[llvm] r266893 - ModuleLinker: only import what is in GlobalsToImport, regarless if it is a function or not.

[Mehdi Amini via llvm-commits]

Conceptually, I see it as ThinLTO being slowly moving *away* from the ModuleLinker, bypassing most of the decision taken here.
And it makes sense: all the decisions should have already been taken earlier (using a real linker for instance). So the ModuleLinker part is getting thinner and thinner, till the point where we'll switch to talk to the IRMover directly!

-- 
Mehdi



> On Apr 20, 2016, at 11:32 AM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
> 
> nice!
> 
> On 20 April 2016 at 13:47, Mehdi Amini via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: mehdi_amini
>> Date: Wed Apr 20 12:47:42 2016
>> New Revision: 266893
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=266893&view=rev
>> Log:
>> ModuleLinker: only import what is in GlobalsToImport, regarless if it is a function or not.
>> 
>> The alias handling was specific to the old iterative inlining
>> mechanism, so that is dead now. The variable handling could make a
>> difference, since we were previously falling through to the normal
>> selection logic, but we don't observe changes in the validation
>> because no client seems to rely on it.
>> 
>> Differential Revision: http://reviews.llvm.org/D19307
>> 
>> From: Mehdi Amini <mehdi.amini at apple.com>
>> 
>> Modified:
>>    llvm/trunk/lib/Linker/LinkModules.cpp
>> 
>> Modified: llvm/trunk/lib/Linker/LinkModules.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Linker/LinkModules.cpp?rev=266893&r1=266892&r2=266893&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Linker/LinkModules.cpp (original)
>> +++ llvm/trunk/lib/Linker/LinkModules.cpp Wed Apr 20 12:47:42 2016
>> @@ -268,31 +268,15 @@ bool ModuleLinker::shouldLinkFromSource(
>>     return false;
>>   }
>> 
>> -  bool SrcIsDeclaration = Src.isDeclarationForLinker();
>> -  bool DestIsDeclaration = Dest.isDeclarationForLinker();
>> -
>>   if (isPerformingImport()) {
>> -    if (isa<Function>(&Src)) {
>> -      // For functions, LinkFromSrc iff this is a function requested
>> -      // for importing. For variables, decide below normally.
>> -      LinkFromSrc = GlobalsToImport->count(&Src);
>> -      return false;
>> -    }
>> -
>> -    // Check if this is an alias with an already existing definition
>> -    // in Dest, which must have come from a prior importing pass from
>> -    // the same Src module. Unlike imported function and variable
>> -    // definitions, which are imported as available_externally and are
>> -    // not definitions for the linker, that is not a valid linkage for
>> -    // imported aliases which must be definitions. Simply use the existing
>> -    // Dest copy.
>> -    if (isa<GlobalAlias>(&Src) && !DestIsDeclaration) {
>> -      assert(isa<GlobalAlias>(&Dest));
>> -      LinkFromSrc = false;
>> -      return false;
>> -    }
>> +    // LinkFromSrc iff this is a global requested for importing.
>> +    LinkFromSrc = GlobalsToImport->count(&Src);
>> +    return false;
>>   }
>> 
>> +  bool SrcIsDeclaration = Src.isDeclarationForLinker();
>> +  bool DestIsDeclaration = Dest.isDeclarationForLinker();
>> +
>>   if (SrcIsDeclaration) {
>>     // If Src is external or if both Src & Dest are external..  Just link the
>>     // external globals, we aren't adding anything.
>> 
>> 
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