated atom.
This patch fixes this by linking the the first level of caching to the
second level, so that we can conveniently print the instantiated atom in
case of constraint recursion detected from the first level of caching.
Alternatively we could make only the second level of caching diagnose
constraint recursion but then we'd no longer catch constraint recursion
that occurs during parameter mapping instantiation. This current approach
seems simpler, and it also seems natural to have the two levels of caching
linked in some way anyway.
gcc/cp/ChangeLog:
* constraint.cc (struct sat_entry): New data member inst_entry.
(satisfaction_cache::get): Use it to prefer printing the
instantiated atom in case of constraint recursion.
(satisfy_atom): Set inst_entry on the first entry to point to
the second entry.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-recursive-sat2.C: Verify that the
instantiated parameter mapping is printed.
* g++.dg/cpp2a/concepts-recursive-sat5.C: Likewise.
---
gcc/cp/constraint.cc | 12 ++++++++++--
gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat2.C | 3 ++-
gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat5.C | 3 ++-
3 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 44fb086c6306..1bb237f5bb4f 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1895,6 +1895,10 @@ struct GTY((for_user)) sat_entry
the first time. */
tree result;
+ /* For a !ATOMIC_CONSTR_MAP_INSTANTIATED_P atom, this is the entry
+ for the corresponding atom after instantiating its mapping. */
+ sat_entry *inst_entry;
+
/* The value of input_location when satisfaction of ATOM+ARGS was first
performed. */
location_t location;
@@ -2093,10 +2097,12 @@ satisfaction_cache::get ()
{
/* If we get here, it means satisfaction is self-recursive. */
gcc_checking_assert (!entry->result || seen_error ());
+ /* Prefer printing the instantiated mapping. */
+ tree atom = entry->inst_entry ? entry->inst_entry->atom : entry->atom;
if (info.noisy ())
- error_at (EXPR_LOCATION (ATOMIC_CONSTR_EXPR (entry->atom)),
+ error_at (EXPR_LOCATION (ATOMIC_CONSTR_EXPR (atom)),
"satisfaction of atomic constraint %qE depends on itself",
- entry->atom);
+ atom);
return error_mark_node;
}
@@ -2416,6 +2422,8 @@ satisfy_atom (tree t, tree args, sat_info info)
gcc_assert (!ATOMIC_CONSTR_MAP_INSTANTIATED_P (t));
ATOMIC_CONSTR_MAP_INSTANTIATED_P (t) = true;
satisfaction_cache inst_cache (t, /*args=*/NULL_TREE, info);
+ if (cache.entry)
+ cache.entry->inst_entry = inst_cache.entry;
if (tree r = inst_cache.get ())
{
cache.entry->location = inst_cache.entry->location;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat2.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat2.C
index 9bc96f58979d..a264f26bc55d 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat2.C
@@ -1,7 +1,8 @@
// { dg-do compile { target c++20 } }
template<typename T>
-concept Fooable = requires(T t) { foo(t); }; // { dg-error "depends on itself"
}
+concept Fooable = requires(T t) { foo(t); };
+// { dg-error "T = test::S]' depends on itself" "" { target *-*-* } .-1 }
template<Fooable T>
void foo(T t) { }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat5.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat5.C
index ba564873a204..63e032494e3d 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat5.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat5.C
@@ -3,7 +3,8 @@
struct A { };
-template<typename T> concept pipeable = requires(A a, T t) { a | t; }; // {
dg-error "depends on itself" }
+template<typename T> concept pipeable = requires(A a, T t) { a | t; };
+// { dg-error "with T = int]' depends on itself" "" { target *-*-* } .-1 }
template<pipeable T> void operator|(A, T);
--
2.49.0.221.g485f5f8636
