Re: RFA (make_dispatcher_decl): PATCH for c++/83911, ICE with multiversioned constructor

[Jason Merrill <jason at redhat dot com>]

On Thu, Mar 15, 2018 at 4:50 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Mar 14, 2018 at 8:57 PM, Jason Merrill <jason@redhat.com> wrote:
>> Ping
>>
>> On Fri, Mar 2, 2018 at 1:23 PM, Jason Merrill <jason@redhat.com> wrote:
>>> As I mentioned in the PR, the problem here is that we're replacing a
>>> constructor with a dispatcher function which doesn't look much like a
>>> constructor.  This patch adjusts make_dispatcher_decl to make it look
>>> more like the functions it dispatches to, but other things are certain
>>> to break for similar reasons down the road.  A proper solution should
>>> be more transparent, like thunks.
>>>
>>> Tested x86_64-pc-linux-gnu.  Does this seem worth applying to fix the
>>> regression?
>
> The patch looks reasonable to me, you probably know best whether
> the cp/ parts are risky or not ;)
>
> So - OK from my POV.
>
> And yes, thunks may be a better representation for the dispatcher.

It occurred to me that I could handle this more locally by deferring
the function substitution until genericization time, so this is what
I'm checking in:

commit 05dda93e56e02859c65f93bd541dc7793bc7305c
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Feb 16 16:53:47 2018 -0500

            PR c++/83911 - ICE with multiversioned constructor.
    
            * cp-gimplify.c (cp_genericize_r): Replace versioned function with
            dispatchere here.
            * call.c (build_over_call): Not here.
            PR c++/83911 - ICE with multiversioned constructor.

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 45c22aaa312..67438ff2e94 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -8204,23 +8204,6 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
 	}
     }
 
-  /* For calls to a multi-versioned function, overload resolution
-     returns the function with the highest target priority, that is,
-     the version that will checked for dispatching first.  If this
-     version is inlinable, a direct call to this version can be made
-     otherwise the call should go through the dispatcher.  */
-
-  if (DECL_FUNCTION_VERSIONED (fn)
-      && (current_function_decl == NULL
-	  || !targetm.target_option.can_inline_p (current_function_decl, fn)))
-    {
-      fn = get_function_version_dispatcher (fn);
-      if (fn == NULL)
-	return NULL;
-      if (!already_used)
-	mark_versions_used (fn);
-    }
-
   if (!already_used
       && !mark_used (fn, complain))
     return error_mark_node;
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index 0ddd435454c..653d1dcee26 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -1513,6 +1513,29 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
 		       == REFERENCE_TYPE))
 	    *walk_subtrees = 0;
 	}
+      /* Fall through.  */
+    case AGGR_INIT_EXPR:
+      /* For calls to a multi-versioned function, overload resolution
+	 returns the function with the highest target priority, that is,
+	 the version that will checked for dispatching first.  If this
+	 version is inlinable, a direct call to this version can be made
+	 otherwise the call should go through the dispatcher.  */
+      {
+	tree fn = cp_get_callee_fndecl (stmt);
+	if (fn && DECL_FUNCTION_VERSIONED (fn)
+	    && (current_function_decl == NULL
+		|| !targetm.target_option.can_inline_p (current_function_decl,
+							fn)))
+	  if (tree dis = get_function_version_dispatcher (fn))
+	    {
+	      mark_versions_used (dis);
+	      dis = build_address (dis);
+	      if (TREE_CODE (stmt) == CALL_EXPR)
+		CALL_EXPR_FN (stmt) = dis;
+	      else
+		AGGR_INIT_EXPR_FN (stmt) = dis;
+	    }
+      }
       break;
 
     default:
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;
+}