Re: [PATCH] C++: target attribute - local decl

["Martin Liška" <mliska@suse.cz>]

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On 3/2/21 6:57 PM, Jason Merrill wrote:
> On 3/2/21 5:34 AM, Martin Liška wrote:
>> On 3/1/21 8:58 PM, Jason Merrill wrote:
>>> On 3/1/21 11:59 AM, Martin Liška wrote:
>>>> On 3/1/21 5:36 PM, Jason Merrill wrote:
>>>>> On 3/1/21 7:43 AM, Martin Liška wrote:
>>>>>> On 2/22/21 11:53 PM, Jason Merrill wrote:
>>>>>>> The problem seems to be with the handling of local decls.  If DECL_LOCAL_DECL_P, you need to look at DECL_LOCAL_DECL_ALIAS to find the namespace-scope decl.  But then if there is no preceding namespace-scope declaration, the new decl created by push_local_extern_decl_alias doesn't have a cgraph node, either. I guess maybe_function_versions also needs to look through DECL_LOCAL_DECL_ALIAS.
>>>>>>
>>>>>> Ah, I see. Are you sure about the name 'maybe_function_versions'? I can't find it.
>>>>>
>>>>> Ah, it's maybe_version_functions, sorry.
>>>>
>>>> Thanks, I see the function now.
>>>> So about your guess:
>>>>
>>>>> I guess maybe_function_versions also needs to look through DECL_LOCAL_DECL_ALIAS.
>>>>
>>>> Do you mean maybe_version_functions's argument 'record' should depend on DECL_LOCAL_DECL_ALIAS of newdecl/oldddecl
>>>> (if present)? Or that DECL_FUNCTION_VERSIONED should be set for DECL_LOCAL_DECL_ALIASes of the newdecl/olddecl
>>>> function declarations?
>>>
>>> The latter.
>>
>> I see, but will not help us. Problem is that
>> #2  0x00000000015d8899 in ix86_get_function_versions_dispatcher (decl=0x7ffff7755000) at /home/marxin/Programming/gcc/gcc/config/i386/i386-features.c:2862
>>
>> is called for a declaration for which
>>
>> Breakpoint 5, maybe_version_functions (newdecl=<function_decl 0x7ffff7755000 f>, olddecl=<function_decl 0x7ffff7751f00 f>, record=false) at /home/marxin/Programming/gcc/gcc/cp/decl.c:1118
>>
>> is called with record=false. So that cgraph_node is not created for it.
>>
>> Or is a possible solution that get_function_version_dispatcher should look through the DECL_LOCAL_DECL_ALIAS?
> 
> Yes, I was thinking both that function and maybe_version_functions.
> 
> Jason
> 

All right, the following patch fixes that.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

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From ffff192a6ad5840c425a940ac724e27e0d25f7b0 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Wed, 3 Mar 2021 09:38:55 +0100
Subject: [PATCH] c++: support target attr for DECL_LOCAL_DECL_P fns

gcc/cp/ChangeLog:

	PR c++/99108
	* call.c (get_function_version_dispatcher): Understand
	DECL_LOCAL_DECL_ALIAS.
	* decl.c (record_function_versions): New.
	(maybe_version_functions): Call record_function_versions
	for both declarations and DECL_LOCAL_DECL_ALIAS aliases.

gcc/testsuite/ChangeLog:

	PR c++/99108
	* g++.target/i386/pr99108.C: New test.
---
 gcc/cp/call.c                           |  4 +++
 gcc/cp/decl.c                           | 40 +++++++++++++++----------
 gcc/testsuite/g++.target/i386/pr99108.C | 18 +++++++++++
 3 files changed, 47 insertions(+), 15 deletions(-)
 create mode 100644 gcc/testsuite/g++.target/i386/pr99108.C

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 123f06b1f2b..117f1755191 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -8467,6 +8467,10 @@ get_function_version_dispatcher (tree fn)
 {
   tree dispatcher_decl = NULL;
 
+  if (DECL_LOCAL_DECL_P (fn)
+      && DECL_LOCAL_DECL_ALIAS (fn) != NULL_TREE)
+    fn = DECL_LOCAL_DECL_ALIAS (fn);
+
   gcc_assert (TREE_CODE (fn) == FUNCTION_DECL
 	      && DECL_FUNCTION_VERSIONED (fn));
 
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 1742e286d9f..69bf3011a5a 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -1108,6 +1108,23 @@ decls_match (tree newdecl, tree olddecl, bool record_versions /* = true */)
   return types_match;
 }
 
+/* Register function version for DECL that would point to VERSION.
+   If RECORD set to true, register function version in call graph.  */
+
+static void
+record_function_versions (tree decl, tree version, bool record)
+{
+  if (!DECL_FUNCTION_VERSIONED (version))
+    {
+      DECL_FUNCTION_VERSIONED (version) = 1;
+      if (DECL_ASSEMBLER_NAME_SET_P (version))
+	mangle_decl (version);
+    }
+
+  if (record && decl != version)
+    cgraph_node::record_function_versions (decl, version);
+}
+
 /* NEWDECL and OLDDECL have identical signatures.  If they are
    different versions adjust them and return true.
    If RECORD is set to true, record function versions.  */
@@ -1118,22 +1135,15 @@ maybe_version_functions (tree newdecl, tree olddecl, bool record)
   if (!targetm.target_option.function_versions (newdecl, olddecl))
     return false;
 
-  if (!DECL_FUNCTION_VERSIONED (olddecl))
-    {
-      DECL_FUNCTION_VERSIONED (olddecl) = 1;
-      if (DECL_ASSEMBLER_NAME_SET_P (olddecl))
-	mangle_decl (olddecl);
-    }
-
-  if (!DECL_FUNCTION_VERSIONED (newdecl))
-    {
-      DECL_FUNCTION_VERSIONED (newdecl) = 1;
-      if (DECL_ASSEMBLER_NAME_SET_P (newdecl))
-	mangle_decl (newdecl);
-    }
+  record_function_versions (olddecl, olddecl, record);
+  if (DECL_LOCAL_DECL_P (olddecl)
+      && DECL_LOCAL_DECL_ALIAS (olddecl) != NULL_TREE)
+    record_function_versions (olddecl, DECL_LOCAL_DECL_ALIAS (olddecl), true);
 
-  if (record)
-    cgraph_node::record_function_versions (olddecl, newdecl);
+  record_function_versions (olddecl, newdecl, record);
+  if (DECL_LOCAL_DECL_P (newdecl)
+      && DECL_LOCAL_DECL_ALIAS (newdecl) != NULL_TREE)
+    record_function_versions (olddecl, DECL_LOCAL_DECL_ALIAS (newdecl), true);
 
   return true;
 }
diff --git a/gcc/testsuite/g++.target/i386/pr99108.C b/gcc/testsuite/g++.target/i386/pr99108.C
new file mode 100644
index 00000000000..ad9409b8799
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr99108.C
@@ -0,0 +1,18 @@
+/* PR c++/99108 */
+/* { dg-do compile { target c++20 } } */
+/* { dg-require-ifunc "" }  */
+
+struct A {
+  void foo(auto);
+};
+void A::foo(auto)
+{
+  int f(void) __attribute__((target("default")));
+  int f(void) __attribute__((target("arch=atom")));
+  int b = f();
+}
+void bar(void)
+{
+  A c;
+  c.foo(7);
+}
-- 
2.30.1