[PATCH] c++, v4: Retry the aliasing of base/complete cdtor optimization at import_export_decl time [PR113208]

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Apr 24, 2024 at 08:43:46PM -0400, Jason Merrill wrote:
> > Then can_alias_cdtor would return false, because it ends with:
> >    /* 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))));
> > Should we change that DECL_INTERFACE_KNOWN (fn) in there to
> > (DECL_INTERFACE_KNOWN (fn) || something) then and what that
> > something should be?  HAVE_COMDAT_GROUP && DECL_ONE_ONLY (fn)?
> 
> Yes, I think reorganize to
> 
> ((DECL_INTERFACE_KNOWN (fn) && !DECL_WEAK (fn) && !DECL_ONE_ONLY (fn))
>  || (HAVE_COMDAT_GROUP && DECL_ONE_ONLY (fn))

I've tried the following patch, but unfortunately that lead to large
number of regressions:
+FAIL: g++.dg/coroutines/torture/co-yield-04-complex-local-state.C (test for excess errors)
+FAIL: g++.dg/coroutines/torture/func-params-08.C (test for excess errors)
+FAIL: g++.dg/coroutines/torture/func-params-09-awaitable-parms.C (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++11 (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++14 (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++17 (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++20 (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp0x/constexpr-initlist.C  -std=c++26 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++11 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++14 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++17 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++20 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp0x/initlist25.C  -std=c++26 (test for excess errors)
+FAIL: g++.dg/cpp1y/pr95226.C  -std=c++20 (test for excess errors)
+FAIL: g++.dg/cpp1y/pr95226.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp1y/pr95226.C  -std=c++26 (test for excess errors)
+FAIL: g++.dg/cpp1z/decomp12.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp1z/decomp12.C  -std=c++26 (test for excess errors)
+FAIL: g++.dg/cpp1z/eval-order2.C  -std=c++20 (test for excess errors)
+FAIL: g++.dg/cpp1z/eval-order2.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp1z/eval-order2.C  -std=c++26 (test for excess errors)
+FAIL: g++.dg/cpp2a/srcloc17.C  -std=c++20 (test for excess errors)
+FAIL: g++.dg/cpp2a/srcloc17.C  -std=c++23 (test for excess errors)
+FAIL: g++.dg/cpp2a/srcloc17.C  -std=c++26 (test for excess errors)
+FAIL: g++.old-deja/g++.jason/template31.C  -std=c++20 (test for excess errors)
+FAIL: g++.old-deja/g++.jason/template31.C  -std=c++23 (test for excess errors)
+FAIL: g++.old-deja/g++.jason/template31.C  -std=c++26 (test for excess errors)
+FAIL: 20_util/unique_ptr/creation/for_overwrite.cc  -std=gnu++26 (test for excess errors)
+FAIL: 23_containers/span/cons_1_assert_neg.cc  -std=gnu++20 (test for excess errors)
+FAIL: 23_containers/span/cons_1_assert_neg.cc  -std=gnu++26 (test for excess errors)
+FAIL: 23_containers/span/cons_2_assert_neg.cc  -std=gnu++20 (test for excess errors)
+FAIL: 23_containers/span/cons_2_assert_neg.cc  -std=gnu++26 (test for excess errors)
+FAIL: std/ranges/repeat/1.cc  -std=gnu++23 (test for excess errors)
+FAIL: std/ranges/repeat/1.cc  -std=gnu++26 (test for excess errors)

Errors are like:
func-params-08.C:(.text._ZNSt12_Vector_baseIiSaIiEEC2Ev[_ZNSt12_Vector_baseIiSaIiEEC5Ev]+0x14): undefined reference to `_ZNSt12_Vector_baseIiSaIiEE12_Vector_implC1EvQ26is_default_constructible_vIN9__gnu_cxx14__alloc_traitsIT0_NS5_10value_typeEE6rebindIT_E5otherEE'
Though, libstdc++.so.6 abilist is the same.
Trying to debug it now.

2024-04-24  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.
	* 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 10:04:18.049476567 +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))
--- 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