[llvm-bugs] [Bug 48501] New: Clang emits __attribute__((__used__)) functions in submodules that weren't imported

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48501

            Bug ID: 48501
           Summary: Clang emits __attribute__((__used__)) functions in
                    submodules that weren't imported
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Modules
          Assignee: unassignedclangbugs at nondot.org
          Reporter: teemperor at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

The example below reproduces the bug. 'use.h' is never actually imported by
main.cpp, but as it's in the same top-level module as 'other.h', the
'call_undefined' function is still deserialised and emitted. Note that this
happens with local-submodule-visibility turned on and off (at least with LSV=on
this seems like a bug):

$ cat main.cpp
#include "other.h"
int main() {}

$ cat other.h
struct Foo {
};

$ cat use.h
int undefined();
__attribute__((__used__))
inline int call_undefined() { undefined(); }

$ cat module.modulemap
module A {
  module Use { header "use.h" export * }
  module Other { header "other.h" export * }
}

$ clang main.cpp -fmodules -fcxx-modules  -Rmodule-build
-fmodules-cache-path=pcms -Xclang -fmodules-local-submodule-visibility
Undefined symbols for architecture x86_64:
  "undefined()", referenced from:
      call_undefined() in main-fe42f9.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

$ clang main.cpp -fmodules -fcxx-modules  -Rmodule-build
-fmodules-cache-path=pcms -Xclang -fmodules-local-submodule-visibility -S
-emit-llvm -o - | grep undefined
@llvm.used = appending global [1 x i8*] [i8* bitcast (i32 ()*
@_Z14call_undefinedv to i8*)], section "llvm.metadata"
define linkonce_odr i32 @_Z14call_undefinedv() #0 {
  %2 = call i32 @_Z9undefinedv()
declare i32 @_Z9undefinedv() #1

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