Fix a bug in Dead Argument Elimination.

  If a function seen at compile time is not necessarily the one linked to
the binary being built, it is illegal to change the actual arguments
passing to it. 

  e.g. 
   --------------------------
   void foo(int lol) {
     // foo() has linkage satisifying isWeakForLinker()
     // "lol" is not used at all.
   }

   void bar(int lo2) {
      // xform to foo(undef) is illegal, as compiler dose not know which
      // instance of foo() will be linked to the the binary being built.
      foo(lol2); 
   }
  -----------------------------

  Such functions can be captured by isWeakForLinker(). NOTE that
mayBeOverridden() is insufficient for this purpose as it dosen't include
linkage types like AvailableExternallyLinkage and LinkOnceODRLinkage.
Take link_odr* as an example, it indicates a set of *EQUIVALENT* globals
that can be merged at link-time. However, the semantic of 
*EQUIVALENT*-functions includes parameters. Changing parameters breaks
the assumption.

  Thank John McCall for help, especially for the explanation of subtle
difference between linkage types.

  rdar://11546243


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192302 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/Transforms/IPO/DeadArgumentElimination.cpp b/lib/Transforms/IPO/DeadArgumentElimination.cpp
index 6ee6162..8621f1a 100644
--- a/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -357,6 +357,19 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
   if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
     return false;
 
+  // If a function seen at compile time is not necessarily the one linked to
+  // the binary being built, it is illegal to change the actual arguments
+  // passing to it. These functions can be captured by isWeakForLinker().
+  // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
+  // dosen't include linkage types like AvailableExternallyLinkage and
+  // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
+  // *EQUIVALENT* globals that can be merged at link-time. However, the
+  // semantic of *EQUIVALENT*-functions includes parameters. Changing
+  // parameters breaks the assumption.
+  //
+  if (Fn.isWeakForLinker())
+    return false;
+
   if (Fn.use_empty())
     return false;