commit d3b4453834bb2e3cc1c875e76fe593c16f263f77
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Feb 16 16:53:47 2018 -0500

            PR c++/83911 - ICE with multiversioned constructor.
    
    gcc/
            * attribs.c (make_dispatcher_decl): Copy METHOD_TYPE,
            DECL_CXX_{CON,DE}STRUCTOR_P.
    gcc/cp/
            * cp-tree.h (DECL_CONSTRUCTOR_P): Use DECL_CXX_CONSTRUCTOR_P.
            (DECL_DESTRUCTOR_P): Use DECL_CXX_DESTRUCTOR_P.
            * mangle.c (write_unqualified_name): Check IDENTIFIER_[CD]TOR_P.

diff --git a/gcc/attribs.c b/gcc/attribs.c
index bfadf124dcb..2e9e69904f0 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -1063,9 +1063,14 @@ make_dispatcher_decl (const tree decl)
   func_name = xstrdup (IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (decl)));
 
   fn_type = TREE_TYPE (decl);
-  func_type = build_function_type (TREE_TYPE (fn_type),
-				   TYPE_ARG_TYPES (fn_type));
-  
+  if (TREE_CODE (fn_type) == METHOD_TYPE)
+    func_type = build_method_type_directly (TYPE_METHOD_BASETYPE (fn_type),
+					    TREE_TYPE (fn_type),
+					    TYPE_ARG_TYPES (fn_type));
+  else
+    func_type = build_function_type (TREE_TYPE (fn_type),
+				     TYPE_ARG_TYPES (fn_type));
+
   func_decl = build_fn_decl (func_name, func_type);
   XDELETEVEC (func_name);
   TREE_USED (func_decl) = 1;
@@ -1078,6 +1083,9 @@ make_dispatcher_decl (const tree decl)
   /* This will be of type IFUNCs have to be externally visible.  */
   TREE_PUBLIC (func_decl) = 1;
 
+  DECL_CXX_CONSTRUCTOR_P (func_decl) = DECL_CXX_CONSTRUCTOR_P (decl);
+  DECL_CXX_DESTRUCTOR_P (func_decl) = DECL_CXX_DESTRUCTOR_P (decl);
+
   return func_decl;  
 }
 
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 17d8c6d2650..268be0fd543 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -2695,7 +2695,7 @@ struct GTY(()) lang_decl {
 /* For FUNCTION_DECLs and TEMPLATE_DECLs: nonzero means that this function
    is a constructor.  */
 #define DECL_CONSTRUCTOR_P(NODE) \
-  IDENTIFIER_CTOR_P (DECL_NAME (NODE))
+  DECL_CXX_CONSTRUCTOR_P (STRIP_TEMPLATE (NODE))
 
 /* Nonzero if NODE (a FUNCTION_DECL) is a constructor for a complete
    object.  */
@@ -2724,7 +2724,7 @@ struct GTY(()) lang_decl {
 /* Nonzero if NODE (a FUNCTION_DECL or TEMPLATE_DECL)
    is a destructor.  */
 #define DECL_DESTRUCTOR_P(NODE)				\
-  IDENTIFIER_DTOR_P (DECL_NAME (NODE))
+  DECL_CXX_DESTRUCTOR_P (STRIP_TEMPLATE (NODE))
 
 /* Nonzero if NODE (a FUNCTION_DECL) is a destructor, but not the
    specialized in-charge constructor, in-charge deleting constructor,
diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 94c4bed2848..ecd4eb066d4 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -1351,9 +1351,9 @@ write_unqualified_name (tree decl)
   else if (DECL_DECLARES_FUNCTION_P (decl))
     {
       found = true;
-      if (DECL_CONSTRUCTOR_P (decl))
+      if (IDENTIFIER_CTOR_P (DECL_NAME (decl)))
 	write_special_name_constructor (decl);
-      else if (DECL_DESTRUCTOR_P (decl))
+      else if (IDENTIFIER_DTOR_P (DECL_NAME (decl)))
 	write_special_name_destructor (decl);
       else if (DECL_CONV_FN_P (decl))
 	{
diff --git a/gcc/testsuite/g++.dg/ext/mv27.C b/gcc/testsuite/g++.dg/ext/mv27.C
new file mode 100644
index 00000000000..443a54be765
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/mv27.C
@@ -0,0 +1,18 @@
+// PR c++/83911
+// { dg-do compile { target i?86-*-* x86_64-*-* } }
+// { dg-require-ifunc "" }
+
+class SimdFloat
+{
+public:
+    __attribute__ ((target ("default")))
+    SimdFloat(float x) {}
+
+    __attribute__ ((target ("avx2")))
+    SimdFloat(float x) {}
+};
+
+SimdFloat foo()
+{
+    return 1;
+}