GlobalMerge optimization drops ELF visibility attributes

[rprichard]

Bugzilla Link	39413
Resolution	FIXED
Resolved on	Feb 12, 2020 05:22
Version	trunk
OS	Linux
Blocks	#43900
CC	@davidbolvansky,@efriedma-quic,@zmodem,@pirama-arumuga-nainar,@mspang,@stephenhines,@yuanfang-chen

Extended Description

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 (android/ndk#829).

[rprichard]

assigned to @mspang

[mspang]

https://reviews.llvm.org/D73235

[zmodem]

https://reviews.llvm.org/D73235

That landed in

a2fb2c0

with a test fix follow-up in

6be9acd

Those were then merged to 10.x in
425198b
and 1f95a77

[zmodem]

mentioned in issue #43900