Un-revert r310014: false revert, it wasn't the cause of build break

llvm-svn: 310021

1 files changed, 25 insertions, 4 deletions

diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index 972b6a22324..f4702b377f9 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -668,10 +668,31 @@ DIExpression *DIBuilder::createExpression(ArrayRef<int64_t> Signed) {
   return createExpression(Addr);
 }
 
-DIExpression *DIBuilder::createFragmentExpression(unsigned OffsetInBytes,
-                                                  unsigned SizeInBytes) {
-  uint64_t Addr[] = {dwarf::DW_OP_LLVM_fragment, OffsetInBytes, SizeInBytes};
-  return DIExpression::get(VMContext, Addr);
+DIExpression *DIBuilder::createFragmentExpression(unsigned OffsetInBits,
+                                                  unsigned SizeInBits,
+                                                  const DIExpression *Expr) {
+  SmallVector<uint64_t, 8> Ops;
+  // Copy over the expression, but leave off any trailing DW_OP_LLVM_fragment.
+  if (Expr) {
+    for (auto Op : Expr->expr_ops()) {
+      if (Op.getOp() == dwarf::DW_OP_LLVM_fragment) {
+        // Make the new offset point into the existing fragment.
+        uint64_t FragmentOffsetInBits = Op.getArg(0);
+        uint64_t FragmentSizeInBits = Op.getArg(1);
+        assert((OffsetInBits + SizeInBits <= FragmentSizeInBits) &&
+               "new fragment outside of original fragment");
+        OffsetInBits += FragmentOffsetInBits;
+        break;
+      }
+      Ops.push_back(Op.getOp());
+      for (unsigned I = 0; I < Op.getNumArgs(); ++I)
+        Ops.push_back(Op.getArg(I));
+    }
+  }
+  Ops.push_back(dwarf::DW_OP_LLVM_fragment);
+  Ops.push_back(OffsetInBits);
+  Ops.push_back(SizeInBits);
+  return DIExpression::get(VMContext, Ops);
 }
 
 template <class... Ts>