In C++ mode do not warn about inline combined with noinline [GH #183]

src/Changes

@@ -1,5 +1,26 @@
 Version 7.1
 
+10/21/26  [GH #183]
+GNU compatibility: "inline" combined with "noinline" on a definition
+
+In GNU and Clang C++ modes, the front end warned that a routine is both
+"inline" and "noinline" when a function definition was declared "inline" and
+had the GNU "noinline" attribute, but GCC accepts that combination silently
+(it is used, e.g., by Boost through "BOOST_NOINLINE inline").  For example:
+
+  inline __attribute__((noinline)) int f(int x) {  // No warning now.
+    return x;
+  }
+
+In C modes, where GCC and Clang warn about the combination in all of those
+cases, the behavior is unchanged.
+
+Also, instantiating a function template (or a member function of a class
+template) that is both "inline" and "noinline" no longer repeats the warning
+"At end of source" for each instance, only the template declarations are
+checked.
+
+
 10/21/26 [GH #335]
 Type transformations of qualified function types
 

src/attribute.c

@@ -6059,6 +6059,37 @@ that entity.
 
 #endif /* GNU_NAKED_ATTRIBUTE_ALLOWED || MICROSOFT_EXTENSIONS_ALLOWED */
 
+static a_boolean gnu_accepts_noinline_on_inline_routine(an_attribute_ptr  ap)
+/*
+ap is a GNU "noinline" attribute being applied to an inline routine.  Return
+TRUE if GCC accepts that combination silently in the context of ap. For
+example:
+
+  inline __attribute__((noinline)) int f() { return 0; }  // No warning.
+
+This idiom is used to ensure a noinline function in a header file does not
+cause linker errors.  GCC in C mode will warn on this while it does not in C++.
+*/
+{
+  a_boolean           result = FALSE;
+  a_decl_parse_state  *dps = (a_decl_parse_state*)ap->assoc_info;
+
+  if (!C_mode()) {
+    if (dps == NULL) {
+      /* The attribute is not being applied as part of a declaration, which
+         means it is being copied to a template instance. */
+      result = TRUE;
+    } else {
+      result = ap->on_primary_declaration &&
+               (dps->dso_flags &
+                     (DSO_INLINE | DSO_CONSTEXPR | DSO_CONSTEVAL)) != 0 &&
+               !dps->inline_on_earlier_decl;
+    }  /* if */
+  }  /* if */
+  return result;
+}  /* gnu_accepts_noinline_on_inline_routine */
+
+
 static char* apply_noinline_attr(an_attribute_ptr  ap,
                                  char              *entity,
                                  an_il_entry_kind  entity_kind)
@@ -6069,15 +6100,16 @@ and return the entity.
 {
   if (entity_kind == iek_routine) {
     a_routine_ptr  rp = (a_routine_ptr)entity;
+    a_boolean      has_always_inline = FALSE;
+#if GNU_EXTENSIONS_ALLOWED
+    has_always_inline = find_attribute(ak_always_inline,
+                                       rp->source_corresp.attributes) != NULL;
+#endif /* GNU_EXTENSIONS_ALLOWED */
     rp->never_inline = TRUE;
     if (rp->is_inline && is_gcc_attribute(ap) &&
         (!rp->source_corresp.is_class_member ||
-         rp->defined_outside_of_parent
-#if GNU_EXTENSIONS_ALLOWED
-         || find_attribute(ak_always_inline, rp->source_corresp.attributes)
-                                                                    != NULL
-#endif /* GNU_EXTENSIONS_ALLOWED */
-                                                                           )) {
+         rp->defined_outside_of_parent || has_always_inline) &&
+        (has_always_inline || !gnu_accepts_noinline_on_inline_routine(ap))) {
       pos_warning(ec_inline_gnu_noinline_conflict, &ap->position);
     }  /* if */
   } else {

src/decls.c

@@ -314,6 +314,7 @@ be restored).
   dps->has_direct_initializer = FALSE;
   dps->first_decl = FALSE;
   dps->first_decl_of_predeclared_entity = FALSE;
+  dps->inline_on_earlier_decl = FALSE;
   dps->override_okay = FALSE;
   dps->initializer_is_expr_list = FALSE;
   dps->no_special_cli_class_type_check = FALSE;
@@ -10374,6 +10375,9 @@ skip_overloading:;
       is_nothrow_type(rtp)) {
     routine_ptr->never_throws = TRUE;
   }  /* if */      
+  /* Record whether the routine was inline before this declaration (used when
+     applying the GNU "noinline" attribute). */
+  dps->inline_on_earlier_decl = routine_ptr->is_inline;
   if (func_info->is_inline) set_inline_flag(routine_ptr, TRUE);
   if (use_std_c99_inlining && !idlb.is_block_extern_decl) {
     /* In C99 mode the definition_for_inlining_only flag is set only if that is
@@ -11511,6 +11515,9 @@ definition of a member function of a class template.
         rout_ptr->is_constexpr = TRUE;
       }  /* if */
     }  /* if */
+    /* Record whether the routine was inline before this declaration (used when
+       applying the GNU "noinline" attribute). */
+    dps->inline_on_earlier_decl = rout_ptr->is_inline;
     if (!rout_ptr->is_inline) {
       if (func_info->is_inline || rout_ptr->is_declared_constexpr) {
         set_inline_flag(rout_ptr, TRUE);

src/decls.h

@@ -1061,6 +1061,11 @@ typedef struct a_decl_parse_state {
 			/* TRUE if this is the first declaration of a variable
 			   or function that was predeclared by the front
 			   end. */
+  a_bit_field	inline_on_earlier_decl:1;
+			/* TRUE if this declaration redeclares a function that
+			   was already inline before this declaration (e.g.,
+			   because an earlier declaration specified
+			   "inline"). */
   a_bit_field	redeclares_tag:1;
 			/* TRUE if the specifiers include a tag name (like
 			   "struct S" or "enum E") that must match a prior

src/func_def.c

@@ -2531,6 +2531,9 @@ member declaration (allowed in some Microsoft modes only).
        specification, and issue one if needed. */
     issue_no_exception_support_diag_on_throw_spec(func_info);
   }  /* if */
+  /* Record whether the routine was inline before this declaration (used when
+     applying the GNU "noinline" attribute). */
+  dps->inline_on_earlier_decl = rp->is_inline;
   if (func_info->is_inline) {
     if (!rp->is_inline) {
       set_inline_flag(rp, TRUE);

src/il.c

@@ -3284,12 +3284,15 @@ set).
 #endif /* MICROSOFT_EXTENSIONS_ALLOWED */
 #if GNU_EXTENSIONS_ALLOWED
   } else if (rp->never_inline && gnu_mode &&
+             (!rp->is_template_function || rp->is_specialized ||
+              rp->is_prototype_instantiation) &&
              (!rp->source_corresp.is_class_member ||
               rp->defined_outside_of_parent ||
               find_attribute(ak_always_inline, rp->source_corresp.attributes)
                                                                     != NULL)) {
     /* Was explicitly marked "noinline" previously and is now explicitly
-       marked inline. */
+       marked inline.  (An instance generated from a template is not
+       checked: the declarations of the template itself were.) */
     pos_warning(ec_inline_gnu_noinline_conflict, &error_position);
 #endif /* GNU_EXTENSIONS_ALLOWED */
   }  /* if */

tests/expectations/edg_x86_32_cp/regressions.log

@@ -1,3 +1,4 @@
+gh-183-redecl.sft.cpp:fp:-DTEST_NUMBER=1 --c++17:REQUIREMENTS NOT MET:
 gh-309.sft.cpp:fp:-DTEST_NUMBER=1 --g++:REQUIREMENTS NOT MET:
 gh-309.sft.cpp:fp:-DTEST_NUMBER=2 --g++ --no_exceptions:REQUIREMENTS NOT MET:
 immediate-pragma-lost.sft.cpp:cppbe:-DTEST_NUMBER=1:PASS:

tests/expectations/edg_x86_64_cp/regressions.log

@@ -1,3 +1,4 @@
+gh-183-redecl.sft.cpp:fp:-DTEST_NUMBER=1 --c++17:REQUIREMENTS NOT MET:
 gh-309.sft.cpp:fp:-DTEST_NUMBER=1 --g++:REQUIREMENTS NOT MET:
 gh-309.sft.cpp:fp:-DTEST_NUMBER=2 --g++ --no_exceptions:REQUIREMENTS NOT MET:
 immediate-pragma-lost.sft.cpp:cppbe:-DTEST_NUMBER=1:PASS:

tests/tests/imported/gnu/cpp/.Wattributes-3.rto/default.1.1.txt

@@ -3,10 +3,6 @@ fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_d
   ATTR ((__always_inline__))
   ^
 
-"Test_name.c", line 53: warning: routine is both "inline" and "noinline"
-  inline ATTR ((__noinline__))
-         ^
-
 "Test_name.c", line 58: warning: the "always_inline" attribute is ignored on non-inline functions
   ATTR ((__always_inline__))
   ^

tests/tests/imported/gnu/cpp/ext/.attr-noinline-2.rto/default.1.1.txt

@@ -3,7 +3,3 @@ fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_d
   fnoinline_always_inline<Special>()    // { dg-bogus "follows declaration" }
   ^
 
-"Test_name.c", line 58: warning: routine is both "inline" and "noinline"
-  fnoinline_always_inline<Special>()    // { dg-bogus "follows declaration" }
-  ^
-

tests/tests/imported/gnu/cpp/ext/.attr-noinline.rto/default.1.1.txt

@@ -3,7 +3,3 @@ fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_d
   fnoinline_always_inline<Special>()    // { dg-bogus "follows declaration" }
   ^
 
-"Test_name.c", line 112: warning: routine is both "inline" and "noinline"
-  fnoinline_always_inline<Special>()    // { dg-bogus "follows declaration" }
-  ^
-

tests/tests/imported/gnu/cpp/gcov/.gcov-10.rto/default.1.1.txt

@@ -1,5 +1 @@
 eccp -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"Test_name.c", line 9: warning: routine is both "inline" and "noinline"
-  inline int __attribute__ ((noinline)) Foo ()
-                             ^
-

tests/tests/imported/gnu/cpp/ipa/.nothrow-1.rto/default.1.1.txt

@@ -1,5 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"Test_name.c", line 11: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-

tests/tests/imported/gnu/cpp/ipa/.pure-const-1.rto/default.1.1.txt

@@ -1,5 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"Test_name.c", line 11: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-

tests/tests/imported/gnu/cpp/ipa/.pure-const-2.rto/default.1.1.txt

@@ -1,5 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"Test_name.c", line 10: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-

tests/tests/imported/gnu/cpp/ipa/.pure-const-3.rto/default.1.1.txt

@@ -1,9 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"./ipa/pure-const-3.h", line 7: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-
-"./ipa/pure-const-3.h", line 15: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-

tests/tests/imported/gnu/cpp/ipa/.pure-const-3b.rto/default.1.1.txt

@@ -1,9 +1 @@
 fe_only -DTEST_NUMBER=1 --gnu_version=999999 -tused -e 200 --no_wrap --no_wrap_diagnostics Test_name.c
-"./ipa/pure-const-3.h", line 7: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-
-"./ipa/pure-const-3.h", line 15: warning: routine is both "inline" and "noinline"
-  __attribute__ ((noinline))
-                  ^
-

tests/tests/regressions/.gh-183-negative.rto/default.1.1.txt

@@ -0,0 +1,58 @@
+fe_only -DTEST_NUMBER=1 --gnu_version=150000 --diag_error=inline_gnu_noinline_conflict --c++17 Test_name.c
+"Test_name.c", line 9: error: routine is both "inline" and "noinline"
+  inline NOINLINE int f1(int x);   // Error: not a definition.
+         ^
+
+"Test_name.c", line 10: error: routine is both "inline" and "noinline"
+  inline int f1(int x) { return x; }   // Error: inline after noinline.
+             ^
+
+"Test_name.c", line 12: error: routine is both "inline" and "noinline"
+  inline int f2(int x) NOINLINE;   // Error: not a definition.
+                       ^
+
+"Test_name.c", line 15: error: routine is both "inline" and "noinline"
+  inline int f3(int x) { return x; }   // Error: inline after noinline.
+             ^
+
+"Test_name.c", line 18: error: routine is both "inline" and "noinline"
+  inline NOINLINE int f4(int x) { return x; }   // Error: inline after
+                      ^
+
+"Test_name.c", line 22: error: routine is both "inline" and "noinline"
+  NOINLINE int f5(int x) { return x; }   // Error: noinline after inline.
+  ^
+
+"Test_name.c", line 25: error: routine is both "inline" and "noinline"
+  inline NOINLINE int f6(int x) { return x; }   // Error: noinline after
+         ^
+
+"Test_name.c", line 29: error: routine is both "inline" and "noinline"
+  constexpr NOINLINE int f7(int x) { return x; }   // Error: noinline after
+            ^
+
+"Test_name.c", line 38: error: routine is both "inline" and "noinline"
+  inline NOINLINE int A::m1(int x) { return x; }   // Error.
+         ^
+
+"Test_name.c", line 39: error: routine is both "inline" and "noinline"
+  inline NOINLINE int A::m2(int x) { return x; }   // Error (only once).
+                         ^
+
+"Test_name.c", line 40: error: routine is both "inline" and "noinline"
+  inline NOINLINE int A::m3(int x) { return x; }   // Error.
+         ^
+
+"Test_name.c", line 41: error: routine is both "inline" and "noinline"
+  template <class T> inline NOINLINE T A::m4(T x) { return x; }   // Error.
+                            ^
+
+"Test_name.c", line 47: error: routine is both "inline" and "noinline"
+  template <class T> inline T B<T>::m1(T x) { return x; }   // Error.
+                                    ^
+
+"Test_name.c", line 48: error: routine is both "inline" and "noinline"
+  template <class T> NOINLINE T B<T>::m2(T x) { return x; }   // Error.
+                     ^
+
+14 errors detected in the compilation of "Test_name.c".

tests/tests/regressions/.gh-183-redecl.rto/default.1.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 --gnu_version=150000 --diag_error=inline_gnu_noinline_conflict --c++17 Test_name.c

tests/tests/regressions/.gh-183.rto/default.1.1.txt

@@ -0,0 +1 @@
+fe_only -DTEST_NUMBER=1 --gnu_version=150000 --diag_error=inline_gnu_noinline_conflict --c++17 Test_name.c

tests/tests/regressions/gh-183-negative.sft.cpp

@@ -0,0 +1,55 @@
+//type:fn
+//options_all:--gnu_version=150000 --diag_error=inline_gnu_noinline_conflict
+//options:--c++17
+// Cases in which GCC still diagnoses "inline" combined with "noinline" in C++
+// (see gh-183.sft.cpp for the cases in which it does not): declarations that
+// are not definitions, and redeclarations that add one to the other.
+#define NOINLINE __attribute__((__noinline__))
+
+inline NOINLINE int f1(int x);   // Error: not a definition.
+inline int f1(int x) { return x; }   // Error: inline after noinline.
+
+inline int f2(int x) NOINLINE;   // Error: not a definition.
+
+NOINLINE int f3(int x);
+inline int f3(int x) { return x; }   // Error: inline after noinline.
+
+NOINLINE int f4(int x);
+inline NOINLINE int f4(int x) { return x; }   // Error: inline after
+                                              // noinline (only once).
+
+inline int f5(int x);
+NOINLINE int f5(int x) { return x; }   // Error: noinline after inline.
+
+inline int f6(int x);
+inline NOINLINE int f6(int x) { return x; }   // Error: noinline after
+                                              // inline.
+
+constexpr int f7(int x);
+constexpr NOINLINE int f7(int x) { return x; }   // Error: noinline after
+                                                 // inline.
+
+struct A {
+  inline NOINLINE int m1(int x);   // No error in the class.
+  NOINLINE int m2(int x);
+  inline int m3(int x);
+  template <class T> inline T m4(T x);
+};
+inline NOINLINE int A::m1(int x) { return x; }   // Error.
+inline NOINLINE int A::m2(int x) { return x; }   // Error (only once).
+inline NOINLINE int A::m3(int x) { return x; }   // Error.
+template <class T> inline NOINLINE T A::m4(T x) { return x; }   // Error.
+
+template <class T> struct B {
+  NOINLINE T m1(T x);
+  inline T m2(T x);
+};
+template <class T> inline T B<T>::m1(T x) { return x; }   // Error.
+template <class T> NOINLINE T B<T>::m2(T x) { return x; }   // Error.
+
+int g() {
+  A a;
+  B<int> b;   // Instantiating B<int>::m1 and m2 adds no further errors.
+  return f1(1) + f3(1) + f4(1) + f5(1) + f6(1) + f7(1) + a.m1(1) + a.m2(1) +
+         a.m3(1) + a.m4(1) + b.m1(1) + b.m2(1);
+}

tests/tests/regressions/gh-183-redecl.sft.cpp

@@ -0,0 +1,22 @@
+//type:fp
+//options_all:--gnu_version=150000 --diag_error=inline_gnu_noinline_conflict
+//options:--c++17
+//require:BACK_END_IS_CP_GEN_BE 0
+// Like gh-183.sft.cpp: GCC does not diagnose an "inline" definition with the
+// "noinline" attribute that follows a declaration without "inline".  (The
+// C++-generating back end puts out the earlier declaration with "inline", so
+// its generated code would legitimately be diagnosed; hence the requirement.)
+#define NOINLINE __attribute__((__noinline__))
+
+int f(int x);
+inline NOINLINE int f(int x) { return x; }
+
+struct A {
+  int m(int x);
+};
+inline NOINLINE int A::m(int x) { return x; }
+
+int g() {
+  A a;
+  return f(1) + a.m(1);
+}