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C++ PATCH for c++/83947, ICE with auto deduction

Message ID CADzB+2=52_oR-MMZdCPmWPjz=oNazRAcyDEQm+JrsLJDHfqiQA@mail.gmail.com
State New
Headers show
Series C++ PATCH for c++/83947, ICE with auto deduction | expand

Commit Message

Jason Merrill Jan. 23, 2018, 9:18 p.m. UTC 
In this testcase, we were deducing a type for g from the function f
which has not yet been deduced itself.  Fixed by recognizing the case
of an undeduced initializer.

The change to undeduced_auto_decl is necessary because auto parameters
are a different story; they act more like normal template parameters.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit 28ec0bede14adc98ac9cec6693f8a4c0ccf39d14
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Jan 23 13:47:13 2018 -0500

            PR c++/83947 - ICE with auto declarations.
    
            * pt.c (do_auto_deduction): Don't deduce from an auto decl.
            * decl.c (undeduced_auto_decl): Limit to vars and fns.
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Patch

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index f6fab422d17..e6d9289abd2 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -16189,15 +16189,17 @@  fndecl_declared_return_type (tree fn)
   return TREE_TYPE (TREE_TYPE (fn));
 }
 
-/* Returns true iff DECL was declared with an auto type and it has
-   not yet been deduced to a real type.  */
+/* Returns true iff DECL is a variable or function declared with an auto type
+   that has not yet been deduced to a real type.  */
 
 bool
 undeduced_auto_decl (tree decl)
 {
   if (cxx_dialect < cxx11)
     return false;
-  return type_uses_auto (TREE_TYPE (decl));
+  return ((VAR_OR_FUNCTION_DECL_P (decl)
+	   || TREE_CODE (decl) == TEMPLATE_DECL)
+	  && type_uses_auto (TREE_TYPE (decl)));
 }
 
 /* Complain if DECL has an undeduced return type.  */
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 0296845a31b..d5d263c1c74 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25891,6 +25891,10 @@  do_auto_deduction (tree type, tree init, tree auto_node,
        from ahead of time isn't worth the trouble.  */
     return type;
 
+  /* Similarly, we can't deduce from another undeduced decl.  */
+  if (init && undeduced_auto_decl (init))
+    return type;
+
   if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
     /* C++17 class template argument deduction.  */
     return do_class_deduction (type, tmpl, init, flags, complain);
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn46.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn46.C
new file mode 100644
index 00000000000..120a4dd9e7c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn46.C
@@ -0,0 +1,6 @@ 
+// PR c++/83947
+// { dg-do compile { target c++14 } }
+
+auto f ();
+template < int > auto g (f);	// { dg-error "before deduction" }
+auto h = g < 0 > ();