Fix members of an extern template class from being in every TU [GH #252]

Author: mborland

src/c_gen_be.c

@@ -10851,12 +10851,19 @@ if this routine has a body (dump nothing if it has no body).
   a_boolean       is_marked_weak = FALSE;
   a_boolean       thread_local_init_case = FALSE;
   a_boolean       for_inlining_only;
+  a_boolean       inline_only_defn = FALSE;
+  a_boolean       need_gnu_inline_attr = FALSE;
 
   if (c99_mode && rout->definition_for_inlining_only &&
-      !gcc_version_is(< 50000)) {
+      !gcc_version_is(< 50000)
+#if GNU_EXTENSIONS_ALLOWED
+      && !rout->gnu_c89_inline
+#endif /* GNU_EXTENSIONS_ALLOWED */
+                              ) {
     /* This is a C99 "inline definition", so we must suppress the "extern"
        keyword to avoid turning it into an external definition.  (gcc did
-       not support C99 inline semantics until version 5.1.0.) */
+       not support C99 inline semantics until version 5.1.0.  A routine with
+       the gnu_inline attribute follows the GNU C89 rules instead.) */
     for_inlining_only = TRUE;
   } else {
     for_inlining_only = FALSE;
@@ -10881,8 +10888,23 @@ if this routine has a body (dump nothing if it has no body).
          provided only for the purpose of inlining -- "extern inline".
          Put out the definition in that case. */
       has_defn = TRUE;
+      inline_only_defn = TRUE;
       if (!for_inlining_only) {
         storage_class = (a_storage_class)sc_extern;
+        /* "extern inline" is a definition only for inlining under the GNU
+           C89 rules, but an external definition under the C99 rules (the
+           gcc default since 5.1), so request the former with the gnu_inline
+           attribute. */
+        need_gnu_inline_attr = TRUE;
+#if GCC_IS_GENERATED_CODE_TARGET
+        if (gcc_is_generated_code_target &&
+            gnu_target_version_number < 40200) {
+          need_gnu_inline_attr = FALSE;
+        }  /* if */
+#endif /* GCC_IS_GENERATED_CODE_TARGET */
+#if GNU_EXTENSIONS_ALLOWED
+        if (rout->gnu_c89_inline) need_gnu_inline_attr = FALSE;
+#endif /* GNU_EXTENSIONS_ALLOWED */
       }  /* if */
     }  /* if */
   }  /* if */
@@ -11143,15 +11165,18 @@ if this routine has a body (dump nothing if it has no body).
 #endif /* MICROSOFT_EXTENSIONS_ALLOWED */
     if (gcc_or_clang_is_generated_code_target && rout->is_inline) {
       /* gcc will be used to compile this generated code, so we know how to
-         indicate an inline function. */
-      /* gcc ignores __inline__ on functions with ellipses, so don't
-         mark such functions as inline.  Recent versions of gcc issue an
-         error for a function marked both inline and weak, so don't mark a
-         weak function as inline, either. */
-      if (!f_skip_typerefs(rout->type)->variant.routine.extra_info->
-                                                                has_ellipsis &&
+         indicate an inline function. gcc ignores __inline__ on functions
+         with ellipses, so don't mark such functions as inline. Also,
+         recent versions of gcc issue an error for a function marked both
+         inline and weak, so don't mark a weak function as inline either */
+      if ((!f_skip_typerefs(rout->type)->variant.routine.extra_info->
+                                                               has_ellipsis ||
+           inline_only_defn) &&
           !is_marked_weak) {
         write_tok_str("__inline__ ");
+        if (need_gnu_inline_attr) {
+          write_tok_str("__attribute__((__gnu_inline__)) ");
+        }  /* if */
       }  /* if */
     }  /* if */
 #if GNU_EXTENSIONS_ALLOWED && !LOWER_IFUNC

src/pending_changes/gh-252-extern-inline-definitions.txt

@@ -0,0 +1,34 @@
+[GH #252]
+C-generating back end: inline-only definitions emitted as external ones
+
+When an inline function definition was to be used only for inlining (for
+example, a member of a class template specialization that is the subject of
+an explicit instantiation declaration), the C-generating back end emitted it
+as an "extern __inline__" definition for GCC and Clang.  That form is a
+definition only for inlining under the GNU C89 rules, but an external
+definition under the C99 rules that GCC uses by default since version 5.
+Every object file that used such a function then contained an external
+definition of it, and linking two such object files failed.  For example,
+with --c++17:
+
+  // a.h
+  template <class T> struct A {
+    int f() { return 1; }
+  };
+  extern template struct A<int>;
+
+  // a.cpp
+  #include "a.h"
+  int g1() { return A<int>().f(); }
+
+  // b.cpp
+  #include "a.h"
+  int g2() { return A<int>().f(); }  // Linking with a.cpp previously failed.
+
+The same problem affected GNU C89 "extern inline" functions, functions with
+the gnu_inline attribute in C99 and later C modes (which lost the "extern"
+keyword), and such definitions of functions with an ellipsis (which were not
+marked inline).  This is now fixed: The C-generating back end now adds the
+__gnu_inline__ attribute to "extern __inline__" definitions, keeps "extern"
+for functions with the gnu_inline attribute, and marks a definition only for
+inlining as inline even when the function has an ellipsis.

tests/expectations/edg_x86_64/imported.log

@@ -4211,7 +4211,6 @@ gnu/c/torture/pr68661-1a.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
 gnu/c/torture/pr68661-1b.sft.c:s:-DTEST_NUMBER=1:SKIPPED:
 gnu/c/torture/pr69242.sft.c:fp:-DTEST_NUMBER=1 -w:FAIL:
 gnu/c/torture/pr69886.sft.c:s:-DTEST_NUMBER=1 -w:SKIPPED:
-gnu/c/torture/pr70123.sft.c:rp:-DTEST_NUMBER=1:BADC(COMPILE):
 gnu/c/torture/pr70457.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr70985.sft.c:fp:-DTEST_NUMBER=1:FAIL:
 gnu/c/torture/pr71594.sft.c:s:-DTEST_NUMBER=1:SKIPPED:

tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.1.txt

@@ -59,8 +59,3 @@ eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics
   __attribute__ ((noinline, noclone)) int
                             ^
 
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1

tests/tests/imported/gnu/c/torture/.pr70123.rto/default.1.2.txt

@@ -0,0 +1 @@
+./a.out

tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_32_cp.1.1.txt

@@ -1,6 +1 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics --gcc Test_name.c
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1

tests/tests/imported/gnu/c/torture/.pr70123.rto/edg_x86_64_cp.1.1.txt

@@ -1,6 +1 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -e 200 --no_wrap --no_wrap_diagnostics --gcc Test_name.c
-eccp: diagnostics generated from compilation of Test_name.int.c:
-Test_name.c: In function 'baz':
-Test_name.c:15:8: error: invalid use of '__builtin_va_arg_pack ()'
-eccp: end of diagnostics from compilation of Test_name.int.c
-eccp: gcc compilation of Test_name.int.c returned an exit status of 1

tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/default.1.1.txt

@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:108: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:114: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:103:
 ./ext/va-arg-pack-1.C:127:108: error: invalid use of '__builtin_va_arg_pack ()'

tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32.1.1.txt

@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:93: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:99: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:88:
 ./ext/va-arg-pack-1.C:127:93: error: invalid use of '__builtin_va_arg_pack ()'

tests/tests/imported/gnu/cpp/ext/.va-arg-pack-1.rto/edg_x86_32_cp.1.1.txt

@@ -1,8 +1,5 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
 eccp: diagnostics generated from compilation of Test_name.int.c:
-./ext/va-arg-pack-1.C: In function '_Z3bariz':
-./ext/va-arg-pack-1.C:127:92: error: invalid use of '__builtin_va_arg_pack ()'
-./ext/va-arg-pack-1.C:128:98: error: invalid use of '__builtin_va_arg_pack ()'
 In function '_Z3bariz',
     inlined from 'main' at ./ext/va-arg-pack-1.C:134:88:
 ./ext/va-arg-pack-1.C:127:92: error: invalid use of '__builtin_va_arg_pack ()'