[llvm-bugs] [Bug 39413] New: GlobalMerge optimization drops visibility attributes

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39413

            Bug ID: 39413
           Summary: GlobalMerge optimization drops visibility attributes
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: rprichard at google.com
                CC: llvm-bugs at lists.llvm.org

The GlobalMerge optimization enabled with -Oz or -O3 appears to discard
visibility attributes from variables. The merged variables have default
visibility when they were declared as hidden or protected.

int somevar1 __attribute__((visibility("hidden"))) = 1;
int somevar2 __attribute__((visibility("hidden"))) = 2;
int somevar3 __attribute__((visibility("protected"))) = 1;
int somevar4 __attribute__((visibility("protected"))) = 2;
int get12() {
  return somevar1 + somevar2;
}
int get34() {
  return somevar3 + somevar4;
}

$ clang -target arm -Oz test.c -c && readelf -s test.o | grep somevar
    11: 00000000     4 OBJECT  GLOBAL DEFAULT    6 somevar1
    12: 00000004     4 OBJECT  GLOBAL DEFAULT    6 somevar2
    13: 00000008     4 OBJECT  GLOBAL DEFAULT    6 somevar3
    14: 0000000c     4 OBJECT  GLOBAL DEFAULT    6 somevar4

$ clang -target arm -Oz test.c -c -mno-global-merge && readelf -s test.o | grep
somevar
     9: 00000000     4 OBJECT  GLOBAL HIDDEN     6 somevar1
    10: 00000004     4 OBJECT  GLOBAL HIDDEN     6 somevar2
    11: 00000008     4 OBJECT  GLOBAL PROTECTED    6 somevar3
    12: 0000000c     4 OBJECT  GLOBAL PROTECTED    6 somevar4

This was originally reported against the Android NDK
(https://github.com/android-ndk/ndk/issues/829).

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