[gcc r11-4850] c++: Fix -Wvexing-parse ICE with omitted int [PR97762]

[gcc r11-4850] c++: Fix -Wvexing-parse ICE with omitted int [PR97762]

[Marek Polacek]

https://gcc.gnu.org/g:3a5f8d745f8e26d973218b088788f22ad197ca67

commit r11-4850-g3a5f8d745f8e26d973218b088788f22ad197ca67
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Nov 9 10:19:07 2020 -0500

    c++: Fix -Wvexing-parse ICE with omitted int [PR97762]
    
    For declarations like
    
      long f();
    
    decl_specifiers->type will be NULL, but I neglected to handle this case,
    therefore we ICE.  So handle this case by pretending we've seen 'int',
    which is good enough for -Wvexing-parse's purposes.
    
    gcc/cp/ChangeLog:
    
            PR c++/97762
            * parser.c (warn_about_ambiguous_parse): Handle the case when
            there is no type in the decl-specifiers.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/97762
            * g++.dg/warn/Wvexing-parse8.C: New test.

Diff:
---
 gcc/cp/parser.c                            | 23 +++++++++++++++++------
 gcc/testsuite/g++.dg/warn/Wvexing-parse8.C | 11 +++++++++++
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index bbf157eb47f..b14b4c90c92 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -20652,13 +20652,24 @@ warn_about_ambiguous_parse (const cp_decl_specifier_seq *decl_specifiers,
   if (declarator->parenthesized != UNKNOWN_LOCATION)
     return;
 
-  tree type = decl_specifiers->type;
-  if (TREE_CODE (type) == TYPE_DECL)
-   type = TREE_TYPE (type);
+  tree type;
+  if (decl_specifiers->type)
+    {
+      type = decl_specifiers->type;
+      if (TREE_CODE (type) == TYPE_DECL)
+	type = TREE_TYPE (type);
 
-  /* If the return type is void there is no ambiguity.  */
-  if (same_type_p (type, void_type_node))
-    return;
+      /* If the return type is void there is no ambiguity.  */
+      if (same_type_p (type, void_type_node))
+	return;
+    }
+  else
+    {
+      /* Code like long f(); will have null ->type.  If we have any
+	 type-specifiers, pretend we've seen int.  */
+      gcc_checking_assert (decl_specifiers->any_type_specifiers_p);
+      type = integer_type_node;
+    }
 
   auto_diagnostic_group d;
   location_t loc = declarator->u.function.parens_loc;
diff --git a/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C b/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C
new file mode 100644
index 00000000000..2d26d22fc4b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wvexing-parse8.C
@@ -0,0 +1,11 @@
+// PR c++/97762
+// { dg-do compile }
+
+void
+g ()
+{
+  long a(); // { dg-warning "empty parentheses" }
+  signed b(); // { dg-warning "empty parentheses" }
+  unsigned c(); // { dg-warning "empty parentheses" }
+  short d(); // { dg-warning "empty parentheses" }
+}