Re: RFC: -fno-share-inlines

[Allan Sandfeld Jensen]

On Montag, 24. August 2020 08:52:04 CEST Richard Biener wrote:
> On Mon, Aug 10, 2020 at 9:36 AM Allan Sandfeld Jensen
> 
>  wrote:
> > Following the previous discussion, this is a proposal for a patch that
> > adds
> > the flag -fno-share-inlines that can be used when compiling singular
> > source
> > files with a different set of flags than the rest of the project.
> > 
> > It basically turns off comdat for inline functions, as if you compiled
> > without support for 'weak' symbols. Turning them all into "static"
> > functions, even if that wouldn't normally be possible for that type of
> > function. Not sure if it breaks anything, which is why I am not sending
> > it to the patch list.
> > 
> > I also considered alternatively to turn the comdat generation off later
> > during assembler production to ensure all processing and optimization of
> > comdat functions would occur as normal.
> 
> We already have -fvisibility-inlines-hidden so maybe call it
> -fvisibility-inlines-static?
That could make sense.

> Does this option also imply 'static' vtables?
> 
I don't think so. It affects functions declarations. It probably also affect 
virtual functions, but as far as I know the place changed only affects the 
functions not the virtual table. So there could still be a duplicated virtual 
table with the wrong methods, that then depends on linking if it will be used 
globally. I am not sure I dare change that, having different virtual tables 
for the same class depending on where it is allocated sounds like a way to 
break some things.

I wouldn't use virtual tables anyway when dealing with mixed architectures.

Best regards
Allan

Re: RFC: -fno-share-inlines

[Richard Biener via Gcc]

On Mon, Aug 10, 2020 at 9:36 AM Allan Sandfeld Jensen
 wrote:
>
> Following the previous discussion, this is a proposal for a patch that adds
> the flag -fno-share-inlines that can be used when compiling singular source
> files with a different set of flags than the rest of the project.
>
> It basically turns off comdat for inline functions, as if you compiled without
> support for 'weak' symbols. Turning them all into "static" functions, even if
> that wouldn't normally be possible for that type of function. Not sure if it
> breaks anything, which is why I am not sending it to the patch list.
>
> I also considered alternatively to turn the comdat generation off later during
> assembler production to ensure all processing and optimization of comdat
> functions would occur as normal.

We already have -fvisibility-inlines-hidden so maybe call it
-fvisibility-inlines-static?
Does this option also imply 'static' vtables?

Richard.

> Best regards
> Allan

RFC: -fno-share-inlines

[Allan Sandfeld Jensen]

Following the previous discussion, this is a proposal for a patch that adds 
the flag -fno-share-inlines that can be used when compiling singular source 
files with a different set of flags than the rest of the project.

It basically turns off comdat for inline functions, as if you compiled without 
support for 'weak' symbols. Turning them all into "static" functions, even if 
that wouldn't normally be possible for that type of function. Not sure if it 
breaks anything, which is why I am not sending it to the patch list.

I also considered alternatively to turn the comdat generation off later during 
assembler production to ensure all processing and optimization of comdat 
functions would occur as normal.

Best regards
Allandiff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 2b1aca16eb4..78e1f592126 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1803,6 +1803,10 @@ frtti
 C++ ObjC++ Optimization Var(flag_rtti) Init(1)
 Generate run time type descriptor information.

+fshare-inlines
+C C++ ObjC ObjC++ Var(flag_share_inlines) Init(1)
+Emit non-inlined inlined declared functions to be shared between object files.
+
 fshort-enums
 C ObjC C++ ObjC++ LTO Optimization Var(flag_short_enums)
 Use the narrowest integer type possible for enumeration types.
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index 33c83773d33..8de796d16fc 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -1957,10 +1957,9 @@ adjust_var_decl_tls_model (tree decl)
 void
 comdat_linkage (tree decl)
 {
-  if (flag_weak)
-make_decl_one_only (decl, cxx_comdat_group (decl));
-  else if (TREE_CODE (decl) == FUNCTION_DECL
-	   || (VAR_P (decl) && DECL_ARTIFICIAL (decl)))
+  if ((!flag_share_inlines || !flag_weak)
+  && (TREE_CODE (decl) == FUNCTION_DECL
+	  || (VAR_P (decl) && DECL_ARTIFICIAL (decl
 /* We can just emit function and compiler-generated variables
statically; having multiple copies is (for the most part) only
a waste of space.
@@ -1978,6 +1977,8 @@ comdat_linkage (tree decl)
should perform a string comparison, rather than an address
comparison.  */
 TREE_PUBLIC (decl) = 0;
+  else if (flag_weak)
+make_decl_one_only (decl, cxx_comdat_group (decl));
   else
 {
   /* Static data member template instantiations, however, cannot