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* [gcc r12-7102] c++: lambda in pack expansion using pack in constraint [PR103706]
@ 2022-02-08 13:48 Patrick Palka
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From: Patrick Palka @ 2022-02-08 13:48 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:db5f1c17031ad8a898d77121f1e0e0141306e22a
commit r12-7102-gdb5f1c17031ad8a898d77121f1e0e0141306e22a
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Feb 8 08:46:32 2022 -0500
c++: lambda in pack expansion using pack in constraint [PR103706]
Here when expanding the pack expansion pattern containing a constrained
lambda, the template argument for each Ts is an ARGUMENT_PACK_SELECT,
which we store inside the lambda's LAMBDA_EXPR_REGEN_INFO. Then during
satisfaction of the lambda's constraint C<Ts> the satisfaction cache
uses this argument as part of the key to the corresponding sat_entry, but
iterative_hash_template_arg and template_args_equal deliberately don't
handle ARGUMENT_PACK_SELECT.
Since it's wrong to preserve ARGUMENT_PACK_SELECT inside a hash table
due to its instability (as documented in iterative_hash_template_arg),
this patch helps make sure the satisfaction cache doesn't see such trees
by resolving ARGUMENT_PACK_SELECT arguments before adding them to
LAMBDA_EXPR_REGEN_INFO.
PR c++/103706
gcc/cp/ChangeLog:
* pt.cc (preserve_args): New function.
(tsubst_lambda_expr): Use it when setting LAMBDA_EXPR_REGEN_INFO.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-lambda19.C: New test.
Diff:
---
gcc/cp/pt.cc | 40 ++++++++++++++++++++++++--
gcc/testsuite/g++.dg/cpp2a/concepts-lambda19.C | 11 +++++++
2 files changed, 49 insertions(+), 2 deletions(-)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index b58067d50e9..5115fba8d0f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3743,6 +3743,41 @@ argument_pack_select_arg (tree t)
return arg;
}
+/* Return a modification of ARGS that's suitable for preserving inside a hash
+ table. In particular, this replaces each ARGUMENT_PACK_SELECT with its
+ underlying argument. ARGS is copied (upon modification) iff COW_P. */
+
+static tree
+preserve_args (tree args, bool cow_p = true)
+{
+ if (!args)
+ return NULL_TREE;
+
+ for (int i = 0, len = TREE_VEC_LENGTH (args); i < len; ++i)
+ {
+ tree t = TREE_VEC_ELT (args, i);
+ tree r;
+ if (!t)
+ r = NULL_TREE;
+ else if (TREE_CODE (t) == ARGUMENT_PACK_SELECT)
+ r = argument_pack_select_arg (t);
+ else if (TREE_CODE (t) == TREE_VEC)
+ r = preserve_args (t, cow_p);
+ else
+ r = t;
+ if (r != t)
+ {
+ if (cow_p)
+ {
+ args = copy_template_args (args);
+ cow_p = false;
+ }
+ TREE_VEC_ELT (args, i) = r;
+ }
+ }
+
+ return args;
+}
/* True iff FN is a function representing a built-in variadic parameter
pack. */
@@ -19511,10 +19546,11 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
LAMBDA_EXPR_MUTABLE_P (r) = LAMBDA_EXPR_MUTABLE_P (t);
if (tree ti = LAMBDA_EXPR_REGEN_INFO (t))
LAMBDA_EXPR_REGEN_INFO (r)
- = build_template_info (t, add_to_template_args (TI_ARGS (ti), args));
+ = build_template_info (t, add_to_template_args (TI_ARGS (ti),
+ preserve_args (args)));
else
LAMBDA_EXPR_REGEN_INFO (r)
- = build_template_info (t, args);
+ = build_template_info (t, preserve_args (args));
gcc_assert (LAMBDA_EXPR_THIS_CAPTURE (t) == NULL_TREE
&& LAMBDA_EXPR_PENDING_PROXIES (t) == NULL);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda19.C b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda19.C
new file mode 100644
index 00000000000..1921f4892fd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda19.C
@@ -0,0 +1,11 @@
+// PR c++/103706
+// { dg-do compile { target c++20 } }
+
+template<class T> concept C = __is_same(T, int);
+
+template<class... Ts> void f() {
+ ([]() requires C<Ts> { return Ts(); }(), ...); // { dg-error "no match" }
+}
+
+template void f<int, int, int>(); // { dg-bogus "" }
+template void f<int, int, char>(); // { dg-message "required from here" }
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