C++ PATCH for c++/77775 (wrong folding of PMF comparison)

[Jason Merrill]

The RECORD_TYPE for a PMF does not have variants in the usual way;
rather, a variant PMF will have a distinct RECORD_TYPE where the pfn
field has a variant type.  As a result, if we cast a constant PMF to a
variant type, we will end up looking up a different field than we
initialized.  Deal with this by using field names for PMFs.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit f412d0f7919501f9cff962858975cfa48cd4d274
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Sep 30 17:00:11 2016 -0400

            PR c++/77775 - misoptimization of PMF comparison
    
            * constexpr.c (cxx_eval_component_reference): Use name matching
            for PMFs.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 2db13d2..4acbb26 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2315,9 +2315,13 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, 
tree t,
     }
   if (*non_constant_p)
     return t;
+  bool pmf = TYPE_PTRMEMFUNC_P (TREE_TYPE (whole));
   FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (whole), i, field, value)
     {
-      if (field == part)
+      /* Use name match for PMF fields, as a variant will have a
+        different FIELD_DECL with a different type.  */
+      if (pmf ? DECL_NAME (field) == DECL_NAME (part)
+         : field == part)
        {
          if (value)
            return value;
@@ -2342,6 +2346,8 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, 
tree t,
   if (is_really_empty_class (TREE_TYPE (t)))
     return build_constructor (TREE_TYPE (t), NULL);
 
+  gcc_assert (DECL_CONTEXT (part) == TYPE_MAIN_VARIANT (TREE_TYPE (whole)));
+
   if (CONSTRUCTOR_NO_IMPLICIT_ZERO (whole))
     {
       /* 'whole' is part of the aggregate initializer we're currently
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf1.C 
b/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf1.C
new file mode 100644
index 0000000..b6a7935
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-pmf1.C
@@ -0,0 +1,17 @@
+// PR c++/77775
+// { dg-options -fdump-tree-gimple }
+// { dg-final { scan-tree-dump "== viewAdded" "gimple" { target c++11 } } }
+
+namespace Sublime {
+struct View;
+struct AreaIndex;
+struct Area {
+  void qt_static_metacall();
+  void viewAdded(AreaIndex *, View *);
+};
+}
+void Sublime::Area::qt_static_metacall() {
+  typedef void (Area::*_t)(AreaIndex *, View *);
+  if (*reinterpret_cast<_t *>(1) == _t(&Area::viewAdded))
+    __builtin_abort();
+}