[PATCH] D24670: Fix unresolved linker symbols from misplaced extern definitions

[Chuck Atkins via llvm-commits]

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Chuck Atkins
Staff R&D Engineer, Scientific Computing
Kitware, Inc.
(518) 881-1183

On Wed, Sep 21, 2016 at 11:21 AM, Chuck Atkins <chuck.atkins at kitware.com>
wrote:

> chuckatkins updated this revision to Diff 72047.
> chuckatkins added a comment.
>
> Fix unresolved linker symbols from un-namespaced extern definitions
>
> When LCSSAID and LoopSimplifyID are declared extern inside a function body,
> some linkers will fail to resolve the actual symbols defined in the llvm
> namespace.  By removing the function local extern declarations and moving
> them to outside the function body, the symbols can be properly resolved.
> This is specifically an issue when building with the Intel compiler.
>
>
> https://reviews.llvm.org/D24670
>
> Files:
>   lib/Transforms/Utils/LoopUtils.cpp
>
> Index: lib/Transforms/Utils/LoopUtils.cpp
> ===================================================================
> --- lib/Transforms/Utils/LoopUtils.cpp
> +++ lib/Transforms/Utils/LoopUtils.cpp
> @@ -929,6 +929,14 @@
>    return UsedOutside;
>  }
>
> +// We locally access their IDs for LoopSimplify and LCSSA here because
> +// users shouldn't directly get them from this header.
> +namespace llvm
> +{
> +  extern char &LoopSimplifyID;
> +  extern char &LCSSAID;
> +}
> +
>  void llvm::getLoopAnalysisUsage(AnalysisUsage &AU) {
>    // By definition, all loop passes need the LoopInfo analysis and the
>    // Dominator tree it depends on. Because they all participate in the
> loop
> @@ -938,10 +946,7 @@
>    AU.addRequired<LoopInfoWrapperPass>();
>    AU.addPreserved<LoopInfoWrapperPass>();
>
> -  // We must also preserve LoopSimplify and LCSSA. We locally access
> their IDs
> -  // here because users shouldn't directly get them from this header.
> -  extern char &LoopSimplifyID;
> -  extern char &LCSSAID;
> +  // We must also preserve LoopSimplify and LCSSA.
>    AU.addRequiredID(LoopSimplifyID);
>    AU.addPreservedID(LoopSimplifyID);
>    AU.addRequiredID(LCSSAID);
>
>
>
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