[LLVMbugs] [Bug 660] NEW: [llvm-gcc] Add support for __attribute__((used))

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.cs.uiuc.edu/bugs/show_bug.cgi?id=660

           Summary: [llvm-gcc] Add support for __attribute__((used))
           Product: tools
           Version: trunk
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: normal
          Priority: P2
         Component: llvm-gcc
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org
                CC: markus at oberhumer.com


llvm-gcc should add support for attribute used.  It should do this in the following way:

1. If any globals/functions are marked with attribute((used)), the CFE should create a new appending 
global array "llvm.used", which has external linkage and is just an array of pointers to all of the globals 
that are 'used' (similar to the way that the %llvm.global_ctors list is emitted).
2. The internalize pass should not mark llvm.used internal under any circumstance.
3. The linker will already automatically concatenate these lists.

This will add new functionality (implementing a missing gcc feature), and it will also give Markus an 
elegant solution to the problem outlined in Bug 651.  Because the llvm.used array will have pointers to 
these, and because the array is external, the optimizer will never mess with these variables, even when 
using internalize.

-Chris



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