[DeadArgumentElimination] Preserve llvm.dbg.values's first argument

When removing return value Dead Argument Elimination pass clobbers first
llvm.dbg.value’s argument for live arguments of that function by replacing
it with nullptr. In the next pass it will be deleted, so debug location
about those arguments are lost. This change fixes it.

Patch by Djordje Todorovic.

Differential Revision: https://reviews.llvm.org/D42541

llvm-svn: 323784

1 files changed, 16 insertions, 8 deletions

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index a148ab65fc8..4f49312dfc4 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -329,12 +329,20 @@ bool ReplaceableMetadataImpl::isReplaceable(const Metadata &MD) {
   return dyn_cast<ValueAsMetadata>(&MD);
 }
 
-static Function *getLocalFunction(Value *V) {
+static DISubprogram *getLocalFunctionMetadata(Value *V) {
   assert(V && "Expected value");
-  if (auto *A = dyn_cast<Argument>(V))
-    return A->getParent();
-  if (BasicBlock *BB = cast<Instruction>(V)->getParent())
-    return BB->getParent();
+  if (auto *A = dyn_cast<Argument>(V)) {
+    if (auto *Fn = A->getParent())
+      return Fn->getSubprogram();
+    return nullptr;
+  }
+
+  if (BasicBlock *BB = cast<Instruction>(V)->getParent()) {
+    if (auto *Fn = BB->getParent())
+      return Fn->getSubprogram();
+    return nullptr;
+  }
+
   return nullptr;
 }
 
@@ -410,9 +418,9 @@ void ValueAsMetadata::handleRAUW(Value *From, Value *To) {
       delete MD;
       return;
     }
-    if (getLocalFunction(From) && getLocalFunction(To) &&
-        getLocalFunction(From) != getLocalFunction(To)) {
-      // Function changed.
+    if (getLocalFunctionMetadata(From) && getLocalFunctionMetadata(To) &&
+        getLocalFunctionMetadata(From) != getLocalFunctionMetadata(To)) {
+      // DISubprogram changed.
       MD->replaceAllUsesWith(nullptr);
       delete MD;
       return;