From 1cab418ce228f33537322753c7befc51428a525f Mon Sep 17 00:00:00 2001
From: Shuxin Yang <shuxin.llvm@gmail.com>
Date: Wed, 9 Oct 2013 17:21:44 +0000
Subject: [PATCH] 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

llvm-svn: 192302
---
 llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp | 13 +++++++++++++
 llvm/test/Transforms/DeadArgElim/linkage.ll         | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 llvm/test/Transforms/DeadArgElim/linkage.ll

diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index 6ee6162..8621f1a 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/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;
 
diff --git a/llvm/test/Transforms/DeadArgElim/linkage.ll b/llvm/test/Transforms/DeadArgElim/linkage.ll
new file mode 100644
index 0000000..f475484
--- /dev/null
+++ b/llvm/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
+}
-- 
2.7.4