[SafeStack] Insert the deref before remaining elements

This is a follow up to D64971. While we need to insert the deref after
the offset, it needs to come before the remaining elements in the
original expression since the deref needs to happen before the LLVM
fragment if present.

Differential Revision: https://reviews.llvm.org/D65172

llvm-svn: 366865

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index b6d555cd13e..8e501728599 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1599,13 +1599,8 @@ static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
 
   // Insert the offset before the first deref.
   // We could just change the offset argument of dbg.value, but it's unsigned...
-  if (Offset) {
-    SmallVector<uint64_t, 4> Ops;
-    DIExpression::appendOffset(Ops, Offset);
-    Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
-    Ops.push_back(dwarf::DW_OP_deref);
-    DIExpr = Builder.createExpression(Ops);
-  }
+  if (Offset)
+    DIExpr = DIExpression::prepend(DIExpr, 0, Offset);
 
   Builder.insertDbgValueIntrinsic(NewAddress, DIVar, DIExpr, Loc, DVI);
   DVI->eraseFromParent();