[gcc r12-8603] c++: cv-quals of dummy obj for non-dep memfn call [PR105637]

[gcc r12-8603] c++: cv-quals of dummy obj for non-dep memfn call [PR105637]

[Patrick Palka]

https://gcc.gnu.org/g:41487bff13fa98607ab5548bc1a0dca71147a5ac

commit r12-8603-g41487bff13fa98607ab5548bc1a0dca71147a5ac
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 3 12:06:59 2022 -0400

    c++: cv-quals of dummy obj for non-dep memfn call [PR105637]
    
    In non-dependent23.C below we expect the Base::foo calls to
    resolve to the second, third and fourth overloads respectively in light
    of the cv-qualifiers of 'this' in each case.  But ever since
    r12-6075-g2decd2cabe5a4f, the calls incorrectly resolve to the first
    overload at instantiation time.
    
    This happens because the calls to Base::foo are all deemed
    non-dependent (ever since r7-755-g23cb72663051cd made us ignore 'this'
    dependence when considering the dependence of a non-static memfn call),
    hence we end up checking the call ahead of time, using as the object
    argument a dummy object of type Base.  Since this object argument is
    cv-unqualified, the calls in turn resolve to the unqualified overload
    of baseDevice.  Before r12-6075 this incorrect result would just get
    silently discarded and we'd end up redoing OR at instantiation time
    using 'this' as the object argument.  But after r12-6075 we now reuse
    this incorrect result at instantiation time.
    
    This patch fixes this by making maybe_dummy_object respect the cv-quals
    of (the non-lambda) 'this' when returning a dummy object.  Thus, ahead
    of time OR using a dummy object will give us the right answer that's
    consistent with the instantiation time answer.
    
    An earlier version of this patch didn't handle 'this'-capturing lambdas
    correctly, which broke lambda-this22.C below.
    
            PR c++/105637
    
    gcc/cp/ChangeLog:
    
            * tree.cc (maybe_dummy_object): When returning a dummy
            object, respect the cv-quals of 'this' if available.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/lambda/lambda-this22.C: New test.
            * g++.dg/template/non-dependent23.C: New test.
    
    (cherry picked from commit 44a5bd6d933d86ed988fc4695aa00f122cf83eb4)

Diff:
---
 gcc/cp/tree.cc                                    | 30 +++++++++++++++++------
 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C | 20 +++++++++++++++
 gcc/testsuite/g++.dg/template/non-dependent23.C   | 25 +++++++++++++++++++
 3 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index ed0d0d22950..3b37567cbd7 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -4318,15 +4318,31 @@ maybe_dummy_object (tree type, tree* binfop)
   if (binfop)
     *binfop = binfo;
 
-  if (current_class_ref
-      /* current_class_ref might not correspond to current_class_type if
-	 we're in tsubst_default_argument or a lambda-declarator; in either
-	 case, we want to use current_class_ref if it matches CONTEXT.  */
-      && (same_type_ignoring_top_level_qualifiers_p
-	  (TREE_TYPE (current_class_ref), context)))
+  /* current_class_ref might not correspond to current_class_type if
+     we're in tsubst_default_argument or a lambda-declarator; in either
+     case, we want to use current_class_ref if it matches CONTEXT.  */
+  tree ctype = current_class_ref ? TREE_TYPE (current_class_ref) : NULL_TREE;
+  if (ctype
+      && same_type_ignoring_top_level_qualifiers_p (ctype, context))
     decl = current_class_ref;
   else
-    decl = build_dummy_object (context);
+    {
+      /* Return a dummy object whose cv-quals are consistent with (the
+	 non-lambda) 'this' if available.  */
+      if (ctype)
+	{
+	  int quals = TYPE_UNQUALIFIED;
+	  if (tree lambda = CLASSTYPE_LAMBDA_EXPR (ctype))
+	    {
+	      if (tree cap = lambda_expr_this_capture (lambda, false))
+		quals = cp_type_quals (TREE_TYPE (TREE_TYPE (cap)));
+	    }
+	  else
+	    quals = cp_type_quals (ctype);
+	  context = cp_build_qualified_type (context, quals);
+	}
+      decl = build_dummy_object (context);
+    }
 
   return decl;
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C
new file mode 100644
index 00000000000..8c6afe06cac
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-this22.C
@@ -0,0 +1,20 @@
+// PR c++/105637
+// { dg-do compile { target c++11 } }
+
+struct Base {
+  void foo();                // #1
+  void foo() const = delete; // #2
+};
+
+template<class T>
+struct TopClass : T {
+  void failsToCompile() {
+    [this] { Base::foo(); }(); // should select #2, not #1
+  }
+
+  void failsToCompile() const {
+    [this] { Base::foo(); }(); // { dg-error "deleted" }
+  }
+};
+
+template struct TopClass<Base>;
diff --git a/gcc/testsuite/g++.dg/template/non-dependent23.C b/gcc/testsuite/g++.dg/template/non-dependent23.C
new file mode 100644
index 00000000000..885a641a655
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent23.C
@@ -0,0 +1,25 @@
+// PR c++/105637
+
+struct Base {
+  void foo();                // #1
+  void foo() const;          // #2
+  void foo() volatile;       // #3
+  void foo() const volatile; // #4
+};
+
+template<class T>
+struct TopClass : T {
+  void failsToCompile() const {
+    Base::foo(); // should select #2, not #1
+  }
+
+  void failsToCompile() volatile {
+    Base::foo();  // should select #3, not #1
+  }
+
+  void failsToCompile() const volatile {
+    Base::foo();  // should select #4, not #1
+  }
+};
+
+template struct TopClass<Base>;