[PATCH] c++, v5: Retry the aliasing of base/complete cdtor optimization at import_export_decl time [PR113208]

[Jakub Jelinek <jakub@redhat.com>]

On Thu, Apr 25, 2024 at 11:30:48AM -0400, Jason Merrill wrote:
> Hmm, maybe maybe_clone_body shouldn't clear DECL_SAVED_TREE for aliases, but
> rather set it to some stub like void_node?

I'll try that in stage1.

> Though with all these changes, it's probably better to go with your first
> patch for GCC 14 and delay this approach to 15.  Your v1 patch is OK for 14.

Just to record, following patch passed bootstrap/regtest on x86_64-linux and
i686-linux.  But I've committed the v1 version instead with the addition of
comdat2.C and comdat5.C testcases from this patch now and in stage1 will
post an incremental diff.

Thanks.

2024-04-25  Jakub Jelinek  <jakub@redhat.com>
	    Jason Merrill  <jason@redhat.com>

	PR lto/113208
	* decl2.cc (tentative_decl_linkage): Call maybe_make_one_only
	for implicit instantiations of maybe in charge ctors/dtors
	declared inline.
	(c_parse_final_cleanups): Don't skip used same body aliases which
	have non-NULL DECL_SAVED_TREE on the alias target.  Formatting fixes.
	* optimize.cc (can_alias_cdtor): Adjust condition, for
	HAVE_COMDAT_GROUP && DECL_ONE_ONLY && DECL_WEAK return true even
	if not DECL_INTERFACE_KNOWN.
	* decl.cc (cxx_comdat_group): For DECL_CLONED_FUNCTION_P
	functions if SUPPORTS_ONE_ONLY return DECL_COMDAT_GROUP if already
	set.

	* g++.dg/abi/comdat2.C: New test.
	* g++.dg/abi/comdat3.C: New test.
	* g++.dg/abi/comdat4.C: New test.
	* g++.dg/abi/comdat5.C: New test.
	* g++.dg/lto/pr113208_0.C: New test.
	* g++.dg/lto/pr113208_1.C: New file.
	* g++.dg/lto/pr113208.h: New file.

--- gcc/cp/decl2.cc.jj	2024-04-24 18:28:22.299513620 +0200
+++ gcc/cp/decl2.cc	2024-04-25 16:19:17.385547357 +0200
@@ -3312,16 +3312,23 @@ tentative_decl_linkage (tree decl)
 	     linkage of all functions, and as that causes writes to
 	     the data mapped in from the PCH file, it's advantageous
 	     to mark the functions at this point.  */
-	  if (DECL_DECLARED_INLINE_P (decl)
-	      && (!DECL_IMPLICIT_INSTANTIATION (decl)
-		  || DECL_DEFAULTED_FN (decl)))
+	  if (DECL_DECLARED_INLINE_P (decl))
 	    {
-	      /* This function must have external linkage, as
-		 otherwise DECL_INTERFACE_KNOWN would have been
-		 set.  */
-	      gcc_assert (TREE_PUBLIC (decl));
-	      comdat_linkage (decl);
-	      DECL_INTERFACE_KNOWN (decl) = 1;
+	      if (!DECL_IMPLICIT_INSTANTIATION (decl)
+		  || DECL_DEFAULTED_FN (decl))
+		{
+		  /* This function must have external linkage, as
+		     otherwise DECL_INTERFACE_KNOWN would have been
+		     set.  */
+		  gcc_assert (TREE_PUBLIC (decl));
+		  comdat_linkage (decl);
+		  DECL_INTERFACE_KNOWN (decl) = 1;
+		}
+	      else if (DECL_MAYBE_IN_CHARGE_CDTOR_P (decl))
+		/* For implicit instantiations of cdtors try to make
+		   it comdat, so that maybe_clone_body can use aliases.
+		   See PR113208.  */
+		maybe_make_one_only (decl);
 	    }
 	}
       else if (VAR_P (decl))
@@ -5264,7 +5271,19 @@ c_parse_final_cleanups (void)
 	    generate_tls_wrapper (decl);
 
 	  if (!DECL_SAVED_TREE (decl))
-	    continue;
+	    {
+	      cgraph_node *node;
+	      tree tgt;
+	      /* Even when maybe_clone_body created same body alias
+		 has no DECL_SAVED_TREE, if its alias target does,
+		 don't skip it.  */
+	      if (!DECL_CLONED_FUNCTION (decl)
+		  || !(node = cgraph_node::get (decl))
+		  || !node->cpp_implicit_alias
+		  || !(tgt = node->get_alias_target_tree ())
+		  || !DECL_SAVED_TREE (tgt))
+		continue;
+	    }
 
 	  cgraph_node *node = cgraph_node::get_create (decl);
 
@@ -5292,7 +5311,7 @@ c_parse_final_cleanups (void)
 		node = node->get_alias_target ();
 
 	      node->call_for_symbol_thunks_and_aliases (clear_decl_external,
-						      NULL, true);
+							NULL, true);
 	      /* If we mark !DECL_EXTERNAL one of the symbols in some comdat
 		 group, we need to mark all symbols in the same comdat group
 		 that way.  */
@@ -5302,7 +5321,7 @@ c_parse_final_cleanups (void)
 		     next != node;
 		     next = dyn_cast<cgraph_node *> (next->same_comdat_group))
 		  next->call_for_symbol_thunks_and_aliases (clear_decl_external,
-							  NULL, true);
+							    NULL, true);
 	    }
 
 	  /* If we're going to need to write this function out, and
--- gcc/cp/optimize.cc.jj	2024-04-25 09:47:24.936736833 +0200
+++ gcc/cp/optimize.cc	2024-04-25 10:19:25.338332564 +0200
@@ -220,10 +220,8 @@ can_alias_cdtor (tree fn)
   gcc_assert (DECL_MAYBE_IN_CHARGE_CDTOR_P (fn));
   /* Don't use aliases for weak/linkonce definitions unless we can put both
      symbols in the same COMDAT group.  */
-  return (DECL_INTERFACE_KNOWN (fn)
-	  && (SUPPORTS_ONE_ONLY || !DECL_WEAK (fn))
-	  && (!DECL_ONE_ONLY (fn)
-	      || (HAVE_COMDAT_GROUP && DECL_WEAK (fn))));
+  return (DECL_WEAK (fn) ? (HAVE_COMDAT_GROUP && DECL_ONE_ONLY (fn))
+			 : (DECL_INTERFACE_KNOWN (fn) && !DECL_ONE_ONLY (fn)));
 }
 
 /* FN is a [cd]tor, fns is a pointer to an array of length 3.  Fill fns
--- gcc/cp/decl.cc.jj	2024-04-24 18:28:22.231514532 +0200
+++ gcc/cp/decl.cc	2024-04-25 09:47:06.855991224 +0200
@@ -19254,6 +19254,14 @@ cxx_comdat_group (tree decl)
 	  else
 	    break;
 	}
+      /* If a ctor/dtor has already set the comdat group by
+	 maybe_clone_body, don't override it.  */
+      if (SUPPORTS_ONE_ONLY
+	  && TREE_CODE (decl) == FUNCTION_DECL
+	  && DECL_CLONED_FUNCTION_P (decl)
+	  && SUPPORTS_ONE_ONLY)
+	if (tree comdat = DECL_COMDAT_GROUP (decl))
+	  return comdat;
     }
 
   return decl;
--- gcc/testsuite/g++.dg/abi/comdat2.C.jj	2024-04-25 09:47:06.855991224 +0200
+++ gcc/testsuite/g++.dg/abi/comdat2.C	2024-04-25 09:47:06.855991224 +0200
@@ -0,0 +1,26 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2 -fkeep-inline-functions" }
+// { dg-final { scan-assembler "_ZN1BI1CEC5ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC1ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC2ERKS1_,comdat" } }
+
+template <typename T>
+struct A {
+  int foo () const;
+  A (int, int);
+};
+template <typename T>
+struct B : A<T> {
+  constexpr B (const B &x) : A<T> (1, x.foo ()) {}
+  B () : A<T> (1, 2) {}
+};
+struct C;
+struct D : B<C> {};
+void bar (D);
+
+void
+baz (D x)
+{
+  bar (x);
+}
--- gcc/testsuite/g++.dg/abi/comdat3.C.jj	2024-04-25 09:47:06.855991224 +0200
+++ gcc/testsuite/g++.dg/abi/comdat3.C	2024-04-25 09:47:06.855991224 +0200
@@ -0,0 +1,22 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2" }
+// { dg-final { scan-assembler "_ZN1M1SINS_1P1TELN1N1LE2EEC5Ev,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1M1SINS_1P1TELN1N1LE2EEC1Ev,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1M1SINS_1P1TELN1N1LE2EEC2Ev,comdat" } }
+
+namespace N { enum L { L1, L2, L3 } const O = L3; }
+namespace M {
+  using N::O;
+  using N::L;
+  template <typename, L = O>
+  struct S { constexpr S () {} };
+  namespace P {
+    struct T;
+    struct U { S<T> u; };
+    void foo () { U (); }
+  }
+  extern template class S<P::T>;
+}
+namespace p = M::P;
+template class M::S<p::T>;
--- gcc/testsuite/g++.dg/abi/comdat4.C.jj	2024-04-25 10:27:54.141172257 +0200
+++ gcc/testsuite/g++.dg/abi/comdat4.C	2024-04-25 10:28:22.493773334 +0200
@@ -0,0 +1,28 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2" }
+// { dg-final { scan-assembler "_ZN1BI1CEC5ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC1ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC2ERKS1_,comdat" } }
+
+template <typename T>
+struct A {
+  int foo () const;
+  A (int, int);
+};
+template <typename T>
+struct B : A<T> {
+  constexpr B (const B &x) : A<T> (1, x.foo ()) {}
+  B () : A<T> (1, 2) {}
+};
+struct C;
+struct D : B<C> {};
+void bar (D);
+
+void
+baz (D x)
+{
+  bar (x);
+}
+
+template struct B<C>;
--- gcc/testsuite/g++.dg/abi/comdat5.C.jj	2024-04-25 10:28:35.842585513 +0200
+++ gcc/testsuite/g++.dg/abi/comdat5.C	2024-04-25 10:28:52.413352362 +0200
@@ -0,0 +1,28 @@
+// PR lto/113208
+// { dg-do compile { target { c++11 && { *-*-*gnu* } } } }
+// { dg-additional-options "-O2" }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC5ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC1ERKS1_,comdat" } }
+// { dg-final { scan-assembler-not "_ZN1BI1CEC2ERKS1_,comdat" } }
+
+template <typename T>
+struct A {
+  int foo () const;
+  A (int, int);
+};
+template <typename T>
+struct B : A<T> {
+  constexpr B (const B &x) : A<T> (1, x.foo ()) {}
+  B () : A<T> (1, 2) {}
+};
+struct C;
+struct D : B<C> {};
+void bar (D);
+
+void
+baz (D x)
+{
+  bar (x);
+}
+
+extern template struct B<C>;
--- gcc/testsuite/g++.dg/lto/pr113208_0.C.jj	2024-04-25 09:47:06.856991210 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208_0.C	2024-04-25 09:47:06.855991224 +0200
@@ -0,0 +1,13 @@
+// { dg-lto-do link }
+// { dg-lto-options { {-O1 -std=c++20 -flto}} }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+// { dg-require-linker-plugin "" }
+
+#define CONSTEXPR constexpr
+#include "pr113208.h"
+
+struct QualityValue;
+struct k : vector<QualityValue> {};
+
+void m(k);
+void n(k i) { m(i); }
--- gcc/testsuite/g++.dg/lto/pr113208_1.C.jj	2024-04-25 09:47:06.856991210 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208_1.C	2024-04-25 09:47:06.856991210 +0200
@@ -0,0 +1,6 @@
+#define CONSTEXPR 
+#include "pr113208.h"
+
+struct QualityValue;
+vector<QualityValue> values1;
+vector<QualityValue> values{values1};
--- gcc/testsuite/g++.dg/lto/pr113208.h.jj	2024-04-25 09:47:06.856991210 +0200
+++ gcc/testsuite/g++.dg/lto/pr113208.h	2024-04-25 09:47:06.856991210 +0200
@@ -0,0 +1,10 @@
+template <typename _Tp> struct _Vector_base {
+  int g() const;
+  _Vector_base(int, int);
+};
+template <typename _Tp>
+struct vector : _Vector_base<_Tp> {
+  CONSTEXPR vector(const vector &__x)
+      : _Vector_base<_Tp>(1, __x.g()) {}
+ vector() : _Vector_base<_Tp>(1, 2) {}
+};


	Jakub