[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338069 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 8 insertions, 2 deletions

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index a7b6db64a0a..888f9425ff9 100644
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -1250,8 +1250,8 @@ public:
 
   /// Creates a FrameIndex SDDbgValue node.
   SDDbgValue *getFrameIndexDbgValue(DIVariable *Var, DIExpression *Expr,
-                                    unsigned FI, const DebugLoc &DL,
-                                    unsigned O);
+                                    unsigned FI, bool IsIndirect,
+                                    const DebugLoc &DL, unsigned O);
 
   /// Creates a VReg SDDbgValue node.
   SDDbgValue *getVRegDbgValue(DIVariable *Var, DIExpression *Expr,
diff --git a/include/llvm/IR/DebugInfoMetadata.h b/include/llvm/IR/DebugInfoMetadata.h
index 1743abc5398..82074685110 100644
--- a/include/llvm/IR/DebugInfoMetadata.h
+++ b/include/llvm/IR/DebugInfoMetadata.h
@@ -2444,6 +2444,12 @@ public:
                                       SmallVectorImpl<uint64_t> &Ops,
                                       bool StackValue = false);
 
+  /// Append the opcodes \p Ops to \p DIExpr. Unlike \ref appendToStack, the
+  /// returned expression is a stack value only if \p DIExpr is a stack value.
+  /// If \p DIExpr describes a fragment, the returned expression will describe
+  /// the same fragment.
+  static DIExpression *append(const DIExpression *Expr, ArrayRef<uint64_t> Ops);
+
   /// Convert \p DIExpr into a stack value if it isn't one already by appending
   /// DW_OP_deref if needed, and appending \p Ops to the resulting expression.
   /// If \p DIExpr describes a fragment, the returned expression will describe