Change ModuleLinker to take a set of GlobalValues to import instead of a single one

For efficiency reason, when importing multiple functions for the same Module,
we can avoid reparsing it every time.

Differential Revision: http://reviews.llvm.org/D15102

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 254486
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 92764c9..8230d64 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -182,7 +182,10 @@
     }
 
     // Link in the specified function.
-    if (L.linkInModule(Module, Linker::Flags::None, &Index, F))
+    DenseSet<const GlobalValue *> FunctionsToImport;
+    FunctionsToImport.insert(F);
+    if (L.linkInModule(Module, Linker::Flags::None, &Index,
+                       &FunctionsToImport))
       report_fatal_error("Function Import: link error");
 
     // Process the newly imported function and add callees to the worklist.
@@ -194,6 +197,7 @@
 
     Changed = true;
   }
+
   return Changed;
 }