[deadargelim] Update dbg.value of 'unused' parameters

DeadArgElim pass marks unused function arguments as ‘undef’ without updating
existing dbg.values referring to it. As a consequence the debug info
metadata in the final executable was wrong.

Patch by Djordje Todorovic.

Differential Revision: https://reviews.llvm.org/D51968

llvm-svn: 342871

1 files changed, 8 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index cd2bd734eb2..0cf238b5d60 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -289,16 +289,21 @@ bool DeadArgumentEliminationPass::RemoveDeadArgumentsFromCallers(Function &Fn) {
     return false;
 
   SmallVector<unsigned, 8> UnusedArgs;
+  bool Changed = false;
+
   for (Argument &Arg : Fn.args()) {
-    if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() && !Arg.hasByValOrInAllocaAttr())
+    if (!Arg.hasSwiftErrorAttr() && Arg.use_empty() && !Arg.hasByValOrInAllocaAttr()) {
+      if (Arg.isUsedByMetadata()) {
+        Arg.replaceAllUsesWith(UndefValue::get(Arg.getType()));
+        Changed = true;
+      }
       UnusedArgs.push_back(Arg.getArgNo());
+    }
   }
 
   if (UnusedArgs.empty())
     return false;
 
-  bool Changed = false;
-
   for (Use &U : Fn.uses()) {
     CallSite CS(U.getUser());
     if (!CS || !CS.isCallee(&U))