[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

17 files changed, 359 insertions, 71 deletions

diff --git a/debuginfo-tests/asan-deque.cpp b/debuginfo-tests/asan-deque.cpp
new file mode 100644
index 00000000000..19183d6cc15
--- /dev/null
+++ b/debuginfo-tests/asan-deque.cpp
@@ -0,0 +1,46 @@
+// RUN: %clangxx -arch x86_64 %target_itanium_abi_host_triple -O1 -g %s -o %t.out -fsanitize=address
+// RUN: %test_debuginfo %s %t.out
+// REQUIRES: not_asan
+//           Zorg configures the ASAN stage2 bots to not build the asan
+//           compiler-rt. Only run this test on non-asanified configurations.
+
+#include <deque>
+
+struct A {
+  int a;
+  A(int a) : a(a) {}
+};
+
+using log_t = std::deque<A>;
+
+static void __attribute__((noinline, optnone)) escape(log_t &log) {
+  static volatile log_t *sink;
+  sink = &log;
+}
+
+int main() {
+  log_t log;
+  log.emplace_back(1234);
+  log.emplace_back(56789);
+  escape(log);
+  // DEBUGGER: break 25
+  while (!log.empty()) {
+    auto record = log.front();
+    log.pop_front();
+    escape(log);
+    // DEBUGGER: break 30
+  }
+}
+
+// DEBUGGER: r
+
+// (at line 25)
+// DEBUGGER: p log
+// CHECK: 1234
+// CHECK: 56789
+
+// DEBUGGER: c
+
+// (at line 30)
+// DEBUGGER: p log
+// CHECK: 56789
diff --git a/llvm/include/llvm/CodeGen/SelectionDAG.h b/llvm/include/llvm/CodeGen/SelectionDAG.h
index a7b6db64a0a..888f9425ff9 100644
--- a/llvm/include/llvm/CodeGen/SelectionDAG.h
+++ b/llvm/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/llvm/include/llvm/IR/DebugInfoMetadata.h b/llvm/include/llvm/IR/DebugInfoMetadata.h
index 1743abc5398..82074685110 100644
--- a/llvm/include/llvm/IR/DebugInfoMetadata.h
+++ b/llvm/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
diff --git a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index 65ee3816f84..d6171f3177d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -697,11 +697,15 @@ InstrEmitter::EmitDbgValue(SDDbgValue *SD,
   if (SD->getKind() == SDDbgValue::FRAMEIX) {
     // Stack address; this needs to be lowered in target-dependent fashion.
     // EmitTargetCodeForFrameDebugValue is responsible for allocation.
-    return BuildMI(*MF, DL, TII->get(TargetOpcode::DBG_VALUE))
-        .addFrameIndex(SD->getFrameIx())
-        .addImm(0)
-        .addMetadata(Var)
-        .addMetadata(Expr);
+    auto FrameMI = BuildMI(*MF, DL, TII->get(TargetOpcode::DBG_VALUE))
+                       .addFrameIndex(SD->getFrameIx());
+    if (SD->isIndirect())
+      // Push [fi + 0] onto the DIExpression stack.
+      FrameMI.addImm(0);
+    else
+      // Push fi onto the DIExpression stack.
+      FrameMI.addReg(0);
+    return FrameMI.addMetadata(Var).addMetadata(Expr);
   }
   // Otherwise, we're going to create an instruction here.
   const MCInstrDesc &II = TII->get(TargetOpcode::DBG_VALUE);
diff --git a/llvm/lib/CodeGen/SelectionDAG/SDNodeDbgValue.h b/llvm/lib/CodeGen/SelectionDAG/SDNodeDbgValue.h
index 703eaa453ab..7e6b5742633 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SDNodeDbgValue.h
+++ b/llvm/lib/CodeGen/SelectionDAG/SDNodeDbgValue.h
@@ -71,20 +71,18 @@ public:
     u.Const = C;
   }
 
-  /// Constructor for frame indices.
-  SDDbgValue(DIVariable *Var, DIExpression *Expr, unsigned FI, DebugLoc dl,
-             unsigned O)
-      : Var(Var), Expr(Expr), DL(std::move(dl)), Order(O), IsIndirect(false) {
-    kind = FRAMEIX;
-    u.FrameIx = FI;
-  }
-
-  /// Constructor for virtual registers.
-  SDDbgValue(DIVariable *Var, DIExpression *Expr, unsigned VReg, bool indir,
-             DebugLoc dl, unsigned O)
-      : Var(Var), Expr(Expr), DL(std::move(dl)), Order(O), IsIndirect(indir) {
-    kind = VREG;
-    u.VReg = VReg;
+  /// Constructor for virtual registers and frame indices.
+  SDDbgValue(DIVariable *Var, DIExpression *Expr, unsigned VRegOrFrameIdx,
+             bool IsIndirect, DebugLoc DL, unsigned Order,
+             enum DbgValueKind Kind)
+      : Var(Var), Expr(Expr), DL(DL), Order(Order), IsIndirect(IsIndirect) {
+    assert((Kind == VREG || Kind == FRAMEIX) &&
+           "Invalid SDDbgValue constructor");
+    kind = Kind;
+    if (kind == VREG)
+      u.VReg = VRegOrFrameIdx;
+    else
+      u.FrameIx = VRegOrFrameIdx;
   }
 
   /// Returns the kind.
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 9870f21666f..1f2c50a69d9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -7391,11 +7391,13 @@ SDDbgValue *SelectionDAG::getConstantDbgValue(DIVariable *Var,
 /// FrameIndex
 SDDbgValue *SelectionDAG::getFrameIndexDbgValue(DIVariable *Var,
                                                 DIExpression *Expr, unsigned FI,
+                                                bool IsIndirect,
                                                 const DebugLoc &DL,
                                                 unsigned O) {
   assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
-  return new (DbgInfo->getAlloc()) SDDbgValue(Var, Expr, FI, DL, O);
+  return new (DbgInfo->getAlloc())
+      SDDbgValue(Var, Expr, FI, IsIndirect, DL, O, SDDbgValue::FRAMEIX);
 }
 
 /// VReg
@@ -7405,8 +7407,8 @@ SDDbgValue *SelectionDAG::getVRegDbgValue(DIVariable *Var,
                                           const DebugLoc &DL, unsigned O) {
   assert(cast<DILocalVariable>(Var)->isValidLocationForIntrinsic(DL) &&
          "Expected inlined-at fields to agree");
-  return new (DbgInfo->getAlloc()) SDDbgValue(Var, Expr, VReg, IsIndirect, DL,
-                                              O);
+  return new (DbgInfo->getAlloc())
+      SDDbgValue(Var, Expr, VReg, IsIndirect, DL, O, SDDbgValue::VREG);
 }
 
 void SelectionDAG::transferDbgValues(SDValue From, SDValue To,
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 12ce222075b..737bb1f9c9f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4973,13 +4973,20 @@ SDDbgValue *SelectionDAGBuilder::getDbgValue(SDValue N,
                                              unsigned DbgSDNodeOrder) {
   if (auto *FISDN = dyn_cast<FrameIndexSDNode>(N.getNode())) {
     // Construct a FrameIndexDbgValue for FrameIndexSDNodes so we can describe
-    // stack slot locations as such instead of as indirectly addressed
-    // locations.
-    return DAG.getFrameIndexDbgValue(Variable, Expr, FISDN->getIndex(), dl,
-                                     DbgSDNodeOrder);
+    // stack slot locations. 
+    //
+    // Consider "int x = 0; int *px = &x;". There are two kinds of interesting
+    // debug values here after optimization:
+    //
+    //   dbg.value(i32* %px, !"int *px", !DIExpression()), and
+    //   dbg.value(i32* %px, !"int x", !DIExpression(DW_OP_deref))
+    //
+    // Both describe the direct values of their associated variables.
+    return DAG.getFrameIndexDbgValue(Variable, Expr, FISDN->getIndex(),
+                                     /*IsIndirect*/ false, dl, DbgSDNodeOrder);
   }
-  return DAG.getDbgValue(Variable, Expr, N.getNode(), N.getResNo(), false, dl,
-                         DbgSDNodeOrder);
+  return DAG.getDbgValue(Variable, Expr, N.getNode(), N.getResNo(),
+                         /*IsIndirect*/ false, dl, DbgSDNodeOrder);
 }
 
 // VisualStudio defines setjmp as _setjmp
@@ -5191,9 +5198,9 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     // the MachineFunction variable table.
     if (FI != std::numeric_limits<int>::max()) {
       if (Intrinsic == Intrinsic::dbg_addr) {
-         SDDbgValue *SDV = DAG.getFrameIndexDbgValue(Variable, Expression,
-                                                     FI, dl, SDNodeOrder);
-         DAG.AddDbgValue(SDV, getRoot().getNode(), isParameter);
+        SDDbgValue *SDV = DAG.getFrameIndexDbgValue(
+            Variable, Expression, FI, /*IsIndirect*/ true, dl, SDNodeOrder);
+        DAG.AddDbgValue(SDV, getRoot().getNode(), isParameter);
       }
       return nullptr;
     }
@@ -5210,8 +5217,9 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
       auto FINode = dyn_cast<FrameIndexSDNode>(N.getNode());
       if (isParameter && FINode) {
         // Byval parameter. We have a frame index at this point.
-        SDV = DAG.getFrameIndexDbgValue(Variable, Expression,
-                                        FINode->getIndex(), dl, SDNodeOrder);
+        SDV =
+            DAG.getFrameIndexDbgValue(Variable, Expression, FINode->getIndex(),
+                                      /*IsIndirect*/ true, dl, SDNodeOrder);
       } else if (isa<Argument>(Address)) {
         // Address is an argument, so try to emit its dbg value using
         // virtual register info from the FuncInfo.ValueMap.
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(
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index a0e79b68e72..ae3cb077a3a 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1419,12 +1419,13 @@ bool llvm::LowerDbgDeclare(Function &F) {
       } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
         ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
       } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
-        // This is a call by-value or some other instruction that
-        // takes a pointer to the variable. Insert a *value*
-        // intrinsic that describes the alloca.
-        DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
-                                    DDI->getExpression(), DDI->getDebugLoc(),
-                                    CI);
+        // This is a call by-value or some other instruction that takes a
+        // pointer to the variable. Insert a *value* intrinsic that describes
+        // the variable by dereferencing the alloca.
+        auto *DerefExpr =
+            DIExpression::append(DDI->getExpression(), dwarf::DW_OP_deref);
+        DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(), DerefExpr,
+                                    DDI->getDebugLoc(), CI);
       }
     }
     DDI->eraseFromParent();
diff --git a/llvm/test/DebugInfo/AArch64/coalescing.ll b/llvm/test/DebugInfo/AArch64/coalescing.ll
index 0f65856fcb3..c39f8841948 100644
--- a/llvm/test/DebugInfo/AArch64/coalescing.ll
+++ b/llvm/test/DebugInfo/AArch64/coalescing.ll
@@ -20,10 +20,13 @@ entry:
   %0 = bitcast i32* %size to i8*, !dbg !15
   %call = call i8* @_Z3fooPv(i8* %0) #3, !dbg !15
   call void @llvm.dbg.value(metadata i32* %size, metadata !10, metadata !16), !dbg !17
+
+  ; The *location* of the variable should be $sp+12. This tells the debugger to
+  ; look up its value in [$sp+12].
   ; CHECK: .debug_info contents:
   ; CHECK: DW_TAG_variable
   ; CHECK-NEXT: DW_AT_location
-  ; CHECK-NEXT: DW_OP_breg31 WSP+12, DW_OP_deref
+  ; CHECK-NEXT: DW_OP_breg31 WSP+12
   ; CHECK-NEXT: DW_AT_name {{.*}}"size"
   ret void, !dbg !18
 }
diff --git a/llvm/test/DebugInfo/Mips/dsr-fixed-objects.ll b/llvm/test/DebugInfo/Mips/dsr-fixed-objects.ll
index 010186852ee..ebbe64a0c42 100644
--- a/llvm/test/DebugInfo/Mips/dsr-fixed-objects.ll
+++ b/llvm/test/DebugInfo/Mips/dsr-fixed-objects.ll
@@ -20,11 +20,12 @@ declare void @llvm.lifetime.end(i64, i8* nocapture)
 
 declare void @foo(i32*)
 
+; CHECK: DW_AT_name {{.*}}"f0"
 ; CHECK: DW_AT_name {{.*}}"e"
 ; CHECK: DW_TAG_variable
 ; CHECK-NEXT: DW_AT_location [DW_FORM_sec_offset] (
 ; CHECK-NEXT:   [0x00000028, 0x0000002c): DW_OP_reg1 AT_64
-; CHECK-NEXT:   [0x0000002c, 0x00000048): DW_OP_breg29 SP_64+16, DW_OP_deref)
+; CHECK-NEXT:   [0x0000002c, 0x00000048): DW_OP_breg29 SP_64+16)
 ; CHECK-NEXT: DW_AT_name [DW_FORM_strp]     ( .debug_str[0x0000006b] = "x")
 
 define i32 @f0(i32 signext %a, i32 signext %b, i32 signext %c, i32 signext %d, i32 signext %e) !dbg !4 {
@@ -55,7 +56,7 @@ entry:
 ; CHECK: DW_TAG_variable
 ; CHECK-NEXT: DW_AT_location [DW_FORM_sec_offset]  (
 ; CHECK-NEXT:   [0x00000080, 0x00000084): DW_OP_reg1 AT_64
-; CHECK-NEXT:   [0x00000084, 0x00000098): DW_OP_breg29 SP_64+16, DW_OP_deref)
+; CHECK-NEXT:   [0x00000084, 0x00000098): DW_OP_breg29 SP_64+16)
 ; CHECK-NEXT: DW_AT_name [DW_FORM_strp]     ( .debug_str[0x0000006b] = "x")
 
 define i32 @f1(i32 signext %a, i32 signext %b, i32 signext %c, i32 signext %d, i32 signext %e) !dbg !15 {
diff --git a/llvm/test/DebugInfo/X86/bbjoin.ll b/llvm/test/DebugInfo/X86/bbjoin.ll
index 02b6d416793..b3f20a9b8e3 100644
--- a/llvm/test/DebugInfo/X86/bbjoin.ll
+++ b/llvm/test/DebugInfo/X86/bbjoin.ll
@@ -12,7 +12,7 @@
 ; CHECK: ![[X:.*]] = !DILocalVariable(name: "x",
 ; CHECK: bb.0.entry:
 ; CHECK:   DBG_VALUE 23, debug-use $noreg, ![[X]],
-; CHECK:   DBG_VALUE debug-use $rsp, 0, ![[X]], !DIExpression(DW_OP_plus_uconst, 4, DW_OP_deref),
+; CHECK:   DBG_VALUE debug-use $rsp, debug-use $noreg, ![[X]], !DIExpression(DW_OP_plus_uconst, 4, DW_OP_deref),
 ; CHECK: bb.1.if.then:
 ; CHECK:   DBG_VALUE 43, debug-use $noreg, ![[X]],
 ; CHECK: bb.2.if.end:
diff --git a/llvm/test/DebugInfo/X86/dbg-value-const-byref.ll b/llvm/test/DebugInfo/X86/dbg-value-const-byref.ll
index 49d0ea2e82b..945c95f9913 100644
--- a/llvm/test/DebugInfo/X86/dbg-value-const-byref.ll
+++ b/llvm/test/DebugInfo/X86/dbg-value-const-byref.ll
@@ -25,7 +25,7 @@
 ; CHECK-NEXT:  [0x{{0*.*}}, 0x[[C1:.*]]): DW_OP_consts +3
 ; CHECK-NEXT:      [0x[[C1]], 0x[[C2:.*]]): DW_OP_consts +7
 ; CHECK-NEXT:      [0x[[C2]], 0x[[R1:.*]]): DW_OP_reg0 RAX
-; CHECK-NEXT:      [0x[[R1]], 0x[[R2:.*]]): DW_OP_breg7 RSP+4, DW_OP_deref)
+; CHECK-NEXT:      [0x[[R1]], 0x[[R2:.*]]): DW_OP_breg7 RSP+4)
 ; CHECK-NOT: DW_TAG
 ; CHECK: DW_AT_name{{.*}}"i"
 
diff --git a/llvm/test/DebugInfo/X86/dbg-value-frame-index.ll b/llvm/test/DebugInfo/X86/dbg-value-frame-index.ll
index b411f20a550..a2cf2cc4e29 100644
--- a/llvm/test/DebugInfo/X86/dbg-value-frame-index.ll
+++ b/llvm/test/DebugInfo/X86/dbg-value-frame-index.ll
@@ -20,10 +20,14 @@ while.end:
 }
 
 ; CHECK-LABEL: test
-; CHECK:       #DEBUG_VALUE: test:w <- [DW_OP_plus_uconst 8] [$rsp+0]
+; To get the value of the variable, we need to do [$rsp+8], i.e:
+; CHECK:       #DEBUG_VALUE: test:w <- [DW_OP_plus_uconst 8, DW_OP_deref] $rsp
 ; DWARF:  DW_AT_location [DW_FORM_sec_offset] (
 ; DWARF-NEXT:   [{{.*}}, {{.*}}): DW_OP_breg7 RSP+8)
 
+; Note: A previous version of this test checked for `[DW_OP_plus_uconst 8] [$rsp+0]`,
+; which is incorrect, because it adds the stack offset after dereferencing the stack pointer.
+
 declare i1 @fn(i64*, i64*, i64*, i8*, i64, i64*, i32*, i8*)
 declare void @llvm.dbg.value(metadata, metadata, metadata)
 
@@ -36,7 +40,7 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
 !3 = !{i32 2, !"Debug Info Version", i32 3}
 !4 = distinct !DISubprogram(name: "test", type: !10, unit: !0)
 !5 = !DILocalVariable(name: "w", scope: !4, type: !9)
-!6 = !DIExpression()
+!6 = !DIExpression(DW_OP_deref)
 !7 = !DILocation(line: 210, column: 12, scope: !4)
 !8 = !{!9}
 !9 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
diff --git a/llvm/test/DebugInfo/X86/debug-loc-frame.ll b/llvm/test/DebugInfo/X86/debug-loc-frame.ll
index 58b11857a45..f3bcfcb7377 100644
--- a/llvm/test/DebugInfo/X86/debug-loc-frame.ll
+++ b/llvm/test/DebugInfo/X86/debug-loc-frame.ll
@@ -28,7 +28,14 @@
 ; CHECK:      DW_TAG_variable
 ; CHECK:      DW_AT_location [DW_FORM_sec_offset] ({{.*}}
 ; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_reg0 RAX
-; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_breg7 RSP+4, DW_OP_deref)
+;
+; Note: This is a location, so we don't want an extra DW_OP_deref at the end.
+; LLDB gets the location right without it:
+;     Variable:  ... name = "val", type = "int", location =  [rsp+4], decl = frame.c:10
+; Adding the deref actually creates an invalid location:
+;     ... [rsp+4] DW_OP_deref
+;
+; CHECK-NEXT:   [{{0x.*}}, {{0x.*}}): DW_OP_breg7 RSP+4)
 ; CHECK-NEXT: DW_AT_name {{.*}}"val"
 
 ; ModuleID = 'frame.c'
diff --git a/llvm/test/Transforms/InstCombine/lower-dbg-declare.ll b/llvm/test/Transforms/InstCombine/lower-dbg-declare.ll
new file mode 100644
index 00000000000..44de3fc7531
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/lower-dbg-declare.ll
@@ -0,0 +1,183 @@
+; RUN: opt -instcombine < %s -S | FileCheck %s
+
+; This tests dbg.declare lowering for CallInst users of an alloca. The
+; resulting dbg.value expressions should add a deref to the declare's expression.
+
+; Hand-reduced from this example (-g -Og -fsanitize=address):
+
+;   static volatile int sink;
+;   struct OneElementVector {
+;     int Element;
+;     OneElementVector(int Element) : Element(Element) { sink = Element; }
+;     bool empty() const { return false; }
+;   };
+;   using container = OneElementVector;
+;   static void escape(container &c) { sink = c.Element; }
+;   int main() {
+;     container d1 = {42};
+;     while (!d1.empty())
+;       escape(d1);
+;     return 0;
+;   }
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.13.0"
+
+%struct.OneElementVector = type { i32 }
+
+define i1 @escape(%struct.OneElementVector* %d1) {
+  ret i1 false
+}
+
+; CHECK-LABEL: @main
+define i32 @main() !dbg !15 {
+entry:
+  %d1 = alloca %struct.OneElementVector, align 4
+  %0 = bitcast %struct.OneElementVector* %d1 to i8*, !dbg !34
+
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var:%.*]], metadata !DIExpression(DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  call void @llvm.dbg.declare(metadata %struct.OneElementVector* %d1, metadata !19, metadata !DIExpression()), !dbg !35
+  call i1 @escape(%struct.OneElementVector* %d1)
+  br label %while.cond, !dbg !37
+
+while.cond:                                       ; preds = %while.body, %entry
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var]], metadata !DIExpression(DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  %call = call i1 @escape(%struct.OneElementVector* %d1), !dbg !38
+  %lnot = xor i1 %call, true, !dbg !39
+  br i1 %lnot, label %while.body, label %while.end, !dbg !37
+
+while.body:                                       ; preds = %while.cond
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var]], metadata !DIExpression(DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  call i1 @escape(%struct.OneElementVector* %d1)
+  br label %while.cond, !dbg !37, !llvm.loop !42
+
+while.end:                                        ; preds = %while.cond
+  ret i32 0, !dbg !45
+}
+
+; CHECK-LABEL: @main2
+define i32 @main2() {
+entry:
+  %d1 = alloca %struct.OneElementVector, align 4
+  %0 = bitcast %struct.OneElementVector* %d1 to i8*, !dbg !34
+
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var:%.*]], metadata !DIExpression(DW_OP_lit0, DW_OP_mul, DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  call void @llvm.dbg.declare(metadata %struct.OneElementVector* %d1, metadata !19, metadata !DIExpression(DW_OP_lit0, DW_OP_mul)), !dbg !35
+  call i1 @escape(%struct.OneElementVector* %d1)
+  br label %while.cond, !dbg !37
+
+while.cond:                                       ; preds = %while.body, %entry
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var]], metadata !DIExpression(DW_OP_lit0, DW_OP_mul, DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  %call = call i1 @escape(%struct.OneElementVector* %d1), !dbg !38
+  %lnot = xor i1 %call, true, !dbg !39
+  br i1 %lnot, label %while.body, label %while.end, !dbg !37
+
+while.body:                                       ; preds = %while.cond
+; CHECK: dbg.value(metadata %struct.OneElementVector* [[var]], metadata !DIExpression(DW_OP_lit0, DW_OP_mul, DW_OP_deref))
+; CHECK-NEXT: call i1 @escape
+  call i1 @escape(%struct.OneElementVector* %d1)
+  br label %while.cond, !dbg !37, !llvm.loop !42
+
+while.end:                                        ; preds = %while.cond
+  ret i32 0, !dbg !45
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!2}
+!llvm.asan.globals = !{!8}
+!llvm.module.flags = !{!10, !11, !12, !13}
+!llvm.ident = !{!14}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "sink", linkageName: "_ZL4sink", scope: !2, file: !3, line: 1, type: !6, isLocal: true, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 7.0.0 (trunk 337207) (llvm/trunk 337204)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "test.cc", directory: "/Users/vsk/src/builds/llvm.org-master-RA")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !7)
+!7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!8 = !{}
+!9 = !{!"test.cc", i32 1, i32 21}
+!10 = !{i32 2, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{i32 1, !"wchar_size", i32 4}
+!13 = !{i32 7, !"PIC Level", i32 2}
+!14 = !{!"clang version 7.0.0 (trunk 337207) (llvm/trunk 337204)"}
+!15 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 18, type: !16, isLocal: false, isDefinition: true, scopeLine: 18, flags: DIFlagPrototyped, isOptimized: true, unit: !2, retainedNodes: !18)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!7}
+!18 = !{!19}
+!19 = !DILocalVariable(name: "d1", scope: !15, file: !3, line: 21, type: !20)
+!20 = !DIDerivedType(tag: DW_TAG_typedef, name: "container", file: !3, line: 12, baseType: !21)
+!21 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "OneElementVector", file: !3, line: 3, size: 32, flags: DIFlagTypePassByValue, elements: !22, identifier: "_ZTS16OneElementVector")
+!22 = !{!23, !24, !28}
+!23 = !DIDerivedType(tag: DW_TAG_member, name: "Element", scope: !21, file: !3, line: 4, baseType: !7, size: 32)
+!24 = !DISubprogram(name: "OneElementVector", scope: !21, file: !3, line: 6, type: !25, isLocal: false, isDefinition: false, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: true)
+!25 = !DISubroutineType(types: !26)
+!26 = !{null, !27, !7}
+!27 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !21, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!28 = !DISubprogram(name: "empty", linkageName: "_ZNK16OneElementVector5emptyEv", scope: !21, file: !3, line: 8, type: !29, isLocal: false, isDefinition: false, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true)
+!29 = !DISubroutineType(types: !30)
+!30 = !{!31, !32}
+!31 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!32 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !33, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!33 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !21)
+!34 = !DILocation(line: 21, column: 3, scope: !15)
+!35 = !DILocation(line: 21, column: 13, scope: !15)
+!36 = !DILocation(line: 21, column: 18, scope: !15)
+!37 = !DILocation(line: 22, column: 3, scope: !15)
+!38 = !DILocation(line: 22, column: 14, scope: !15)
+!39 = !DILocation(line: 22, column: 10, scope: !15)
+!40 = !DILocation(line: 23, column: 5, scope: !41)
+!41 = distinct !DILexicalBlock(scope: !15, file: !3, line: 22, column: 23)
+!42 = distinct !{!42, !37, !43}
+!43 = !DILocation(line: 24, column: 3, scope: !15)
+!44 = !DILocation(line: 26, column: 1, scope: !15)
+!45 = !DILocation(line: 25, column: 3, scope: !15)
+!46 = distinct !DISubprogram(name: "OneElementVector", linkageName: "_ZN16OneElementVectorC1Ei", scope: !21, file: !3, line: 6, type: !25, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !2, declaration: !24, retainedNodes: !47)
+!47 = !{!48, !50}
+!48 = !DILocalVariable(name: "this", arg: 1, scope: !46, type: !49, flags: DIFlagArtificial | DIFlagObjectPointer)
+!49 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !21, size: 64)
+!50 = !DILocalVariable(name: "Element", arg: 2, scope: !46, file: !3, line: 6, type: !7)
+!51 = !DILocation(line: 0, scope: !46)
+!52 = !DILocation(line: 6, column: 24, scope: !46)
+!53 = !DILocation(line: 6, column: 52, scope: !46)
+!54 = !DILocation(line: 6, column: 70, scope: !46)
+!55 = distinct !DISubprogram(name: "empty", linkageName: "_ZNK16OneElementVector5emptyEv", scope: !21, file: !3, line: 8, type: !29, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true, unit: !2, declaration: !28, retainedNodes: !56)
+!56 = !{!57}
+!57 = !DILocalVariable(name: "this", arg: 1, scope: !55, type: !58, flags: DIFlagArtificial | DIFlagObjectPointer)
+!58 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !33, size: 64)
+!59 = !DILocation(line: 0, scope: !55)
+!60 = !DILocation(line: 8, column: 24, scope: !55)
+!61 = distinct !DISubprogram(name: "escape", linkageName: "_ZL6escapeR16OneElementVector", scope: !3, file: !3, line: 14, type: !62, isLocal: true, isDefinition: true, scopeLine: 14, flags: DIFlagPrototyped, isOptimized: true, unit: !2, retainedNodes: !65)
+!62 = !DISubroutineType(types: !63)
+!63 = !{null, !64}
+!64 = !DIDerivedType(tag: DW_TAG_reference_type, baseType: !20, size: 64)
+!65 = !{!66}
+!66 = !DILocalVariable(name: "c", arg: 1, scope: !61, file: !3, line: 14, type: !64)
+!67 = !DILocation(line: 14, column: 31, scope: !61)
+!68 = !DILocation(line: 15, column: 12, scope: !61)
+!69 = !{!70, !71, i64 0}
+!70 = !{!"_ZTS16OneElementVector", !71, i64 0}
+!71 = !{!"int", !72, i64 0}
+!72 = !{!"omnipotent char", !73, i64 0}
+!73 = !{!"Simple C++ TBAA"}
+!74 = !DILocation(line: 15, column: 8, scope: !61)
+!75 = !{!71, !71, i64 0}
+!76 = !DILocation(line: 16, column: 1, scope: !61)
+!77 = distinct !DISubprogram(name: "OneElementVector", linkageName: "_ZN16OneElementVectorC2Ei", scope: !21, file: !3, line: 6, type: !25, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !2, declaration: !24, retainedNodes: !78)
+!78 = !{!79, !80}
+!79 = !DILocalVariable(name: "this", arg: 1, scope: !77, type: !49, flags: DIFlagArtificial | DIFlagObjectPointer)
+!80 = !DILocalVariable(name: "Element", arg: 2, scope: !77, file: !3, line: 6, type: !7)
+!81 = !DILocation(line: 0, scope: !77)
+!82 = !DILocation(line: 6, column: 24, scope: !77)
+!83 = !DILocation(line: 6, column: 35, scope: !77)
+!84 = !DILocation(line: 6, column: 59, scope: !85)
+!85 = distinct !DILexicalBlock(scope: !77, file: !3, line: 6, column: 52)
+!86 = !DILocation(line: 6, column: 70, scope: !77)
diff --git a/llvm/unittests/IR/MetadataTest.cpp b/llvm/unittests/IR/MetadataTest.cpp
index 12256bd2366..84a7b02fa98 100644
--- a/llvm/unittests/IR/MetadataTest.cpp
+++ b/llvm/unittests/IR/MetadataTest.cpp
@@ -2111,14 +2111,20 @@ TEST_F(DIExpressionTest, get) {
   // Test DIExpression::prepend().
   uint64_t Elts0[] = {dwarf::DW_OP_LLVM_fragment, 0, 32};
   auto *N0 = DIExpression::get(Context, Elts0);
-  N0 = DIExpression::prepend(N0, true, 64, true, true);
+  auto *N0WithPrependedOps = DIExpression::prepend(N0, true, 64, true, true);
   uint64_t Elts1[] = {dwarf::DW_OP_deref,
                       dwarf::DW_OP_plus_uconst, 64,
                       dwarf::DW_OP_deref,
                       dwarf::DW_OP_stack_value,
                       dwarf::DW_OP_LLVM_fragment, 0, 32};
   auto *N1 = DIExpression::get(Context, Elts1);
-  EXPECT_EQ(N0, N1);
+  EXPECT_EQ(N0WithPrependedOps, N1);
+
+  // Test DIExpression::append().
+  uint64_t Elts2[] = {dwarf::DW_OP_deref, dwarf::DW_OP_plus_uconst, 64,
+                      dwarf::DW_OP_deref, dwarf::DW_OP_stack_value};
+  auto *N2 = DIExpression::append(N0, Elts2);
+  EXPECT_EQ(N0WithPrependedOps, N2);
 }
 
 TEST_F(DIExpressionTest, isValid) {