[PATCH] D30770: Ensure that prefix data is preserved with subsections-via-symbols

[Moritz Angermann via Phabricator via llvm-commits]

angerman reopened this revision.
angerman added a comment.
This revision is now accepted and ready to land.

So I've been playing with LLVM5 and GHC, and it seems like this solution is insufficient :-/ I've boiled this down to the following:

let `lib.ll`

  define void @f() prefix i32 123 {
   ret void
  }

and `dont-dead_strip-prefix-data.ll` be

  declare void @f();
  
  define i32 @main() {
   %f = bitcast void ()* @f to i32*
   %prefix_ptr = getelementptr inbounds i32, i32* %f, i32 -1
   %prefix_val = load i32, i32* %prefix_ptr
   %1 = icmp eq i32 %prefix_val, 123
   %2 = xor i1 %1, true
   %3 = zext i1 %2 to i32
   ret i32 %3
  }

This is almost identical to the example from before, only now we split this over two objects.

  clang -c lib.ll -o lib.o
  clang dont-dead_strip-prefix-data.ll lib.o -o dont-dead_strip-prefix-data -dead_stip && ./dont-dead_strip-prefix-data

Thus I believe we need a temporary global symbol instead.


Repository:
  rL LLVM

https://reviews.llvm.org/D30770