[cfe-users] objc object file generated for gnustep runtime for ELF target is too big

[Perevalov Alexey via cfe-users]

I checked with lto, unfortunately, it didn't get rid of multiple .objc_protocol inclusions.

________________________________
От: llvm-dev <llvm-dev-bounces at lists.llvm.org> от имени Perevalov Alexey via llvm-dev <llvm-dev at lists.llvm.org>
Отправлено: 26 сентября 2016 г. 16:33
Кому: cfe-users at lists.llvm.org; llvm-dev at lists.llvm.org
Тема: [llvm-dev] objc object file generated for gnustep runtime for ELF target is too big

Dear community,


I'm using gnustep runtime -fobjc-runtime=gnustep with       gnustep-libobjc2 (https://github.com/gnustep/libobjc2) and
GitHub - gnustep/libobjc2<https://github.com/gnustep/libobjc2>
github.com
README.md GNUstep Objective-C Runtime. The GNUstep Objective-C runtime is designed as a drop-in replacement for the GCC runtime. It supports both a legacy and a ...



Cocotron/Chameleon.

For following source file

#import <Foundation/Foundation.h>
      #import <UIKit/UIKit.h>

int main(void)
        {
                NSString *str = [NSString stringWithCString:"TEST"];
                NSLog(@"test object %@", str);
                return 0;
        }

Compilation in xcode's clang
xcrun -sdk iphoneos clang -arch armv7s -mios-version-min=6.1 -c       test_foundation.m -o test_foundation_apple.o
gives following result:
1. object file has only 3156 bytes size
2. and in disassembler only main function
3. the final executable will be 49992 bytes size in this case


But compilation in llvm's clang downloaded from http://llvm.org/releases/3.8.0/clang+llvm-3.8.0-x86_64-apple-darwin.tar.xz

(
clang version 3.8.0 (tags/RELEASE_380/final)
      Target: x86_64-apple-darwin15.0.0
      Thread model: posix
      )
gives another results:
1. object file has 159044 bytes size
2. in disassembler a lot of unnecessary .objc_property_list,       .objc_method_list, .objc_protocol_list and .objc_protocol  in .bss       and .data section
3. the final binary size is 101837 bytes size



If comment in above sample #import <UIKit/UIKit.h, the size of       object file and binary file in xcode compilation will be the same,
but size binary and object file in case of       clang+llvm-3.8.0-x86_64-apple-darwin compilation will be reduced       sufficiently:
binary 28569 and object 36952 accordingly.



Looks like all protocols from UIKit.h is placed into       binary/object even it's not used there.
I got 3.9.0 from public git (branch release_39 of clang git       repository) and found that all protocols interpret as definition       (isThisDeclarationADefinition),
and in CGObjCGNU.cpp it's placed into object file whenever it's       used or not. With the same open source compiler and       -fobjc-runtime=ios protocols are not putting into
object file even in compilation for ELF (I used -target       arm-linux-gnueabi).
I used default binutil linker, not llvm's ld.ldd, due to I have problem with relocation on ARM.
I didn't use LTO, due to my linker doesn't have plugin support (I didnt' yet recompile it).

Could somebody point me where to solve that problem, is it AST       generation stage, or linkage stage or maybe it's not a problem and just LTO could be solution here?




p.s. It's not only one issue found by me in gnustep runtime       generation, and I'll report these issues in next emails.





         Best regards,
        Alexey Perevalov

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