On Wed, 30 Sep 2020, Jason Merrill wrote:
> On 9/29/20 5:01 PM, Patrick Palka wrote:
> > This patch fixes an "unguarded" call to coerce_template_parms in
> > build_standard_check: processing_template_decl could be zero if we
> > we get here during processing of the first 'auto' parameter of an
> > abbreviated function template. In the testcase below, this leads to an
> > ICE when coerce_template_parms substitutes into C's dependent default
> > template argument.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu and tested by building
> > cmcstl2 and range-v3. Does this look OK for trunk?
>
> This looks OK, but is there a place higher in the call stack where we should
> have already set processing_template_decl?
The call stack at that point is:
build_variable_check
build_concept_check
build_type_constraint
finish_type_constraints
cp_parser_placeholder_type_specifier
cp_parser_simple_type_specifier
...
So it seems the most natural place to set processing_template_decl would
be in build_type_constraint, around the call to build_concept_check,
since that's where we create the WILDCARD_DECL that eventually reaches
coerce_template_parms.
And in order to additionally avoid a similar ICE when processing the
type constraint of a non-templated variable, we also need to guard the
call to build_concept check in make_constrained_placeholder_type. The
testcase below now contains such an example.
So something like this perhaps:
-- >8 --
Subject: [PATCH] c++: ICE in dependent_type_p with constrained auto [PR97052]
This patch fixes an "unguarded" call to coerce_template_parms in
build_standard_check: processing_template_decl could be zero if we
get here during processing of the first 'auto' parameter of an
abbreviated function template, or if we're processing the type
constraint of a non-templated variable. In the testcase below, this
leads to an ICE when coerce_template_parms instantiates C's dependent
default template argument.
gcc/cp/ChangeLog:
PR c++/97052
* constraint.cc (build_type_constraint): Temporarily increment
processing_template_decl before calling build_concept_check.
* pt.c (make_constrained_placeholder_type): Likewise.
gcc/testsuite/ChangeLog:
PR c++/97052
* g++.dg/cpp2a/concepts-defarg2: New test.
---
gcc/cp/constraint.cc | 2 ++
gcc/cp/pt.c | 2 ++
gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C | 13 +++++++++++++
3 files changed, 17 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index d49957a6c4a..050b55ce092 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1427,7 +1427,9 @@ tree
build_type_constraint (tree decl, tree args, tsubst_flags_t complain)
{
tree wildcard = build_nt (WILDCARD_DECL);
+ ++processing_template_decl;
tree check = build_concept_check (decl, wildcard, args, complain);
+ --processing_template_decl;
if (check == error_mark_node)
return error_mark_node;
return unpack_concept_check (check);
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 72efecff37f..efdd017a4d5 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -27914,7 +27914,9 @@ make_constrained_placeholder_type (tree type, tree con,
tree args)
tree expr = tmpl;
if (TREE_CODE (con) == FUNCTION_DECL)
expr = ovl_make (tmpl);
+ ++processing_template_decl;
expr = build_concept_check (expr, type, args, tf_warning_or_error);
+ --processing_template_decl;
PLACEHOLDER_TYPE_CONSTRAINTS (type) = expr;
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
new file mode 100644
index 00000000000..a63ca4e133d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-defarg2.C
@@ -0,0 +1,13 @@
+// PR c++/97052
+// { dg-do compile { target c++20 } }
+
+template<typename T, typename U = typename T::type>
+concept C = true;
+
+constexpr bool f(C auto) {
+ return true;
+}
+
+static_assert(f(0));
+
+C auto x = 0;
--
2.28.0.715.gab4691b67b
