[PATCH] c++: ICE during constrained template friend matching [PR105064]

[PATCH] c++: ICE during constrained template friend matching [PR105064]

[Patrick Palka]

Here during declaration matching for the two constrained template
friends, we crash from maybe_substitute_reqs_for because the second
friend doesn't yet have DECL_TEMPLATE_INFO set (we're being called
indirectly from push_template_decl).

As far as I can tell, this situation happens only when declaring a
constrained template friend within a non-template class (as in the
testcase), in which case the substitution would be a no-op anyway, so it
should be safe to just skip it.  To that end this patch rearranges
maybe_substitute_reqs_for to gracefully handle DECL_TEMPLATE_INFO being
empty.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?

	PR c++/105064

gcc/cp/ChangeLog:

	* constraint.cc (maybe_substitute_reqs_for): Don't assume
	DECL_TEMPLATE_INFO is set.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-friend9.C: New test.
---
 gcc/cp/constraint.cc                          | 13 ++++---------
 gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C | 12 ++++++++++++
 2 files changed, 16 insertions(+), 9 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index e14578b1721..c5a991b9e71 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1268,20 +1268,15 @@ remove_constraints (tree t)
    for declaration matching.  */
 
 tree
-maybe_substitute_reqs_for (tree reqs, const_tree decl_)
+maybe_substitute_reqs_for (tree reqs, const_tree decl)
 {
   if (reqs == NULL_TREE)
     return NULL_TREE;
 
-  tree decl = CONST_CAST_TREE (decl_);
-  tree result = STRIP_TEMPLATE (decl);
-
-  if (DECL_UNIQUE_FRIEND_P (result))
+  decl = STRIP_TEMPLATE (decl);
+  if (DECL_UNIQUE_FRIEND_P (decl) && DECL_TEMPLATE_INFO (decl))
     {
-      tree tmpl = decl;
-      if (TREE_CODE (decl) != TEMPLATE_DECL)
-	tmpl = DECL_TI_TEMPLATE (result);
-
+      tree tmpl = DECL_TI_TEMPLATE (decl);
       tree gargs = generic_targs_for (tmpl);
       processing_template_decl_sentinel s;
       if (uses_template_parms (gargs))
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C
new file mode 100644
index 00000000000..09054d23d5d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C
@@ -0,0 +1,12 @@
+// PR c++/105064
+// { dg-do compile { target c++20 } }
+
+struct A {
+  template<class T>
+  friend void f(T) requires true;
+};
+
+struct B {
+  template<class T>
+  friend void f(T) requires true;
+};
-- 
2.35.1.677.gabf474a5dd

Re: [PATCH] c++: ICE during constrained template friend matching [PR105064]

[Jason Merrill]

On 3/28/22 09:29, Patrick Palka wrote:
> Here during declaration matching for the two constrained template
> friends, we crash from maybe_substitute_reqs_for because the second
> friend doesn't yet have DECL_TEMPLATE_INFO set (we're being called
> indirectly from push_template_decl).
> 
> As far as I can tell, this situation happens only when declaring a
> constrained template friend within a non-template class (as in the
> testcase), in which case the substitution would be a no-op anyway, so it
> should be safe to just skip it.  To that end this patch rearranges
> maybe_substitute_reqs_for to gracefully handle DECL_TEMPLATE_INFO being
> empty.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/11?

OK.

> 	PR c++/105064
> 
> gcc/cp/ChangeLog:
> 
> 	* constraint.cc (maybe_substitute_reqs_for): Don't assume
> 	DECL_TEMPLATE_INFO is set.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-friend9.C: New test.
> ---
>   gcc/cp/constraint.cc                          | 13 ++++---------
>   gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C | 12 ++++++++++++
>   2 files changed, 16 insertions(+), 9 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C
> 
> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
> index e14578b1721..c5a991b9e71 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -1268,20 +1268,15 @@ remove_constraints (tree t)
>      for declaration matching.  */
>   
>   tree
> -maybe_substitute_reqs_for (tree reqs, const_tree decl_)
> +maybe_substitute_reqs_for (tree reqs, const_tree decl)
>   {
>     if (reqs == NULL_TREE)
>       return NULL_TREE;
>   
> -  tree decl = CONST_CAST_TREE (decl_);
> -  tree result = STRIP_TEMPLATE (decl);
> -
> -  if (DECL_UNIQUE_FRIEND_P (result))
> +  decl = STRIP_TEMPLATE (decl);
> +  if (DECL_UNIQUE_FRIEND_P (decl) && DECL_TEMPLATE_INFO (decl))
>       {
> -      tree tmpl = decl;
> -      if (TREE_CODE (decl) != TEMPLATE_DECL)
> -	tmpl = DECL_TI_TEMPLATE (result);
> +      tree tmpl = DECL_TI_TEMPLATE (decl);
>         tree gargs = generic_targs_for (tmpl);
>         processing_template_decl_sentinel s;
>         if (uses_template_parms (gargs))
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C
> new file mode 100644
> index 00000000000..09054d23d5d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend9.C
> @@ -0,0 +1,12 @@
> +// PR c++/105064
> +// { dg-do compile { target c++20 } }
> +
> +struct A {
> +  template<class T>
> +  friend void f(T) requires true;
> +};
> +
> +struct B {
> +  template<class T>
> +  friend void f(T) requires true;
> +};