[DebugInfo] LowerDbgDeclare: Add derefs when handling CallInst users

LowerDbgDeclare inserts a dbg.value before each use of an address
described by a dbg.declare. When inserting a dbg.value before a CallInst
use, however, it fails to append DW_OP_deref to the DIExpression.

The DW_OP_deref is needed to reflect the fact that a dbg.value describes
a source variable directly (as opposed to a dbg.declare, which relies on
pointer indirection).

This patch adds in the DW_OP_deref where needed. This results in the
correct values being shown during a debug session for a program compiled
with ASan and optimizations (see https://reviews.llvm.org/D49520). Note
that ConvertDebugDeclareToDebugValue is already correct -- no changes
there were needed.

One complication is that SelectionDAG is unable to distinguish between
direct and indirect frame-index (FRAMEIX) SDDbgValues. This patch also
fixes this long-standing issue in order to not regress integration tests
relying on the incorrect assumption that all frame-index SDDbgValues are
indirect. This is a necessary fix: the newly-added DW_OP_derefs cannot
be lowered properly otherwise. Basically the fix prevents a direct
SDDbgValue with DIExpression(DW_OP_deref) from being dereferenced twice
by a debugger. There were a handful of tests relying on this incorrect
"FRAMEIX => indirect" assumption which actually had incorrect
DW_AT_locations: these are all fixed up in this patch.

Testing:

- check-llvm, and an end-to-end test using lldb to debug an optimized
  program.
- Existing unit tests for DIExpression::appendToStack fully cover the
  new DIExpression::append utility.
- check-debuginfo (the debug info integration tests)

Differential Revision: https://reviews.llvm.org/D49454

llvm-svn: 338069

1 files changed, 39 insertions, 20 deletions

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index db28d9a242b..910e8c2fb74 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -841,9 +841,37 @@ DIExpression *DIExpression::prependOpcodes(const DIExpression *Expr,
   return DIExpression::get(Expr->getContext(), Ops);
 }
 
+DIExpression *DIExpression::append(const DIExpression *Expr,
+                                   ArrayRef<uint64_t> Ops) {
+  assert(Expr && !Ops.empty() && "Can't append ops to this expression");
+
+  // Copy Expr's current op list.
+  SmallVector<uint64_t, 16> NewOps;
+  for (auto Op : Expr->expr_ops()) {
+    // Append new opcodes before DW_OP_{stack_value, LLVM_fragment}.
+    if (Op.getOp() == dwarf::DW_OP_stack_value ||
+        Op.getOp() == dwarf::DW_OP_LLVM_fragment) {
+      NewOps.append(Ops.begin(), Ops.end());
+
+      // Ensure that the new opcodes are only appended once.
+      Ops = None;
+    }
+    Op.appendToVector(NewOps);
+  }
+
+  NewOps.append(Ops.begin(), Ops.end());
+  return DIExpression::get(Expr->getContext(), NewOps);
+}
+
 DIExpression *DIExpression::appendToStack(const DIExpression *Expr,
                                           ArrayRef<uint64_t> Ops) {
   assert(Expr && !Ops.empty() && "Can't append ops to this expression");
+  assert(none_of(Ops,
+                 [](uint64_t Op) {
+                   return Op == dwarf::DW_OP_stack_value ||
+                          Op == dwarf::DW_OP_LLVM_fragment;
+                 }) &&
+         "Can't append this op");
 
   // Append a DW_OP_deref after Expr's current op list if it's non-empty and
   // has no DW_OP_stack_value.
@@ -851,30 +879,21 @@ DIExpression *DIExpression::appendToStack(const DIExpression *Expr,
   // Match .* DW_OP_stack_value (DW_OP_LLVM_fragment A B)?.
   Optional<FragmentInfo> FI = Expr->getFragmentInfo();
   unsigned DropUntilStackValue = FI.hasValue() ? 3 : 0;
-  bool NeedsDeref =
-      (Expr->getNumElements() > DropUntilStackValue) &&
-      (Expr->getElements().drop_back(DropUntilStackValue).back() !=
-       dwarf::DW_OP_stack_value);
-
-  // Copy Expr's current op list, add a DW_OP_deref if needed, and ensure that
-  // a DW_OP_stack_value is present.
+  ArrayRef<uint64_t> ExprOpsBeforeFragment =
+      Expr->getElements().drop_back(DropUntilStackValue);
+  bool NeedsDeref = (Expr->getNumElements() > DropUntilStackValue) &&
+                    (ExprOpsBeforeFragment.back() != dwarf::DW_OP_stack_value);
+  bool NeedsStackValue = NeedsDeref || ExprOpsBeforeFragment.empty();
+
+  // Append a DW_OP_deref after Expr's current op list if needed, then append
+  // the new ops, and finally ensure that a single DW_OP_stack_value is present.
   SmallVector<uint64_t, 16> NewOps;
-  for (auto Op : Expr->expr_ops()) {
-    if (Op.getOp() == dwarf::DW_OP_stack_value ||
-        Op.getOp() == dwarf::DW_OP_LLVM_fragment)
-      break;
-    Op.appendToVector(NewOps);
-  }
   if (NeedsDeref)
     NewOps.push_back(dwarf::DW_OP_deref);
   NewOps.append(Ops.begin(), Ops.end());
-  NewOps.push_back(dwarf::DW_OP_stack_value);
-
-  // If Expr is a fragment, make the new expression a fragment as well.
-  if (FI)
-    NewOps.append(
-        {dwarf::DW_OP_LLVM_fragment, FI->OffsetInBits, FI->SizeInBits});
-  return DIExpression::get(Expr->getContext(), NewOps);
+  if (NeedsStackValue)
+    NewOps.push_back(dwarf::DW_OP_stack_value);
+  return DIExpression::append(Expr, NewOps);
 }
 
 Optional<DIExpression *> DIExpression::createFragmentExpression(