[gcc r11-8234] d: Add TARGET_D_TEMPLATES_ALWAYS_COMDAT

[gcc r11-8234] d: Add TARGET_D_TEMPLATES_ALWAYS_COMDAT

[Iain Buclaw]

https://gcc.gnu.org/g:bda519596543e49f77914b5677693e86be5d01d0

commit r11-8234-gbda519596543e49f77914b5677693e86be5d01d0
Author: Iain Buclaw <ibuclaw@gdcproject.org>
Date:   Tue Apr 13 22:28:55 2021 +0200

    d: Add TARGET_D_TEMPLATES_ALWAYS_COMDAT
    
    Following up on the fix for PR99914, when testing on MinGW, it was found
    not to support weak in the same way as on ELF or Mach-O targets.
    
    So the linkage has been reverted back to COMDAT for that target, however
    in order to properly support overriding functions and variables, all
    declarations with external linkage must be put on COMDAT.  For this a
    new target hook has been added to control the behavior.
    
    gcc/ChangeLog:
    
            PR d/99914
            * config/i386/winnt-d.c (TARGET_D_TEMPLATES_ALWAYS_COMDAT): Define.
            * doc/tm.texi: Regenerate.
            * doc/tm.texi.in (D language and ABI): Add @hook for
            TARGET_D_TEMPLATES_ALWAYS_COMDAT.
    
    gcc/d/ChangeLog:
    
            PR d/99914
            * d-target.def (d_templates_always_comdat): New hook.
            * d-tree.h (mark_needed): Remove prototype.
            * decl.cc: Include d-target.h.
            (mark_needed): Rename to...
            (d_mark_needed): ...this.  Make static.
            (set_linkage_for_decl): Put variables in comdat if
            d_templates_always_comdat.

Diff:
---
 gcc/config/i386/winnt-d.c |  5 +++++
 gcc/d/d-target.def        |  8 ++++++++
 gcc/d/d-tree.h            |  1 -
 gcc/d/decl.cc             | 17 +++++++++++++++--
 gcc/doc/tm.texi           |  6 ++++++
 gcc/doc/tm.texi.in        |  2 ++
 6 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/gcc/config/i386/winnt-d.c b/gcc/config/i386/winnt-d.c
index b9780258549..ea4cd13d0bf 100644
--- a/gcc/config/i386/winnt-d.c
+++ b/gcc/config/i386/winnt-d.c
@@ -78,4 +78,9 @@ winnt_d_register_target_info (void)
 #undef TARGET_D_MINFO_END_NAME
 #define TARGET_D_MINFO_END_NAME "__stop_minfo"
 
+/* Define TARGET_D_TEMPLATES_ALWAYS_COMDAT for Windows targets.  */
+
+#undef TARGET_D_TEMPLATES_ALWAYS_COMDAT
+#define TARGET_D_TEMPLATES_ALWAYS_COMDAT true
+
 struct gcc_targetdm targetdm = TARGETDM_INITIALIZER;
diff --git a/gcc/d/d-target.def b/gcc/d/d-target.def
index aa6bf55e6e6..67647515cf2 100644
--- a/gcc/d/d-target.def
+++ b/gcc/d/d-target.def
@@ -104,5 +104,13 @@ and @var{link_windows} to @code{1} to apply @code{stdcall} to functions with\n\
  bool, (unsigned int *link_system, unsigned int *link_windows),
  hook_bool_uintp_uintp_false)
 
+/* True if instantiations are always COMDAT if they have external linkage.  */
+DEFHOOKPOD
+(d_templates_always_comdat,
+ "This flag is true if instantiated functions and variables are always COMDAT\n\
+if they have external linkage.  If this flag is false, then instantiated\n\
+decls will be emitted as weak symbols.  The default is @code{false}.",
+ bool, false)
+
 /* Close the 'struct gcc_targetdm' definition.  */
 HOOK_VECTOR_END (C90_EMPTY_HACK)
diff --git a/gcc/d/d-tree.h b/gcc/d/d-tree.h
index c1b6f275149..bb731a60541 100644
--- a/gcc/d/d-tree.h
+++ b/gcc/d/d-tree.h
@@ -631,7 +631,6 @@ extern void d_finish_decl (tree);
 extern tree make_thunk (FuncDeclaration *, int);
 extern tree start_function (FuncDeclaration *);
 extern void finish_function (tree);
-extern void mark_needed (tree);
 extern tree get_vtable_decl (ClassDeclaration *);
 extern tree build_new_class_expr (ClassReferenceExp *);
 extern tree aggregate_initializer_decl (AggregateDeclaration *);
diff --git a/gcc/d/decl.cc b/gcc/d/decl.cc
index 8948e40e902..7d1378255bd 100644
--- a/gcc/d/decl.cc
+++ b/gcc/d/decl.cc
@@ -59,6 +59,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "symtab-thunks.h"
 
 #include "d-tree.h"
+#include "d-target.h"
 
 
 /* Return identifier for the external mangled name of DECL.  */
@@ -1960,8 +1961,8 @@ finish_function (tree old_context)
 /* Mark DECL, which is a VAR_DECL or FUNCTION_DECL as a symbol that
    must be emitted in this, output module.  */
 
-void
-mark_needed (tree decl)
+static void
+d_mark_needed (tree decl)
 {
   TREE_USED (decl) = 1;
 
@@ -2380,6 +2381,18 @@ set_linkage_for_decl (tree decl)
   if (TREE_CODE (decl) == FUNCTION_DECL && DECL_DECLARED_INLINE_P (decl))
     return d_comdat_linkage (decl);
 
+  /* If all instantiations must go in COMDAT, give them that linkage.
+     This also applies to other extern declarations, so that it is possible
+     for them to override template declarations.  */
+  if (targetdm.d_templates_always_comdat)
+    {
+      /* Make sure that instantiations are not removed.  */
+      if (flag_weak_templates && DECL_INSTANTIATED (decl))
+	d_mark_needed (decl);
+
+      return d_comdat_linkage (decl);
+    }
+
   /* Instantiated variables and functions need to be overridable by any other
      symbol with the same name, so give them weak linkage.  */
   if (DECL_INSTANTIATED (decl))
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 97c8eebcd6f..823f85ba9ab 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -10850,6 +10850,12 @@ and @var{link_windows} to @code{1} to apply @code{stdcall} to functions with
 @code{extern(Windows)} linkage.
 @end deftypefn
 
+@deftypevr {D Target Hook} bool TARGET_D_TEMPLATES_ALWAYS_COMDAT
+This flag is true if instantiated functions and variables are always COMDAT
+if they have external linkage.  If this flag is false, then instantiated
+decls will be emitted as weak symbols.  The default is @code{false}.
+@end deftypevr
+
 @node Named Address Spaces
 @section Adding support for named address spaces
 @cindex named address spaces
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index e2d49ee9f57..2321a5fc4e0 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7369,6 +7369,8 @@ floating-point support; they are not included in this mechanism.
 
 @hook TARGET_D_HAS_STDCALL_CONVENTION
 
+@hook TARGET_D_TEMPLATES_ALWAYS_COMDAT
+
 @node Named Address Spaces
 @section Adding support for named address spaces
 @cindex named address spaces