Re: [PATCH] c++: Refine check for CTAD placeholder [PR99586]

[Jason Merrill via Gcc-patches]

On 4/1/21 10:30 AM, Patrick Palka wrote:

In the below testcase, during finish_compound_literal for A{},
type_uses_auto finds and returns the CTAD placeholder for B{V}, which
tricks us into attempting CTAD on A{} and leads to bogus errors.

AFAICT 'type' will always be a bare 'auto' in the CTAD case, so we don't
need to look deeply to find it; checking template_placeholder_p instead
should suffice here.

Bootstrapped and regtested on x86_64-pc-linux-gnu, and also on cmcstl2
and range-v3.  Does this look OK for trunk, or perhaps stage1?


OK for trunk.


gcc/cp/ChangeLog:

PR c++/99586
* semantics.c (finish_compound_literal): Check
template_placeholder_p instead of type_uses_auto.

gcc/testsuite/ChangeLog:

PR c++/99586
* g++.dg/cpp2a/nontype-class42.C: New test.
---
  gcc/cp/semantics.c   | 15 +++
  gcc/testsuite/g++.dg/cpp2a/nontype-class42.C |  8 
  2 files changed, 15 insertions(+), 8 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class42.C

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index b02596f73bd..8eaaaefe2d6 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -3036,14 +3036,13 @@ finish_compound_literal (tree type, tree 
compound_literal,
return error_mark_node;
  }
  
-  if (tree anode = type_uses_auto (type))

-if (CLASS_PLACEHOLDER_TEMPLATE (anode))
-  {
-   type = do_auto_deduction (type, compound_literal, anode, complain,
- adc_variable_type);
-   if (type == error_mark_node)
- return error_mark_node;
-  }
+  if (template_placeholder_p (type))
+{
+  type = do_auto_deduction (type, compound_literal, type, complain,
+   adc_variable_type);
+  if (type == error_mark_node)
+   return error_mark_node;
+}
  
/* Used to hold a copy of the compound literal in a template.  */

tree orig_cl = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C 
b/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C
new file mode 100644
index 000..a688bee6f3d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C
@@ -0,0 +1,8 @@
+// PR c++/99586
+// { dg-do compile { target c++20 } }
+
+template 
+struct B { constexpr B(T) { } };
+
+template  struct A{};
+template  auto a = A{};

[PATCH] c++: Refine check for CTAD placeholder [PR99586]

[Patrick Palka via Gcc-patches]

In the below testcase, during finish_compound_literal for A{},
type_uses_auto finds and returns the CTAD placeholder for B{V}, which
tricks us into attempting CTAD on A{} and leads to bogus errors.

AFAICT 'type' will always be a bare 'auto' in the CTAD case, so we don't
need to look deeply to find it; checking template_placeholder_p instead
should suffice here.

Bootstrapped and regtested on x86_64-pc-linux-gnu, and also on cmcstl2
and range-v3.  Does this look OK for trunk, or perhaps stage1?

gcc/cp/ChangeLog:

PR c++/99586
* semantics.c (finish_compound_literal): Check
template_placeholder_p instead of type_uses_auto.

gcc/testsuite/ChangeLog:

PR c++/99586
* g++.dg/cpp2a/nontype-class42.C: New test.
---
 gcc/cp/semantics.c   | 15 +++
 gcc/testsuite/g++.dg/cpp2a/nontype-class42.C |  8 
 2 files changed, 15 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class42.C

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index b02596f73bd..8eaaaefe2d6 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -3036,14 +3036,13 @@ finish_compound_literal (tree type, tree 
compound_literal,
   return error_mark_node;
 }
 
-  if (tree anode = type_uses_auto (type))
-if (CLASS_PLACEHOLDER_TEMPLATE (anode))
-  {
-   type = do_auto_deduction (type, compound_literal, anode, complain,
- adc_variable_type);
-   if (type == error_mark_node)
- return error_mark_node;
-  }
+  if (template_placeholder_p (type))
+{
+  type = do_auto_deduction (type, compound_literal, type, complain,
+   adc_variable_type);
+  if (type == error_mark_node)
+   return error_mark_node;
+}
 
   /* Used to hold a copy of the compound literal in a template.  */
   tree orig_cl = NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C 
b/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C
new file mode 100644
index 000..a688bee6f3d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class42.C
@@ -0,0 +1,8 @@
+// PR c++/99586
+// { dg-do compile { target c++20 } }
+
+template 
+struct B { constexpr B(T) { } };
+
+template  struct A{};
+template  auto a = A{};
-- 
2.31.1.133.g84d06cdc06