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, 21 insertions, 0 deletions

diff --git a/test/Transforms/DeadArgElim/linkage.ll b/test/Transforms/DeadArgElim/linkage.ll
new file mode 100644
index 0000000..f475484
--- /dev/null
+++ b/test/Transforms/DeadArgElim/linkage.ll
@@ -0,0 +1,21 @@
+; RUN: opt < %s -deadargelim -S | FileCheck %s
+
+; rdar://11546243
+%struct.A = type { i8 }
+
+define available_externally void @_Z17externallyDefinedP1A(%struct.A* %a) {
+entry:
+  call void @_Z3foov()
+  ret void
+}
+
+declare void @_Z3foov()
+
+define void @_Z4testP1A(%struct.A* %a) {
+; CHECK: @_Z4testP1A
+; CHECK: @_Z17externallyDefinedP1A(%struct.A* %a)
+
+entry:
+  call void @_Z17externallyDefinedP1A(%struct.A* %a)
+  ret void
+}