[llvm-bugs] [Bug 40300] New: lld-link does not detect duplicate symbols if optimizations are enabled

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40300

            Bug ID: 40300
           Summary: lld-link does not detect duplicate symbols if
                    optimizations are enabled
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: pavel.kryukov at phystech.edu
                CC: llvm-bugs at lists.llvm.org, peter.smith at linaro.org

Hi

Consider two following simple C sources defining 'int func()'

> PS D:\Dev> cat test.c
> int func() {
>     return 0;
> }
> PS D:\Dev> cat main.c
> int func() {
>     return 1;
> }
> 
> int main() {
>     return func();
> }

lld-link.exe does not warn about duplicate symbols

> PS D:\Dev> clang-cl /O1 /c test.c
> PS D:\Dev> clang-cl /O1 /c main.c
> PS D:\Dev> lld-link test.obj main.obj
> PS D:\Dev> .\test
> PS D:\Dev> lld-link.exe --version
> LLD 7.0.0

However, if we disable optimizations, warning appears:

> PS D:\Dev> clang-cl /c main.c
> PS D:\Dev> clang-cl /c test.c
> PS D:\Dev> lld-link test.obj main.obj
> lld-link.exe: error: duplicate symbol: func in test.obj and in main.obj

MSCV linker emits a warning in both cases (sorry for the Russian output)

> PS D:\Dev> clang-cl /O1 /c test.c
> PS D:\Dev> clang-cl /O1 /c main.c
> PS D:\Dev> link test.obj main.obj
> Microsoft (R) Incremental Linker Version 14.14.26430.0
> Copyright (C) Microsoft Corporation.  All rights reserved.
> 
> main.obj : error LNK2005: func уже определен в test.obj
> test.exe : fatal error LNK1169: обнаружен многократно определенный символ - один или более

GCC does the same:
> PS D:\Dev> gcc test.c -O1 -c
> PS D:\Dev> gcc main.c -O1 -c
> PS D:\Dev> gcc main.c -O1 -c
> PS D:\Dev> ld test.o main.o
> main.o:main.c:(.text+0x0): multiple definition of `func'
> test.o:test.c:(.text+0x0): first defined here
> main.o:main.c:(.text+0xd): undefined reference to `__main'

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