2 files changed, 32 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index a7dbc044b9f..8e31c070714 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1200,6 +1200,16 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
         MI.getOperand(0).setIsDebug();
 
         const DIExpression *DIExpr = MI.getDebugExpression();
+
+        // If we have a direct DBG_VALUE, and its location expression isn't
+        // currently complex, then adding an offset will morph it into a
+        // complex location that is interpreted as being a memory address.
+        // This changes a pointer-valued variable to dereference that pointer,
+        // which is incorrect. Fix by adding DW_OP_stack_value.
+        unsigned PrependFlags = DIExpression::ApplyOffset;
+        if (!MI.isIndirectDebugValue() && !DIExpr->isComplex())
+          PrependFlags |= DIExpression::StackValue;
+
         // If we have DBG_VALUE that is indirect and has a Implicit location
         // expression need to insert a deref before prepending a Memory
         // location expression. Also after doing this we change the DBG_VALUE
@@ -1211,8 +1221,7 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
           // Make the DBG_VALUE direct.
           MI.getOperand(1).ChangeToRegister(0, false);
         }
-        DIExpr =
-            DIExpression::prepend(DIExpr, DIExpression::ApplyOffset, Offset);
+        DIExpr = DIExpression::prepend(DIExpr, PrependFlags, Offset);
         MI.getOperand(3).setMetadata(DIExpr);
         continue;
       }
diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 1607cf5104f..900df27d1d3 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -926,6 +926,27 @@ bool DIExpression::isImplicit() const {
   return false;
 }
 
+bool DIExpression::isComplex() const {
+  if (!isValid())
+    return false;
+
+  if (getNumElements() == 0)
+    return false;
+
+  // If there are any elements other than fragment or tag_offset, then some
+  // kind of complex computation occurs.
+  for (const auto &It : expr_ops()) {
+    switch (It.getOp()) {
+      case dwarf::DW_OP_LLVM_tag_offset:
+      case dwarf::DW_OP_LLVM_fragment:
+        continue;
+      default: return true;
+    }
+  }
+
+  return false;
+}
+
 Optional<DIExpression::FragmentInfo>
 DIExpression::getFragmentInfo(expr_op_iterator Start, expr_op_iterator End) {
   for (auto I = Start; I != End; ++I)